STUDY ON MICROSURGICAL RESECTION OF TUMORS OF THE INSULA

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SCTIMST HOSPITAL COMPLEX LIBRARY

PROJECT REPORT

SUBMITTED FOR M.Ch NEUROSURGERY

Dr. Kamal Prasad C.

November 2005

DEPARTMENTOFNEUROSURGERY

SREE CHITRA TIRUNAL INSTITUTE FOR

M (. H NJ ~ . MEDICAL SCIENCES AND TECHNOLOGY

THIRUVANANTHAPURAM - 695011

PROJECT REPORT

SUBMITTED FOR M.Ch NEUROSURGERY

Dr. Komal Prasad. C.

November 2005

DEPARTMENT OF NEUROSURGERY

SREE CHITRA TIRUNAL INSTITUTE FOR

MEDICAL SCIENCES AND TECHNOLOGY

THIRUVANANTHAPURAM - 695011

PROJECT REPORT

Title of the Project :

STUDY ON MICROSURGICAL RESECTION OF TUMORS OF THE INSULA

Name

Programme

Dr. Komal Prasad C.

M.Ch. Neurosurgery (3 years)

Month & Year of Submission : November 2005

ACKNOWLEDGEMENT

With a deep sense of gratitude and respect, I thank Prof. R.N. Bhattacharya,

Professor and Head, Department of Neurosurgery, for his constant inspiration,

able guidance and kind help in preparing this project and throughout my Neuro­

surgical training.

I am also deeply indebted to Prof. Suresh Nair, Professor of Neurosurgery,

for his valuable counsel during my Neurosurgical training and during the period of

this study.

I also wish to place on the record my immense gratitude to Dr. Ravi Mohan

Rao and Dr Girish Menon who have always been a constant source of

inspiration to me.

I am grateful to Dr Rajesh B.J. for his painstaking effort of going through the

work and giving this dissertation a final shape.

I am thankful to all other faculty members in my department namely Dr.

Mathew Abraham, Dr. Muthuretnam T and Dr Easwer H.V for all the support and

guidance.

I also like to mention my sincere thanks to all my colleagues who had helped

me to accomplish this project.

I am grateful to Dr. K. Mohand as, Director of the Institute, for giving permis­

sion to carry out this work and for all the institutional help required.

I also wish to thank all the staff of Neurosurgery and Medical records De­

partment for all the required help and support. Above all, I thank the Neurosurgi­

cal patients for making this study possible.

I fondly thank my wife, Dr. Shobha B., for her constant support during this

project and in my Neurosurgical venture. No words can describe the constant

motivation and moral support that my dear parents and sisters have always given

me.

(Dr. Komal Prasad C.)

INTRODUCTION

AIMS AND OBJECTIVES

PATIENTS AND METHODS

REVIEW OF LITERATURE

RESULTS

DISCUSSION

CONCLUSIONS

REFERENCES

CONTENTS

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INTRODUCTION

Surgical resection of tumors involving the insula represents a technical

challenge, because of its proximity to the internal capsule, the lenticulostriate

arteries and the lack of certainty concerning its functions. Because of its

complex anatomy, intrinsic tumours of the insular region were often

considered unresectable 1.

Majority of insular tumors are low grade in nature and are often

encountered in young patients. Insular lobe, along with supplementary motor

area, is preferentially involved by low-grade gliomas. This preferential

localization may be explained by developmental, cytomyeloarchitectonic,

neurochemical, metabolic, and functional reasons. The gliomas of the insula

and limbic system originate from the primitive layer of cortical zones, and

have the tendency to spread within the confines of these zones while sparing

the adjacent neocortical areas. Hence these tumors can be removed

aggressively with no or only minor neurological deficits.

Following developments in microneuroanatomy and microneurosurgical

techniques, radical surgical intervention in this area has become a challenging

option, with better results than other treatment modalities.

This study is a retrospective analysis reaffirming the feasibility of

microsurgical resection of insular tumors.

2

AIMS AND OBJECTIVES

1. To study the clinical features, imaging and histopathological

characteristics of insular tumors and their microsurgical implications.

2. To analyze the results and outcome of microsurgical resection of

insular tumors.

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PATIENTS AND METHODS

This is a retrospective analysis of patients with insular tumors admitted in

our institute between October 1998 and June 2005.

All patients with tumors involving predominantly the insula, as noted in

imaging studies and during surgery, were included in the study. Case records

of all the 69 patients with insular tumors admitted during the study period were

retrospectively analyzed.

Information from the records was recorded in a pro-forma. Follow up

details were collected from the hospital records. Patients not on regular follow

up were followed up by mail.

Data was analyzed using Microsoft Excel worksheet and SPSS 7.5

statistical program.

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REVIEW OF LITERATURE

Vicq d' Azyr was the first to declare an interest in the insula, which he

referred to as "the convolutions situated between the sylvian fissure and the

corpus striatum", in 1786. In 1809, Reil was the first to describe the insula,

which he named "die lnsel," and since that time the "insula" or "island of Reil"

has been the accepted nomenclature for this area2.

During the succeeding 50 years, the insula attracted little attention. In

approximately 1860, there was renewed interest on functions of insula and it

was thought to control the power of articulate speech, at least partly. Several

landmark articles were published at the end of 19th century, in which the

· anatomy of the insula and the surrounding regions were described in detail.

Recently, anatomical studies by Ture2, Varnavas3 and Rhoton4 further

elucidated the complex microsurgical anatomy of this region.

Insular phylogeny and architectonics

The insular lobe is a very complex anatomical, functional and physiological

system, which, as a part of mesocortex, connects the allocortex with the

neocortex. The cortical layers covering the basal nuclei in the early

embryonic stages form the insula until the end of the fifth month of gestation.

The apposition of the frontal, parietal and temporal opercula is completed only

at the end of gestation. This process transforms the insular cortex into a deep-

seated area that, nevertheless, represents superficial superolateral cortical

areas in gross anatomical form.

5

By cytoarchitectonic definition, the insula is part of the paralimbic system in

which the agranular allocortex is transformed into the granular isocortex. The

paralimbic system consists of three limbs- the orbitofrontal , temporopolar and

insular regions- which trifurcate at a central point, the pyriform olfactory

cortex. From this point the cytoarchitectonic cortical differentiation originates

in an analogous manner in all three paralimbic areas. The gradient of

increasingly more complex insular architecture is not oriented in a simple

anteroposterior direction but rather in a radial centrifugal fashion. Its

allocortical (limbic) center, the olfactory pyriform cortex is surrounded

concentrically by three mesocortical (paralimbic) layers- agranular,

dysgranular, and granular, which finally become identical to the granular

isocortex.

Thus, the structure of the insula is determined by a vector radiating from

an inner primitive core, connecting it with the limbic system toward higher

regions in its periphery, mainly the opercular cortex, which unites the

isocortex of the superolateral hemispheres (the neocortex)5•

Topographic anatomy of the insular region

The insula has a triangular shape with its apex directed anterior and

inferiorly towards the limen insulae, a slightly raised area overlying the

uncinate fasciculus covered by a thin layer of gray matter at the lateral border

of the anterior perforated substance. The limen is located at the junction of the

sphenoidal and operculo-insular compartments of the sylvian fissure.

The insula is encircled and separated from the frontal, parietal, and

6

temporal opercula by the shallow limiting sulcus. The limiting sulcus, although

roughly triangular in shape to conform to the shape of the insula, is commonly

referred to as the circular sulcus or the peri- insular sulcus, because it

encircles the insula.

The sulcus has three borders- superior, inferior and anterior; and three

angles- anteroinferior, anterosuperior and posterior where the borders join.

The anterior border is located deep to the pars triangularis of the inferior

frontal gyrus; the superior or upper border is nearly horizontal and separates

the upper border of the insula and the sylvian surface of the frontal and

parietal lobes; and the inferior or lower border is directed anteroinferiorly from

the posterior apex and separates the insula from the Sylvain surface of the

temporal lobe.

The anteroinferior angle is referred to as the insular apex by Rhoton4, but

Ture and Yasargil2 reserves the term 'insular apex' to the summit of the

pyramid shaped insula. The anterosuperior angle is located deep to the upper

anterior edge of the pars triangularis; and the posterior angle is located deep

to where the supramarginal gyrus wraps around the posterior end of the

sylvian fissure.

The anterosuperior angle is located lateral to the frontal horn and the

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posterior angle is located lateral to the atrium and corresponds to the sylvian

point, the site at which the most posterior branch of the insular segment of the

MCA turns laterally between the opercular lips to reach the cortical surface

and the anterioinferior angle points to the lateral edge of the anterior

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perforarted substance.

The insula covers the lateral surface of the central core of the hemispheric

core formed by the extreme, external and internal capsules, claustrum,

lentiform (putamen and globus pallidus) and caudate nuclei, and thalamus. It

is approximately coextensive with the claustrum and putamen.

The upper margin of the insula is located superficial to the midlevel of the

body and head of the caudate nucleus. The posterosuperior angle of the

insula, the site of the sylvian point, is situated superficial to the anterior margin

of the upper part of the atrium where the crus of the fornix wrap around the

pulvinar. The majority of the atrium is located behind the level of the

posterosuperior part or the circular sulcus. A surface landmark paralleling the

lower border of the insula is the superior temporal sulcus, and a deep

landmark paralleling the lower border is the optic tract coursing in the roof of

the ambient cistern near the midline.

The central insular sulcus, the main and deepest sulcus of the insula,

courses obliquely across the insula, in a similar direction to the central sulcus

of Rolando. It divides the insula into two zones that are unequal in size: the

anterior insula (larger) and posterior insula (smaller). In 90% of cases central

sulcus was well defined, extending from the superior peri-insular sulcus to the

limen insula in an uninterrupted line.

The larger anterior insula is composed of the transverse and accessory

insular gyri and three principal short insular gyri (anterior, middle and

posterior). The transverse and accessory insular gyri form the insular pole in

8

studies by Ture, which is the most anteroinferior aspect of the insula.

The anterosuperior border of the anterior short insular gyrus, at its junction

with the anterior and superior peri-insular sulci, is termed the 'anterior insular

point'. All gyri of the anterior insula appear to originate from the insular apex,

which is the portion nearest to the brain surface.

The posterior insula is composed of the anterior and posterior long gyri.

The posterior insular point is the term used to describe the confluence of the

superior and inferior peri-insular sulci, which continue along the deep portion

of the posterior ramus of the sylvian fissure as a common stem- 'postinsular

sulcus' 2.

The insula is closely related to the middle cerebral artery (MCA), from

which it receives its blood supply via 30-40 small arteries that spring from the

M2 and M3 segments. These arteries also supply the claustrum and the

extreme capsule but not the putamen, a pattern of vascular supply that is

determined during embryological development and indicates the common

origin of the insula and claustrum. Venous drainage is through the deep

middle cerebral vein which courses through the inferior limiting sulcus and

collects three other insular veins running in the central, precentral, and

superior limiting sulcus. The common insular venous trunk usually continues

-directly into the basal vein or rarely, drains superficially into the

sphenoparietal sinus.

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Surgical anatomv

Surgery on insular tumors requires a thorough anatomical knowledge of

insular region, including that of the sylvian cistern and middle cerebral artery

(MCA). The anatomical description is well elucidated in studies of Ture2,

Yasargi16 and Rhoton4.

Sylvian Cistern

The dissection of the sylvian cistern forms the most important initial step

for resection of insular tumors. Sylvian cistern consists of three distinct parts,

namely the fissure, opercular sulci and the fossa.

The Sylvian fissure is a long (10-14cm) division between fronto- orbital,

frontal parietal and temporal opercula. The proximal section (Sylvian stem,

horizontal- anterior- medial- sphenoidal limb) is located between the high

bifurcation of the ICA and the pars triangularis of the inferior frontal gyrus

(F3), where the basal fronto-orbital surface curves to the dorsal surface of the

frontal lobe (sylvian point). It is about 30 to 50mm long and has a C or S

shaped course.

The distal section of the sulcus (lateral or posterior limb) extends from the

sylvian point to the supramarginal gyrus. It measures 6 to em in length and

courses in a slightly undulating line due to the indentations of frontal, parietal

and temporal gyri into the sulcus.

The sylvian fissure is covered along its entire length with a superficial

arachnoid membrane, which may be very fine and transparent or extremely

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thick and opaque. The 5 to 6mm wide membrane covers the sylvian veins and

adhere scarcely to these veins.

Apart from the well described branches of the sylvian fissure as the

horizontal, ascending rami, diagonal, anterior and posterior subcentral,

posterior temporal sulci, Yasargil described several inter-opercular sulci

located between the opercular surfaces of the lateral orbital, inferior frontal,

inferior parietal and opercular surface of the superior temporal gyrus.

The sylvian fossa, hidden beneath the opercula, consists of three sections.

The proximal section is located between the bifurcation of the ICA and limen

insula, where the MCA bifurcates into superior and inferior trunks. It measures

30 to 39mm in length and 5 to 6mm in width and is named as vallecula or

preinsular sulcus. The M1 segment of MCA, the lateral lenticulostriate

arteries, deep sylvian vein and occasionally M2 segments course within the

proximal segment.

The middle (insular) section of the sylvian fossa is about 6 to 7cm long, 5

to 6cm wide and 3 to 5mm deep. It extends from level of limen insula to the

posterior insular point. The extension of the fossa underneath the opercula

creates four pouches. The anterior pouch extends beneath the lateral orbital

gyrus to the anerior peri-insular sulcus, the superior pouch extends beneath

· -the frontal operculum to the superior peri- insular sulcus, the posterior inferior

pouch extends beneath parietal operculum to the retroinsular fossa

(postinsular sulcus) and the inferior pouch extends beneath the temporal

operculum to the inferior peri-insular sulcus. Three to five short and two long

•.

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insular gyri are located at the base of the insular fossa. The external perimeter

of this group of gyri is delineated by peri-insular sulci.

The retro-insular fossa (or postinsular sulcus) is short but deep (4-Scm),

covered by the supramarginal gyrus, the transverse temporal gyri (Heschl)

and transverse parietal gyri and it contains arteries of the M3 segment which

course and curve around the parietal and temporal opercula to the surface.

All along these sections of the sylvian fossa, a dense network of pial­

arachnoid fibres intervene arteries, veins and pial surfaces of the adjacent

opercular and insular gyri.

Middle cerebral Artery (MCA)

1. Sphenoidal (M1J segment

The course of the M1 segment, which is 3-4cm long, does not always

·follows a straight diagonal line but it may take an undulating 'C' or'S' shaped

route. Furthermore in 10% of cases M1 segment may make a significant

curve posteriorly and can be obscured by the arch of limen insula. In 40% of

cases it makes a significant curve anteriorly. At surgical exploration, two,

three or even four arteries of equal size may be seen coursing parallel to each

other. This perplexing configuration can be resolved by further exploring these

arteries proximally as far as the internal carotid artery (ICA) bifurcation. It may

show early temporal bifurcation (10%) or early frontal bifurcation (8%).

Occasional (0.5%) accessory MCA that originates from a proximal or distal A1

segment may imitate a true duplication of M1 segment.

•.

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2. Insular (M2J segment

In 50% of cases, the M1 segment divides into superior and inferior M2

trunks, usually at the level of the limen insula. In 2% of cases, the M1

segment does not divide- it continues as a single trunk along the entire length

of the sylvian fossa and consistently branches to the frontal, parietal and

temporal areas.

In 15% of cases the superior M2 trunk and in a further 10% of cases the

inferior M2 trunk divide again in close proximity of the M1 bifurcation, which is

diagnosed as trifurcation in angiograms.

The superior M2 trunk does not give any branches to the temporal lobe; on

the contrary, the middle and inferior trunks give branches to both the temporal

and parietal areas.

The branches of the superior and inferior trunks course over the insular gyri

are along the insular sulci into the anterior and superior pouches of the sylvian

sulcus. At the level of the anterior and superior peri-insular gyri and within

retroinsular fossa, these branches angle 180 degrees and follow a return course

beneath the opercula as the opercular (M3) segment, pass through the narrow

sylvian fissure, and curve 180 degrees around the opercula, reaching the lateral

surface of frontal and parietal lobes as parasylvian (M4) segments. These

arteries, as terminal (MS) branches, continue over the gyral surfaces or are

hidden in the depth of sulci to the areas of middle frontal gyrus, pre and post

central gyri and superior parietal lobe, where they may connect to the AS

branches of the anerior cerebral artery.

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The inferior M2 trunk courses into the inferior pouch of the Sylvian fossa

beneath the temporal opercula, and gives anterior, middle, posterior and

temporo-occipital arteries, which pass the sylvian fissure beneath the

temporal operculum as M3 segments, reaching the surface of the temporal

lobe as M4 segments.

In 15% of cases, the inferior trunk gives branches to the pre and

postcentral and parietal areas. They course diagonally across the sylvian

fossa to reach the superior and posterior pouches of the sylvian fossa,

returning around the operculum to the lateral surface.

Arteries supplying the insula

The insula receives its blood supply predominantly from the M2 segment.

An examination of 40 hemispheres revealed 75 to 104 insular arteries

originating from this segment. Some insular arteries also arise from distal M1

and M3 segments, but M4 and M5 segments do not supply the insula. In each

hemisphere there were 96 insular arteries on an average, with diameter

ranging from 0.1 to 0.8mm. About 85-90% of insular arteries were short and

supplied the insular cortex and extreme capsule; 1 0% were medium sized and

also supplied the claustrum and external capsule; and the remaining 3 to 5%

were long and extended as far as the corona radiata. The long insular arteries

·· - - ···-·· · ·-are mostly located in the posterior region of the insula. Ture et al identified a

large caliber artery- the "insuloopercular artery" providing branches to both

insula and the medial surface of the operculum7.

The numerous small (average caliber, 0.03-0.1 mm) perforating arteries

(·.·

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that arise from M2 and M3 segments and their branches vascularise only the

insular cortex and subcortical layers of the white matter and reach few

millimeters deep, to the border of claustrum, but they do not penetrate deeper

into the lentiform nucleus and the internal capsule. Therefore, .these

perforators can be coagulated and severed, to devascularise the insular

lesions without causing ischemic infarctions in the subinsular structures.

However, the larger (diameter 0.2-0.Smm) perforators at the posterosuperior

corner of the insula should be intentionally preserved8•9•10.

Functions of the insula

Functional aspects of the insula have been studied in animals and

humans. Multiple afferent and efferent connections have been identified in

their relations to neocortical, limbic, thalamic, and various centers (basal

ganglia, internal capsule and hypothalamus), which explain the complex

functional spectrum of the insular lobe. These numerous behavioral affiliations

of the insula seem to follow a topographical gradient in an antero-ventral

dorsa-caudal direction.

The most relevant functional aspects include5-

1. The insula as a primary visceral/ autonomic sensory and motor area.

2. The insula as supplementary motor area.

3. Insular somato-sensory and auditory functions

4. Complex language functions

5. By connections with the limbic system, the insula as a balancing relay

between empirical experiences, affect and behaviour.

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Nomenclature of tumors involving the insular region:

The question may arise whether the term insular tumor is appropriate for

the lesions included in our series. Although only approximately half of the

tumors are insuloopercular tumors in the strict sense, the terminology is

justified for several reasons, as described by Zentner5. As already described,

the insular lobe is not a separate anatomical and functional entity but merely

the centerpiece of the para-limbic tripod (insular-frontoorbital-temporopolar).

Moreover, the insula cannot be separated from the limbic system and the

neocortex. It represents an essential functional relay between those systems

and is therefore anatomically closely related and interconnected with them.

Clear-cut structural borders between the insula and the neighboring systems

do not exist. Thus, the opercular neocortex, the paralimbic, and the limbic

areas form a complex that should be only regarded in its entirety. When tumor

growth occcurs within this system, it is always centered in the insula. It is

obvious in lesions confined to the insular lobe (mainly its middle and posterior

parts) which represents the "heart" of tumor expansion into the corresponding

neocortical opercula. Although not so readily obvious, tumor growth is always

centered in the anterior insula in those tumors encompassing the entire

paralimbic and/or limbic system as well. At the anterior insula limit, the

.. uncinate fasciculus connects the paralimbic areas with each other, and the

paralimbic and limbic systems join at the piriform olfactory cortex. Thus, tumor

growth in combined lesions will always propagate along these two crossroads

within the anterior insula.

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Clinical features:

There is no single clinical feature that can be attributed unequivocally to

the insular cortex alone because of its complex and incompletely understood

interconnections. Animal experiments coupled with observations in humans

provide the basis for topographical-functional correlations under stable,

reproducible conditions. The situation in the presence of a tumor is different,

because in all cases, surrounding structures or other parts of the paralimbic

and limbic system are involved in the pathology.

However, seizures with visceral sensations are a distinct feature of tumors

involving the insula. The ictal sequence occurs in full consciousness,

beginning with a sensation of laryngeal constriction and paresthesiae, often

unpleasant, affecting large cutaneous territories, most often at the onset of a

complex partial seizure. It is eventually followed by dysarthric speech and

focal motor convulsive symptoms. The insular origin of these symptoms was

supported by the data from functional cortical mapping of the insula by using

direct cortical stimulations 11 •12•

Language disorder in these patients appears characteristically different

from other forms of aphasias, as noted by Zentner5• There remains some

... ____ ... __ uncertainty as to whether language disorders that were observed in some

patients with left-side tumor are aphasic, anarthric, or apractic, and whether

they should be attributed to the insula, the opercula, or both. It appears to be

that aphemia-dysarthria of phonation without aphasia-is a purely

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frontoopercular syndrome and that partial or global aphasia constitutes an

insulo- or parietoopercular syndrome.

Surgery on the insular lobe

In contrast to the variety of cliniconeurological, physiological, and

anatomical studies that focus on the insula, there is a paucity of publications

in the surgical literature on this area. In the era before operating microscope,

surgery on the insular lobe carried enormous complications. Even after the

introduction of the operating microscope, the surgical literature has had only a

. few publications that primarily address the successful removal of extra-axial

lesions within or through the insular cortex13.

In addition to the oncological indication, surgery alleviates the primary

symptom of seizu(es in many of these patients, which cannot be achieved by

any alternate modalities of treatments, as radiotherapy. Though there are

some reports favoring interstitial radiotherapy14 or stereotactic biopsy followed

by radiotherapy15, with lesser complications, cytoreductive surgery forms the

modality of choice to treat these predominantly low-grade tumors.

Yasargil16 demonstrated the feasibility of using surgical treatment for intra­

axial insular lesions in a large series of limbic and paralimbic tumors. He

studied the clinical manifestations, findings management and outcome of a

series of 240 cases with tumors of the limbic and paralimbic systems. He

classified limbic and paralimbic areas into eight categories -

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(1) Mediobasal temporal (amygdala, hippocampus, parahippocampus)

(2) Insular area (with or without frontoopercular and temporoopercular

areas)

(3) Frontoorbital- anterior insula- amygdala and temporal pole

(4) Cingular area

(5) Septal area

(6) Corpus fornices,

(7) Mammillary body and

(8) Entire limbic and paralimbic areas.

In his analysis of 177 cases of tumors situated in first three areas, 97 were

mediobasal temporal, 57 were in insular area, and 23 were in frontoorbital­

anterior insula- amygdala and temporal pole area. There was no operative

mortality. In his study, postoperatively 95% had no or only minor neurological

deficits. Preoperatively 77% of the patients had seizures, but 84% became

seizure-free after tumor removal.

He noted that large tumors are often the easier to extract. He suggested

that, by gradual and slow displacement of normal structures, a "birthchannel"

is created through which the tumor is delivered. Small tumors are difficult to

extract, as there was minimal displacement of surrounding structures. This

series demonstrated the efficacy of highly skilled microneurosurgery.

19

Zentner et al. 5 reported a detailed analysis of thirty patients with insular

tumors including 5 purely insular cases, 9 insular-opercular cases and 16

insular- paralimbic cases. Overall 100% resection was achieved in 5 cases

(17%), more than 80% resection in 21 cases (70%), and less than 80% in 4

cases (13%), based on estimates from comparisons of preoperative and

postoperative MR images. There were no deaths but 19 patients (63%)

experienced a complicated postoperative course. Hemiparesis occurred in

four cases (13%), aphasia occurred in 3 (21%) of the 14 cases in which

tumors were located in the left hemisphere.

Zentner also pointed out that, whereas WHO Grade Ill tumors may be

clinicopathologically similar to the "distinct" group of limbic and paralimbic low­

grade gliomas, glioblastomas of the insula, unlike low- and intermediate-grade

tumors, do not have a pattern of behavior that differs essentially from that

displayed by glioblastomas in other locations. The indication for surgical

therapy of glioblastomas of insula is therefore exposed to the same pros and

cons as in other locations. Zentner et al. concluded that resection of insular

tumors was feasible but the risks of insular resection were not insignificant.

Duffau 17 and associates described their series of 12 resected insular

tumors. All patients had low-grade gliomas. Only one tumor (8%) was purely

--------------------insular and only two (17%) were located in the dominant hemisphere. Four

patients (33%) underwent complete resection, 6 patients (50%) underwent

subtotal resection and 2 patients (17%) underwent partial resection. There

were no operative deaths but seven patients (58%) displayed an immediate

I

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postoperative deficit. These authors emphasized the role of direct brain

stimulation to identify the internal capsule and avoid postoperative motor

deficits.

Lang et al. 18 studied a series of 22 patients in which most patients

presented with seizures, and 50% had low-grade tumors. 75% or greater

resection was achieved in 73% of patients. Immediate neurological

dysfunction, primarily dysphasia and/ or hemiparesis, occurred in 36% of

cases, but permanent neurological deficits occurred in 9%, despite the fact

that, tumors were large and 59% of cases were located in dominant

hemisphere.

Surgical technique

The approach to insular tumors is described by Yasargil19·20•21 and more

recently by Lang22 in their large studies.

Positioning and opening

The resection of an insular tumor is performed with the patient in supine

position and shoulder elevated on a roll. The patient's head is extended and

rotated 30 to 45 degrees to the opposite side. This position allows the frontal

and temporal opercula to fall open as the arachnoid is sharply dissected.

A standard frontotemporal craniotomy is performed with nibbling of the

sphenoid bone. Dura is opened based anteriorly on the sphenoid wing. The

extent of tumor and its relation to the sylvian fissure may be ascertained using

intraoperative ultrasound at this stage.

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Anatomical dissection and tumor removal

The technique for anatomic dissection of insular tumor can be separated

into five stages, as proposed by Lang22.

1. Sylvian fissure dissection

As the insula is completely covered by the frontal, parietal, and the

temporal opercula, long and wide splitting of the sylvian fissure from the limen

insula to the gyrus circumflexus, typically 6 to 7 em in length is critical.

Widening of the sylvian fissure follows the splitting, by dissection into the peri­

insular sulci. Large veins crossing the sylvian fissure, particularly those at the

distal part should be mobilized and preserved if at all possible. Small veins

may be sacrificed. The tumor often helps with dissection by widening the

sulcus or by causing the insular apex to split the sylvian fissure.

2. MCA exposure

As the sylvian fissure is split, the MCA vessels are exposed. In fact,

dissection of the M2 vessels aids in opening of the fissure.

The initial step is uncovering and identifying the M2 branches to prevent

inadvertent coagulation during tumor removal. Next, following M2 branches to

the peri- insular sulci exposes MCA and all its branches.

Then, the M2 branches are isolated so that the short perforators arising

from the deep side of M2 branches can be identified and cut.

M 1 segment is followed to identify the origin of the lenticulostriate

perforators at their origin near limen insula.

22

Finally, the MCA should be exposed from its turn at the limen insula

distally to the segments at the surface of the peri-insular sulci.

3. Peri- insular sulcal dissection

Gliotic plane between the tumor and the surrounding white matter is best

identified at the base of the sulcus and hence, peri- insular sulcal dissection is

very important before the actual tumor decompression is started.

Inferior sulcus- between insula and the temporal operculum- is identified by

the large M2 vessels, which run parallel to the sulcus. Base of the sulcus has

insular vein, which can be coagulated.

Anterior sulcus- between insula and fronto-orbital operculum- is identified

by M2 branch supplying frontal lobe, which is usually present, but this sulcus

may be quite deep

Superior sulcus- between inusla and the fronto-parietal operculum­

dissection is difficult as MCA vessels run perpendicular to it rather than

parallel, as in inferior sulcus.

4.Division of short insular branches

There are three types of M2 perforators. The short and medium perforators

supply the insular cortex, the external capsule. claustrum and the extreme

-capsule. They have to be coagulated and divided individually. It is critical to

devascularize the tumor prior to actual resection. This is the most tedious

aspect of the operation, but careful dissection reduces the potential for injury

and actually saves time in the long run.

23

In contrast to the short and medium perforators, long perforators usually

arise in the posterior aspect of the insula. They make up less than 5 % of

perforators, but are critical because they supply the corona radiata and fiberes

of cortico-spinal tract. They are generally of larger diameter and arise from M2

branches overlying posterior insula.

5. Resection of the tumor mass

Once boundaries of insula are defined and the tumor is devascularised,

tumor is removed piecemeal in- between the vessels.

The biggest problem is determining where to stop the medial resection.

Peri-insular sulci often define the deepest plane of tumor. In addition, the most

distal lateral lenticulostriate vessels may mark the location of the medial tumor

border. Direction of perforators can offer a clue, as the vessels that run

parallel to the me,dial surgical bed are probably lenticulostriate perforators.

Posterior portion is critical, because the posteroinferior aspect of the tumor

lies near receptive speech areas in the temporal lobe and the posterosuperior

aspect of the tumor is close to the rolandic area of the frontal lobe; retraction

in these areas should be minimal.

Postoperative Neurological deficits and their avoidance

insula exerts an influence over a variety of neurological functions. Although

neuropsychological dysfunction has been reported to be associated with

resection of tumors of the insula, the most devastating insults involve motor

and speech dysfunction.

24

Direct stimulation of the tumor-infiltrated insula did not elicit motor

movements or speech arrest in the study by Lang 18. However, Duffau 17 noted

speech arrest on stimulation of anterior insula. Lang argues that, although

resecting insular tumors·may result in deficits because of specific functions of

insula, the avoidable complications are more related to disruption of the

surrounding structures and their vascular supply18.

Opercular retraction

A significant amount of retraction of frontal operculum is required to reach

superior peri-insular sulcus via a trans-sylvian approach. This may result in

motor dysfunction or speech dysfunction if the tumor is in the dominant

hemisphere, because Broca's area is located near the anterior insula point. In

addition, retraction may compress the M3 branches and result in frontal lobe

ischemia. Repositioning of frontal retractor restored speech function in two

patients who were awake during craniotomies in Lang's series 18. Similar

speech dysfunction may occur also due to temporal lobe retraction.

Yasargi116 recommends abandoning retractors and preferred using cotton

balls, which swell up and keep the sylvian fissure open.

Lang 18 suggested modification of trans-sylvian approach to include

resection of frontal operculum to avoid retraction, particularly in large tumors

of non- dominant hemisphere. Similarly temporal operculum may be resected

for predominantly temporal tumors.

He suggested using awake craniotomy to avoid complications related to

manipulation of surrounding structures.

25

MCA dissection

MCA is particularly vulnerable during removal of an insular tumor because

the tumors typically envelop the MCA and obscure it from the view.

Multiple small perforating vessels arise from undersurface of M2 and

provide blood supply to the tumor. Yasargil16•21 emphasized that each of these

insular vessels must be individually identified and coagulated to devascularize

the tumor. Thus, even if the parent vessel is preserved, the manipulation

required during coagulating these small perforators may cause MCA spasm

and postoperative deficits.

Lang 18 suggests identification of M1 medial to limen insula and to follow all

its branches over the surface of insula to avoid inadvertent injury to MCA. He

also recommends subpial dissection while coagulating small insular vessels

from M2 to minimize MCA manipulation.

Perforating vessel injury

All reports in literature emphasize that the lateral lenticulostriate arteries

(LLAs) are important source of complications because they supply the internal

capsule. Although these arteries do not supply the insula normally, insular

tumors may "parasatize" the LLA's as suggested by Lang 18.

______ Coagulation of LLA's that supply the internal capsule is reported to be a

major cause of postoperative hemiplegia in most series. Avoiding injury to the

LLA's that supply internal capsule is the major challenging aspect of insular

tumor surgery. Lang recommends identifying the most lateral LLA early in the

26

operation and defining a parasagittal plane, through which these vessels

course, to mark the depth of resection.

Another source of vascular injury to motor fibers is the long perforating

arteries arising from M2. Yasargil16•21 emphasized that these vessels most

commonly arise from the posterior M2 branches. It is recommended by Lang

to preserve any large perforating branches arising from M2 in the posterior

insula, particularly vessels that do not taper.

Internal capsule

The corticospinal tract is susceptible to direct injury just deep in relation to

the superior peri-insular sulcus, where it is not protected by the basal ganglia,

and dissection along the superior margin of many insular tumors can result in

hemiparesis. Lang suggests that if dissection is limited to the base of this

sulcus, interruption of the corticospinal tract can be avoided.

Zentner5 proposed two intraoperative aids- stereotaxy and somatosensory

and motor evoked potentials. Vanaclocha23 reported using awake craniotomy

and asking the patient to perform motor tasks to prevent damage to internal

capsule. He found the intraoperative ultrasound to be useful to delineate the

tumor margins, though it becomes difficult to differentiate tumor margin and

abnormal brain tissue induced by surgical manipulation. Ebeling 1 used

intraoperative histological cryo cut examination to confirm total resection but it

is time consuming. Duffau and associates 17 used intraoperative subcortical

electrical stimulation as a direct method to identify the internal capsule.

27

Selection of patients and grade of tumor

For low-grade gliomas (World Health Organization (WHO) grade II

astrocytomas, and oligodendrogliomas24), the role of radical resection is

controversial. Dilemma is greater for cases of insular gliomas, where

complete resection is difficult and risk of neurological morbidity is high.

However, Lang 18 argues than more extensive tumor resection will increase

patient survival. Also, in other studies on low-grade gliomas, extent of

resection is noted as a major predictor of survival.

Zentner suggested that beyond a reduction in mass effect, surgery might

provide little benefit for elderly patients with glioblastomas. However, some

other studies indicate improvement in survival with incremental increases in

resection 18•25.

28

RESULTS

In the time duration between October 1998 and June 2005, 69 cases of

insular tumors were admitted in our institute.

The lesion was left sided in 44 (63.8%) patients and right sided in 25

(36.2%) patients.

Clinical features:

The age of the patients ranged from 14 years to 66 years. Average age at

presentation was 39 years. Thirty- five patients (50.7%) were less than 40

years of age. The median age was 33.5 years for low-grade tumors and 41

years for high-grade tumors. There were 47 (68.1 %) males and 22 (31.9%)

females. Two patients (2.9%) had multiple neurofibromatosis (NF-1).

Seizures were the most common presenting complaint with 42 patients

(60.9%) presenting with various forms of seizures. Headache was second

most common presentation (18 patients; 26.1%) followed by cognitive decline

(7 patients; 10.1 %) and limb weakness (2 patients; 2.9%) (Table No. 1;

Chart No. 1 ).

-is/

Figure 1 - Photomicrographs of CA1 sector of hippocampus: sparse neurons (n) and reactive gliosis (rg) without corpora amylacea (MTLE-HS-CoA-)

Figure 2 - Photomicrographs of CA1 sector of hippocampus: grade 1, corpora amylacea deposition (MTLE - HS CoA + Grade 1)

61

Figure 3 - Photomicrographs of CA1 sector of hippocampus: grade 2, corpora amylacea deposition (MTLE - HS CoA + Grade 2)

Figure 4 - Photomicrographs of CA1 sector of hippocampus: grade 3, corpora amylacea deposition (MTLE - HS CoA + Grade 3)

62

30

Table No. 1. Presenting complaints

Presenting complaint N %

Seizwes 42 60.9

Headache 18 26.1

Cognitive decline 7 10.1

Limb weakness 2 2.9

Seizure was the most common symptom with 49 patients (71%)

presenting with various forms of seizures. Average duration of seizures was

26 months. Twenty- two (44.9%) had seizures of more than six months

duration. Most common type of seizure was generalized tonic-clonic seizures

(GTCS) (18; 37%), followed by complex partial seizures (CPS) in 13 (27%).

Other seizure types and their frequency of occurrence are shown in Table 2.

Four (8.2%) of the patients had ictal drooling of saliva, which is considered as

a visceral manifestation. Thirty-five patients with seizures (71.5%) had tumors

in left (dominant) hemisphere. The predominance of seizures in tumors of left

hemisphere was statistically significant (p=0.038; l test).

31

Table 2. Seizure tvpes and their incidence

Seizure tvQe N %

Generalised tonic-clonic seizures 18 37 (GTCS)

Complex partial seizures (CPS) 13 27

Focal seizures 5 10

CPS with secondary generalization 2 4

Focal seizures with secondary 4 8 generalization

GTCS and CPS 6 12

GTCS and focal seizures 1 2

Total 49 100

Thirty-nine patients (56.5%) had headache at initial presentation with an

average duration of 17 months. Seventeen patients with headache had

features of raised intracranial pressure. Twenty- three (33.3%) had headache

lasting less than six months.

Eleven patients had behavioral disturbances and an equal number had

impairment of memory at presentation. Average duration of behavioral

disturbance was 2.5 months and of memory impairment was 3.6 months.

On examination, 23 (33.3%) had features of raised ICP in the form of

papilloedema.

Seventh nerve paresis was present in 13 patients (18.8%) and two patients

had sixth nerve deficits. One patient had involvement of both sixth and

seventh nerves.

32

Eleven patients had hemiparesis and one patient had hemiplegia at

presentation. Two had faciobrachial weakness.

Dysphasia was present in six of the patients (13.6% of left sided tumors).

Imaging characteristics:

CT head was done in 67 of 69 patients. Tumors were predominantly

hypodense (47 cases; 71%) or isodense to hypodense (10 cases; 15%). CT

characteristics are shown in Table No.3. 75% of tumors were diffuse (50

cases) with no clear borders from surrounding brain tissue and 25% (17

cases) were focal lesions. The size ranged from 2.6cm as smallest dimension

and largest dimension was 7.5cm, among the scans for which measurements

were available. The extent of tumors into frontal, temporal and parietal regions

as noticed during surgery did not correlate with preoperative CT scans.

33

Table No.3. CT Characteristics

CT characteristics N %

Hypodense 47 71

Hyperdense 1 1

lsodense 5 7

lsodense to hypodense 10 15

lsodense to hyperdense 4 6

CT not available 2

Total 69 100

Mass effect on CT scan was seen in 17 cases (25.4%) and perilesional

edema in 37 cases (55.2%). 30 tumors (45.4%) were enhancing with contrast

out of 66 for which contrast studies were available.

MRI studies wee available in 57 cases. Lesions were predominantly

hypointense on T1 and hyperintense on T2. Tumors were diffuse with no

clear line of demarcation of tumor from adjacent tissue in T2 weighted images

in 37 cases (64.9%) and focal in 20 cases (35.1%). Maximum diameter was

8.3cm and the smallest diameter was 3.7cm among cases for which

measurements were available. As with CT scans, the extent of tumors into

frontal, temporal and parietal regions seen in MRI did not correlate well with

the findings during surgery.

MRI showed evidence of mass effect in 47 (82.5%) cases. Perilesional

edema was present in 29 (50.9%) cases. Twenty- eight (50.9%) of 55 tumors

34

for which contrast studies were done, showed enhancement. Predominance

of contrast enhancement was noted among high-grade tumors, with 11 of 15

high-grade tumors enhancing with contrast (p= 0.144).

Three tumors showed calcified lesions. Two of them were

oligoastrocytoma and one was astrocytoma grade II.

Tumors were classified according to the scheme proposed by Ozyurt26 into

various types depending on insular, opercular, paralimbic and limbic

structures involvement. Majority of tumors were of Type 2, that is tumors

involving the insula and additionally operculae (30 cases; 52.6%). The

distribution into various types is shown in Table No.4 and Chart No.3.

Table No.4 Classification based on MRI characteristics (0zyurf6)

Type N (57) %

1 (tumor restricted to insula) 6 10.6

2 (tumor involving the insula and additionally 30 52.6

operculae)

3a (insula, operculum and one paralimbic 2 3.5

involvement)

3b (insula, operculum and both paralimbic 11 19.3 involvement)

4a (insula, operculum, limbic structures and one 4 7

paralimbic involvement)

· 4b (insula, operculum, limbic structures and both 4 7 paralimbic involvement)

36

Table No.5 Surgical a~~roach and extent of resection

N %

Decompressive surgery 65 94.3

Approach

A. Transsylvian 56 86.2

B. Temporal 3 4.6

C. Frontal 6 9.3

Total 65 100

Extent of resection

A. Sub-total decompression 56 86.2

B. Near-total decompression 9 13.8

Total 65 100

Among the patients who underwent decompressive surgery, initial step

was splitting the sylvian fissure all along in 56 cases (86.2%). In cases where

temporal extent of tumor is significant, temporal decompression was done as

the first step, prior to sylvian dissection (3 cases; 4.6%). Similarly, in cases

where frontal extension was more, frontal decompression was done before

approaching the insular mass (6 cases; 9.3%). The approach to the tumors is

shown in Table No.5 and Charts No.4 and 5 ..

38

Fifty-six patients underwent sub-total decompression of the tumor and

nine underwent near-total decompression. The decision to limit the resection

depended on intraoperative assessment of extent of tumor. Proximity to

internal capsule and encasement of MCA branches precluded further

decompression.

Twenty- four (36.9%) tumors involved insular region and additionally frontal

and temporal opercula. Combined insular and frontal involvement was noted

in 12 patients (18.4%) and combined insular and temporal involvement in 10

cases (15.4%). Pure insular tumors constituted 12.3% (8 cases). The

distribution of tumors according to intraoperative impression of its extent is

shown in Table No.6.

Table No.6. Extent of tumor; intra-operative impression.

Site N %

1 F+l 2 3.0

2 I 8 12.3

3 I+F 12 18.4

4 I+F+T 24 36.9

5 I+F+ T +CC+Opp.fr 1 1.6

6 I+F+T+P 3 4.6

7 I+T 10 15.4

8 I+T+P 1 1.6

9 I+T+F 2 3.0

10 T+F+P+I 1 1.6

11 T+l 1 1.6

12 NA 4

I= insular; T= temporal opercular; F= frontal opercular; P= parietal opercular; CC= corpus callosum; Opp.fr= opposite frontal lobe. Region predominantly involved as perceived during surgery is entered first, followed by next predominant site.

39

Temporal component of tumor was decompressed in 26 patients (40%)

who had temporal opercular or mesial temporal involvement. In 19 patients

(29.2%), who had involvement of frontal operculum, additional frontal

approach was used.

Temporal lobectomy was done in 29 patients (44.6%), who had significant

mass effect in pre-operative imaging.

Thirteen tumors (18.9%) had cystic and solid components. Mesial

temporal structures were involved in ten cases (14.5%). Basal ganglia were

involved in two cases. Nineteen patients (27.5%) had evidence of uncal

herniation during surgery.

Middle cerebral artery (MCA) (M2 or its perforators) were encased in 28

cases and splayed in four cases. Papaverine was successfully used to

reverse the spasm of MCA or its branches in eight cases.

On grouping the extent of tumors according to Yasargil's first three areas 16,

with the modification of including mediobasal temoral tumors with insular

extension in Area 1, we found a predominance of area 3 (Orbitofrontal­

insular-opercular-temporal pole tumors) tumors (51 cases; 73.9%). 11.6% (8

cases) were pure insular (area 2) tumors and 14.5% (1 0 cases) were

mediobasal tumors with insular extension (Table No.7).

40

Table No.7. Classification according to Yasargi116 (modified)

Area N (69) %

1 Area 1 (mediobasal temporal tumors

10 14.5 with insular extension)

2 Area 2 (pure insular tumors) 8 11.6

3 Area 3 (Orbitofrontal- insular-

51 73.9 opercular-temporal pole tumors)

Histopathology:

The histopathology showed glial neoplasm in 68 cases. One case had

metastatic adenocarcinoma of probable thyroid origin. Of the tumors that were

graded (54), majority (34; 63.0%) was of low grade. There were 44

astrocytomas, 13 oligoastrocytomas, one pleomorphic xanthoastrocytoma

(PXA) and one metastatic lesion in the series. The detail of grade of the

tumors and their histopathology is shown in Table No.8 and Chart No.6.

Table No.8 Histopathology of tumors

Grade24 Astrocytoma Oligoastr-

PXA Metas Total ocytoma -tasis Fibrillary Gemistocytic NOS

II 6 0 23 2 1 NA 32

Ill NA 2 12 4 NA NA 18

IV NA NA 2 NA NA NA 2

NOS NA 2 7 7 NA 1 17

Total 6 4 44 13 1 1 69

NOS- not otherwise specified; NA- not applicable; PXA- pleomorphic xanthoastrocytoma

42

in postoperative period. Another patient, who had MCA spasm during surgery,

did not resolve with papaverine, and developed hemiplegia postoperatively.

Table No.9. Complications and outcome

Pre-Deficits Post-operative

operative

New N %* Improved % Persisted % Worsensed % %*

Deficit

Seizures 49 71.0 29 59.2 20 40.8 0 0 2 2.9

Hemiparesis 10 14.5 2 20.0 4 40.0 4 40.0 7 10.1

Hemiplegia 1 1.4 0 0 1 100.0 0 0 1 1.4

Upper limb 2 2.9 2 100.0 0 0 0 0 1

weakness 1.4

7'h nerve 13 18.8 6 46.2 7 53.8 0 0 4 5.8 weakness

61h nerve 3 4.3 3 100.0 0 0 0 0 1 1.4 paresis

3rd nerve 0 0 0 0 0 0 0 0 2 2.9

paresis

Dysphasia 6 13.6** 4 66.7 2 33.3 0 0 8 18.2**

*=Percentage of 69 cases; **=percentage of left sided tumors (44 cases).

Upper limb monoparesis improved after surgery in both patients who had it

preoperatively. However, another patient developed fresh upper limb

monoparesis after surgery.

Of 13 cases who had seventh nerve weakness preoperatively, six (46.2%)

improved and seven (53.8%) persisted. Four patients developed seventh

nerve weakness postoperatively. Third nerve paresis was noted in the form of

asymmetric pupils and dilated ipsilateral pupil in two cases postoperatively.

44

Among six patients who had dysphasia and dominant hemispheric tumor

(13.6% of left sided tumors) preoperatively, four (66.7%) improved and two

had persistence of speech difficulty. Mild speech difficulty was noted in 8

cases (18.2% of left sided tumors) postoperatively, which was transient in

majority of cases.

Nineteen patients developed new deficits after surgery. The difference in

occurrence of new deficits after surgery on the right-sided tumors (5 cases)

and left sided tumors ( 14 cases) was noted (Table No.1 0), but was not

statistically significant (p=0.2908; x} test). However, on analyzing patients

who had no limb deficits or dysphasia preoperatively, new onset of

hemiparesis was noted in ten patients of whom nine were in dominant

hemisphere.

Table No.1 0 Incidence of various new deficits after surgery and their

laterality

New deficits after surgery N % Left Right

Seizures 2 2.9 1 1

Hemiparesis 7 10.1 7 0

Hemiplegia 1 1.4 0 1

Upper limb weakness 1 1.4 1 0

7th nerve weakness 4 5.8 3 1

.. 6th nerve paresis 1 1.4 1 0

3rd nerve paresis 2 2.9 1 1

Dysphasia 8 18.2* 8 0

Total 19 27.5 14 5

*=% Of left sided tumors

45

Duration of stay in the hospital varied from four days to 28 days, which

included variable periods of preoperative stay. Mean period of stay was

thirteen days.

Adjuvant therapy:

Fifty-nine patients, who had residual lesions or high-grade tumors in

histopathology, underwent radiotherapy. One patient underwent radiotherapy

after second surgery for recurrence. Three patients underwent chemotherapy

(two with anaplastic astrocyoma and one with grade II astrocytoma following

radiotherapy). One patient, who had pre-operative radiotherapy, underwent

chemotherapy postoperatively.

Surgical Outcome and follow up:

The measures of outcome in our series were defined by the amount of

residual tumor on postoperative CT imaging, neurological status at discharge

and at follow-up review and the progression-free survival.

Residual lesions:

Out of 67 patients who underwent postoperative CT scan before discharge

from the hospital, 53 (79.1 %) had evidence of residual lesion and only2.0.9%

had their tumors resected completely according to CT imaging standards. In

.. .. ___ _!bemajority of our cases, small amounts of residual tumor were seen. These

patients were referred for adjuvant radiotherapy if the amount of residual was

significant, even if histopathology showed a grade II tumor.

46

Neurological status at discharge:

Preoperative performance was categorized into three groups. The first

category included patients who had some symptoms and were able to carry

out normal activities with or without effort. This category corresponds to

Karnofsky Performance Score (KPS) of 80 to 1 00. Second category included

those who were unable to carry on normal activity and required occasional to

considerable assistance (KPS 50 to 70). The third category (KPS <40) is of

patients who are disabled and require special care and assistance27.

Forty-four patients (63.8%) had good recovery (KPS 80 to 100) and 16

(23.2%) had moderate disability (KPS 50 to 70). Nine patients (13.0%) had

KPS of less than 40 at discharge.

Follow up:

Except six patients, all patients had at least one follow up after surgery.

One patient who underwent stereotactic biopsy at another hospital followed by

radiotherapy, presented with increase in size of lesion and mass effect four

years later. He had frontal pole infarct after initial transsylvian near total

decompression and underwent frontal lobectomy one week later. His

histopathology showed oligoastrocytoma grade Ill. He had no hemiparesis or

speech disturbances postoperatively. Second patient who underwent subtotal

decompression of a grade II astrocytoma had aphasia and left caudate infarct

postoperatively. He was referred for radiotherapy, but he was lost for further

follow up.

47

Another patient who presented in altered sensorium and hemiparesis was

treated for suspected herpes simplex encephalitis at another hospital before

undergoing near total decompression of an oligoastrocytoma grade Ill. His

weakness worsened to hemiplegia postoperatively. Other three patients

underwent subtotal decompression of grade II (2 patients) and grade Ill (one

patient) astrocytomas and were referred for postoperative radiotherapy,

before they lost to follow up. The latter patient was a chronic narcotic addict

whose sensorium had improved postoperatively.

Among the remaining 63 patients who came for follow up in the outpatient

department, mean duration of follow up was 9.1 months. Five patients died in

follow up, after a mean overall survival of 25.30 months (Graph No.1).

Seventeen patients had recurrence of tumor in follow up. Their mean

progression- free survival was 20.69 months (Graph No.2).

49

Seizure outcome:

Out of 49 patients who had seizures preoperatively, 29 (59.2%) became

seizure free (Engel's score-1) and 20 (40.8%) had reduction in seizure

frequency (Engel's score-11 to Ill). Two patients who were seizure free

preoperatively had seizures postoperatively.

Factors affecting Progression-free Survival:

On analyzing various factors (age, sex, side of the tumor, mass effect as

seen on MRI, WHO grade, extent of resection, status of MCA during surgery,

preoperative performance score, postoperative performance score,

postoperative radiotherapy and chemotherapy}, only performance scores

were found to have statistically significant survival benefit (Table No.11; Chart

No.8).

In the group of patients with age less than or equal to 40 years, the mean

progession free survival (PFS) was 22.05 months, and in the group with age

above 40 years, the PFS was 17.43 months (p=0.8573). Female patients

appeared to have longer progression free survival than males. PFS in females

was 32.49 months and for males, it was 15.77 months (p=0.2471). Right-

sided tumors had PFS of 29.45 months and tumors in the dominant

hemisphere had PFS of 17.04 months (p=0.3944) (Graph No.3).

(

51

i

Table No.11. Factors affecting the Progression- Free Survival {PFS}

Factor N n* % Mean PFS P value in months (log rank

test) I~ • \'

Age <40yrs 35 12 50.7 22.05 0.8573

>40yrs 34 5 49.3 17.43

Sex Male 47 12 68.1 15.77 0.2471

Female 22 5 31.9 32.49

Side Right 25 5 36.2 29.45 0.3944

Left 44 12 63.8 17.04

Pre-operative 80-100 47 13 68.1 25.26 0.0140 Performance Score (KPS) at 50-70 18 3 26.1 6.36 presentation

<40 4 1 5.8 4.20

Mass effect Yes 47 11 82.5 18.08 0.1488

No 10 3 17.5 41.31

WHO grade II 34 9 63 28.11 0.1972

Ill, IV 20 4 37 13.72

Extent of Subtotal 56 11 86.2 21.79 0.9606 resection

Near total 9 3 13.8 19.71

Performance 80-100 44 14 65.2 23.81 0.0554 score at discharge 50-70 16 2 23.2 7.05

<40 9 1 11.6 4.20

MCA status Encased/ 30 6 43.5 18.86 0.7807 spasm

Splayed/ 39 11 56.5 21.69 displaced

- --------- ----- - - ---- ~ ~

Radiotherapy Yes 59 16 85.5 21.62 0.1326

No 10 1 14.5 5.73

Chemotherapy Yes 3 1 4.4 6.20 0.2359

No 66 16 95.6 21.59

*n= number of recurrences

52

Graph No.4 Kaplan- Meier curves demonstrating median time to recurrence from surgical diagnosis according to the preoperative performance score.

1,0

Progression-free Survival

Pre-operative KPS

0 20 40 60

Progression- free interval in months

80

KPS1

• KP$80-100

Q KP$50-70

• KP$<40

100

Graph No.5 Kaplan- Meier curves demonstrating median time to recurrence from surgical diagnosis according to the performance score at discharge

Progression- free Survival

KPS at discharge 1.0

.8

.6

0 20 40 60

Progression-free interval in months

KPS at discharge

• KP$80-100

.. KP$50-70

• KP$<40

100

53

Absence of mass effect as seen on MRI showed no significant survival

benefit, though in the group with mass effect, the PFS was 18.08 months and

in those who had no mass effect, it was 41 . 31 months (p=O .1488).

Among the low-grade tumors (WHO grade II), the PFS was 28.11 months,

and in high-grade tumors (WHO grade Ill and IV), it was 13.72 months (p=

0.1972) (Graph No.6).

Cases who underwent near- total decompression had PFS of 19.71

months and those who underwent sub-total decompression had a PFS of

21.79 months (p= 0.9606). This apparent disparity (Graph No.7) was analyzed

further and was found because of higher proportion of high-grade tumors

among the group who underwent near- total decompression. This shows the

difficulty to achieve near-total decompression in low-grade tumors, because of

lack of well-defined borders and subsequent difficulty to judge the medial

extent of resection. When analyzed separately for high- and low-grade

tumors, near total decompression had definite survival advantage over sub­

total decompression, though not statistically significant.

Encasement of MCA during surgery or spasm of MCA or its major divisions

had no effect on progression free survival (p= 0.7807).

54

Graph No.6 Kaplan- Meier curves demonstrating median time to recurrence from surgical diagnosis according to the grade of the tumor. Low grade= WHO grade II: High grade= WHO grades Ill and IV.

1.0

.8

.6

Progression-free Survival

Histopathological grade of the tumor

0 20 40 80

Progression-free interval in months

80

HPRgrade

WHO grade II

" WHO grades Ill, IV

100

Graph No.7 Kaplan- Meier curves demonstrating median time to recurrence from surgical diagnosis according to the extent of resection.

Progression- free Survival

Extent of Resection

·: n L,.-

.6

~ '2:: .4

iil Decompression ~ 2

113 "5 Near total § 0 0.0 +------'-....-----.---.,.._ __ " Sub-total

100 0 20 40 80 80

Progression- free interval in months

56

Adjuvant therapy:

All patients who had high-grade lesions (grade 3 or 4) or significant

residual lesions were referred for postoperative radiotherapy. Six patients who

had low-grade tumors with no obvious residual lesion in immediate

postoperative CT scan were also sent for radiotherapy at the discretion of the

operating surgeon, depending on his intraoperative assessment of residual

lesion. Thus, a total of 59 (85.5%) patients underwent radiotherapy. Mean

progression free survival among patients receiving radiotherapy was longer

(22.97 months) compared to those who did not receive radiotherapy (6.23

months; p=0.1326).

Mean progression free survival was 7.57 months in three patients

receiving chemotherapy, whereas it was 22.88 months among those not

receiving chemotherapy.

Recurrence:

Seventeen patients had recurrence of lesion during follow up. Average

progression-free interval was 21 months. Six patients underwent surgical

decompression of the recurrent lesion. Histopathology of reoperated cases

showed two anaplastic astrocytomas and one oligoastrocytoma grade Ill. One

of these three gliomas had progressed from WHO grade II to grade Ill in the

second surgery. Two gliomas that recurred were not graded. One 14 year-old

boy with pieomorphic xanthoastrocytoma undervvent decompression of

recurrence six months after the first surgery.

57

DISCUSSION

With the inherent difficulties of operating on the insula and its subsequent

morbidity, surgical resection was not a favored option for insular tumors till

quite recently. However, the recent advances in microsurgical techniques and

insular anatomy prompted us to perform microsurgical resection of insular

tumors, which form a significant proportion of cases in our tertiary referral

center. Our enthusiasm was reinforced by the large series of Yasargil16, which

demonstrated the efficacy of highly skilled microneurosurgery.

Our series of 69 cases span over a period of about seven years and was

operated upon by various surgeons using microneurosurgical techniques.

Thus, the outcome was dependant on various factors including availability of

MRI and the surgeons' learning curve.

At present, there is no protocol set for management of insular tumors at

our institute and decision regarding optimum surgical resection depends on

the surgeons who assess the case individually.

The analysis of results from this series hopes to identify the risk factors for

complications and outcome, mortality and morbidity statistics and to aid in

development of a standard protocol for management of tumors involving

the insula.

Clinical features:

Our series of 69 cases of insular tumors form one of the largest series

reported on their surgical management in literature. Apart from the classical

58

report of Yasargil16 , large studies on surgical resection of insular tumors are

few. In the series of Yasargil, the insular involvement was present only in Area

2 and 3 tumors, which constituted 80 cases.

Insular tumors had a preference to the dominant (left) hemisphere in our

series. The lesion was left sided in 44 (63.8%) of our patients and right sided

in 25 (36.2%). This preferential involvement is noted in other series also.

Yasargil's series had 53.1% of left sided tumors. Vanaclocha et aJ23 noted left

sided tumors in 69.6%, and Lang et al18 in 59.1% of their cases. However,

series from Ozyurt26 and Duffau 17 showed predominance of right sided tumors

(37.5% and 16.7% respectively).

Left sided tumors presented with seizures more often (79.5%) of and this

predominance of seizures in tumors of left hemisphere was statistically

significant (p=0.038; ,.l test). 64.7% of left sided tumors and 60% of right

sided tumors were of low grade; p=0.7262; x2 test).

The age of the patients ranged from 14 years to 66 years. Average age at

presentation was 39 years. The mean age ranged from 27 to 43.6 years in

various series and is in accordance with the present study. Thirty- five

patients (50.7%) were less than 40 years of age. The median age was 33.5

years for low-grade tumors and 41 years for high-grade tumors. 71% of

tumors in younger age group (<40 years) were of low grade (p=0.1573; x2

test). This suggests the preferential involvement of insula by low-grade glioma

in younger patients.

There were 47 (68.1 %) males and 22 (31.9%) females. Several other

59

series5•23 show male preponderance in their studies.

Two patients (2.9%) had multiple neurofibromatosis (NF-1). Both had

multiple subcutaneous nodules and cafe au lait spots. The significance of NF-

1 with limbic or paralimbic glioma was not analyzed in any other studies. One

patient who had a small tumor, with associated NF-1 was initially managed

conservatively, after evaluation for an episode of generalized seizures. He

was asked to be in close follow-up. Unfortunately, there was progression of

disease within three months and he presented with hemiplegia and aphasia.

He underwent decompression of the insular tumor and histopathology showed

high-grade glioma. Other patient underwent decompression of an

oligoastrocytoma. It is therefore, prudent not to extrapolate the benign

association of NF-1 and optico-chiasmatic gliomas to insular gliomas, till

further studies are available.

Seizure was the most common symptom with 49 patients (71%)

presenting with various forms of seizures. Seizures are the predominant

symptom in all the studies on insular gliomas as shown in Table. Thirty-five

patients with seizures (71.5%) had tumors in left (dominant) hemisphere. The

predominance of seizures in tumors of left hemisphere was statistically

significant (p=0.038; -l test).

60

Table No.12. Presenting symptoms in various studies on surgical resection of insular tumors

Stud~ Year N S~m11,toms (%l

Focal deficits Seizures (Hemiparesis/ Headache Cognitive

weakness) decline

Yasargil16 1992 177 77 21 NA 44.1

Zentner5 1996 30 63.3 30* NA 6.7

Duffau17 2000 12 100 0 NA NA

Lang18 2001 22 64 32 NA NA

Ozyurt26 2003 40 62.5 NA 7.5 NA

Present 2005 69 71 27.5 56.5 15.9 Study

*aphasia included with focal deficits

Dysphasia

(% Of left sided tumors)

33

*

NA

18

NA

13.6

High incidence of seizures as the presenting symptom is noted in all the

studies (Table No.12). 77% of Yasargil's patients had seizures as the

presenting complaint and the incidence varied from 62.5 to 64% in other

series. Yasargil16 noted a predominance of CPS in his cases, but GTCS was

the most common seizure type in our series (Table No.13). None of our

patients presented with status epilepticus, though Yasargil reported one such

case in his study.

61

Table No.13. Predominant seizure types in present series compared with

Yasargil's series

Present Yasargil, series 199216

Seizuretme N % N %

Generalised tonic-clonic seizures (GTCS) 18 37 22 16

Complex partial seizures (CPS) 13 27 66 48

Simple partial seizures 5 10 9 6.5

CPS with secondary generalization 2 4 15 11

56.5% of the patients had history of headache at presentation. Seventeen

patients with headache had features of raised intracranial pressure. In

Ozyurt's study26, the incidence of headache was lesser (7.5%) and headache

was not a presenting symptom in other series. This may be the result of

relatively larger tumors and mass effect in the present series.

15.9% had history of behavioral disturbances and an equal number had

impairment of memory at presentation in present study. In Zentner's study5,

6.5% had a psycho-organic syndrome. Yasargil16 noted neuropsychological

defect in 78 of his 177 cases. But most of them (50) were tumors limited to

mediobasal temporal region, which is not included in present study. Excluding

the mediobasal lesions, the incidence of neuropsychological deficits is 35%,

which is still significantly higher than in the present study.

Focal deficits in the form of hemiparesis, hemiplegia, facial or faciobrachial

weakness were noted in 27.5% of our cases. Lang18 noted focal deficits in

62

32% of his series whereas the incidence of focal deficits was 21% in

Yasargil's series. Again, if mediobasal tumors were excluded in Yasargil's

series, the incidence of sensorimotor deficits rose to 26.2%, which is

comparable with our study.

Dysphasia was present in six of the patients (13.6% of left sided tumors).

Incidence of dysphasia is comparable with Lang's series where it was 18% of

left sided tumors. Yasargil noted a 33% incidence of speech disturbances in

left hemispheric tumors, which manifested as "word finding" difficulty. Such

characteristic speech disturbance, which is clearly not classical expressive,

receptive or conductive aphasia, was noted in our patients. Excluding

mediobasal tumors, the incidence of dysphasia in Yasargil's study rose to

50%. Lesser incidence in the present series may be due to milder degrees of

speech disturbances, which would have been detected using detailed

preoperative speech evaluation.

42% of our patients had no neurological deficits (no limb weakness, cranial

nerve deficits, dysphasia, behavioural disturbances, memory impairment or

papilledema) at presentation. Yasargil had 37.5% of such patients with no

deficits in the comparable group. Papilledema was noted in 33% of our cases,

whereas it was present only in two out of 80 cases (2.5%) in Yasargil's

comparable group. This may suggest the relatively larger tumors with mass

effect in the present series.

Imaging characteristics:

The extent of tumors into frontal, temporal and parietal regions as noticed

63

during surgery did not correlate with preoperative CT scans. Hence, most of

the studies preferred preoperative MRI to plan the resection.

Tumors were diffuse with no clear line of demarcation of tumor from

adjacent tissue in T2 weighted images in 37 cases (64.9%) and focal in 20

cases (35.1 %). Lang 18 reported sharp borders of the tumor in 54.5% of his

cases and diffuse lesions in 45.5% of cases. In Ozyurt's series26, tumors were

well demarcated in 72.5% of cases and infiltrative in 27.5%. Tumors with

diffuse margins on T2 weighted imaging are generally considered less

amenable to near total resection, because the interface between the tumor

and the brain is often difficult to define. However, in our series, near total

decompression was possible in 11% of diffuse tumors and 15% of focal

tumors, the difference of which is not statistically significant (p=0.6456; r.}

test). As with CT scans, the extent of tumors into frontal, temporal and parietal

regions seen in MRI did not correlate well with the findings during surgery.

Predominance of contrast enhancement was noted among high-grade

tumors, with 11 of 15 high-grade tumors (73.3%) enhancing with contrast (p=

0.144; x2 test). Significantly, 50% of low-grade tumors were also enhancing

with contrast. Contrast enhancing tumors had a mean progression free

survival of 14.57 months, whereas non- enhancing tumors had a better

survival of 29.42 months (p=0.27 43; log-rank test). Contrast enhancement is

considered as a poor prognostic indicator for prolonged survival for gliomas in

general, irrespective of the site. Our study concurs with the available

literature28 in this issue.

64

The classification of insular tumors according to its extent in MRI, as

proposed by Ozyurt26, was adopted in our series. However, the surgical

approach to majority of the tumors was guided by its gross extension into the

opercula, rather than the type of tumor according to Ozyurt. This is probably

due to relatively large size of tumors in the present study and also due to

predominance of insula- opercular (Type 2) tumors rather than a paralimbic

(Type 3) or limbic (Type 4) involvement as was seen in Ozyurt's study (Table

No.14).

Table No.14. Ozyurt's types on MRI

Tumortyr,e Ozyurt series Present (Ozyurf') (%) series(%)

Type 1 17.5 10.6

Type2 20.0 52.6

Type 3 37.5 22.8

Type4 25.0 14.0

Surgery:

Transsylvian fissure approach is the optimal method of exploration for

removal of an insular lesion. This approach was used in majority (56) of our

cases (86.2% ). Transopercular exploration and removal of an insular glioma is

indicated only in rare cases, when the tumor encroaches on adjacent frontal

or temporal operculum. However, Yasargi116 suggests that achieving an initial

gross total resection of the tumor in the opercular area considerably facilitates

further opening of the sylvian fissure, permitting effective removal of the

65

insular part of the glioma. Further, such opercular decompression will reduce

the need for retraction and reduces the morbidity associated with it. In present

study, frontal decompression was done before approaching the insular mass

in 6 cases (9.3%) and temporal decompression was done in 3 cases (4.6%) to

aid in approach to the insula.

The major problems during surgery included detection of the internal

capsule and preservation of the lenticulostriate arteries.

The extreme capsule and the claustrum protect the internal capsule. These

structures can be identified with operating microscope, and they represent the

limit of resection. We found a distinct granular appearance of these structures

under the operating microscope and used it as a guide to limit the resection

and to avoid injury to the internal capsule. Yasargil21 noted a similar finding of

a distinctive beige hue of striatal nuclei medially. His description of basal

ganglia as having the appearance of a nutmeg, with white stripes and dots of

beige colour, which indicate the soft tissue of claustrum, putamen and

amygdala, was typically noted in some of our patients. Such an appearance is

not highlighted in other studies.

Intraoperative spasm of the MCA or its major branches was noted to be a

significant factor leading on to increased morbidity. MCA spasm could be

successfully reversed using papaverine soaked cottonoids in eight of our

patients. Yasargil16 also reports intraoperative use of papaverine to reverse

MCA spasm. However, one of our patients developed hemiplegia following

MCAspasm.

66

Histopathology:

The histopathology showed glial neoplasm in 68 cases and metastatic

adenocarcinoma of probable thyroid origin in one case. Of the tumors that

were graded (54), majority (34; 63.0%) was of low grade. In Yasargil's study16,

35 (43.7%) out of 80 comparable tumors were benign (low grade). The benign

group constituted 56.5%, if mediobasal temporal tumors were included. The

proportion of low grade and high-grade tumors in various studies is compared

in Table No.15. Overall, a tendency for tumors to the insula to be of low-grade

can be noted.

Table No.15. Comparison of histopathological grades in various series

Low High Study N grade % grade %

tumors tumors

rtasargil16 80 35 43.7 45 56.3

Zentner 30 15 50 15 50

Vanaclocha23 23 16 69.6 7 30.4

Duffau 17 12 12 100 0 0

Lang 18 22 11 50 11 50

Ozyurt26 40 25 62.5 15 37.5

Present study 69 34 63 20 37

Complications and outcome:

There were no deaths related to surgery among the entire series of 69

patients, similar to previous reports.

67

Among the nineteen patients who developed new deficits after surgery, the

difference in right-sided tumors (5 cases) and left sided tumors (14 cases)

was noted, but this was not statistically significant (p=0.2908; x2 test).

However, on analyzing patients who had no limb deficits or dysphasia

preoperatively, new onset of hemiparesis was noted in ten patients of whom

nine were in dominant hemisphere. This contradicts the general notion that

the decompression tends to be more aggressive on non- dominant side

leading to higher incidence of deficits after resection of right-sided tumors.

Such a difference in occurrence of postoperative fresh deficits in right and left

sided tumors is not highlighted in other reports.

Immediate postoperative deficits were noted in a significant number of

patients in various studies. Postoperative deficits of hemiparesis and

dysphasia occurred after six (21 %) of 28 surgeries in Vanaclocha's series23.

Zentner et al. 5 reported complicated postoperative course in 63% of their 30

patients. Hemiparesis occurred in three (21 %) of 14 left sided tumors.

However, only three had persistent focal deficit. 58% of 12 cases displayed an

immediate postoperative deficit in series reported by Duffau and associates 17.

One of the two patients with dominant hemisphere tumors experienced

transient dysphasia and 60% had motor deficits. However, only one had

permanent weakness after three months.

In the series by Yasargil and colleagues 16 eight (14%) of 57 patients with

purely insular or insular-opercular and one (4%) of 23 patients with insular

and frontal- temporal pole tumors achieved a "moderate" outcome, which was

' .• l

68

defined as requiring assistance because of hemiparesis. Postoperative

speech dysfunction was not reported.

Seizure outcome:

In the Yasargil's series 16, among 62 tumors involving areas 2 and 3 who

had preoperative seizures, 90.3% were seizure-free postoperatively and 9.7%

had worthwhile improvement (Engel's score Ill). However, in the present

series, out of 49 patients who had seizures preoperatively, 29 (59.2%)

became seizure free (Engel's score-1) and 20 (40.8%) had reduction in

seizure frequency (Engel's score-11 to Ill). Two patients who were seizure free

preoperatively had seizures postoperatively. The sub optimal outcome

regarding seizure outcome in the present series may be due to the significant

proportion of cases having residual lesions. The extent of resection was not

reported in Yasargil's series, though presumably, radical resection was

achieved in their cases.

Factors affecting Progression-free Survival:

Survival and outcome analysis of insular gliomas after microsurgical

resection has not been reported in other series. However, an attempt was

made in the present study to analyse the factors affecting the progression-free

survival after surgical resection of insular gliomas. On analyzing various

factors (age, sex, side of the tumor, mass effect as seen on MRI, WHO grade,

extent of resection, status of MCA during surgery, preoperative performance

score, postoperative performance score, postoperative radiotherapy and

chemotherapy), only performance scores were found to have statistically

69

significant survival benefit. This concurs with the survival studies on gliomas

in general, irrespective of site28 .

Residual tumor:

Some studies 1 have recommended reoperation if any residual tumor is

seen in a MRI two days after the surgical procedure, unless they lie close to

the corticospinal tract. Regular follow up is another option23 with reoperation in

case of recurrence. We followed up the patients with residual tumors and

most of them received postoperative radiotherapy. Those who developed

significant increase in size of residual lesion suggestive of recurrence, or

neurological deterioration during follow-up underwent second procedure for

decompression.

With the strict measures applied, out of 67 patients who underwent

postoperative CT scan before discharge from the hospital, 53 (79.1 %) had

evidence of residual lesion and only 10.9% had their tumors resected

completely according to CT imaging standards. In the majority of our cases,

small amounts of residual tumor were seen. The significant number of

residual lesions seen in our study (79.1 %) is attributable to the predominantly

large size of the tumors and close proximity to corticospinal tract. In addition,

postoperative changes are difficult to differentiate from residual tumor in

immediate postoperative CT scans.

In many studies, the results of surgery with regard to amount of tumor

excised remains dismal, when assessed by the objective criteria such as MRI.

High-grade tumors had the highest ratio of "radical" removal according to

70

CT imaging criteria reflecting the fact that the differentiation between

tumorous tissue and tumor-free white matter is much more difficult in low­

grade tumors and thus it is in these cases that residual tumor is left behind.

The phenomenon that gross radiographic removal of low-grade intrinsic

tumors is hardly ever achieved is generally observed in all gliomas regardless

of location. Thus, our ratio of the radical extent of excision is not related to the

critical location of the lesions.

Recurrence:

The tendency of recurrent tumors to occur within the same functional and

anatomical area from which they arose, and remain within the same

allocortical or mesocortical zones as pointed out by Yasargil16, was noted in

all the 17 patients who had recurrence of lesion during follow up.

Adjuvant therapy:

All patients who had high-grade lesions (grade 3 or 4) or significant

residual lesions were referred for postoperative radiotherapy. 59 (85.5%) of

patients underwent radiotherapy. Mean progression free survival among

patients receiving radiotherapy was longer (22.97 months) compared to those

who did not receive radiotherapy (6.23 months; p=0.1326).

Mean progression free survival was 7.57 months in three patients

receiving chemotherapy, whereas it was 22.88 months among those not

receiving chemotherapy. This finding is likely to be biased because

chemotherapy was considered for particularly poorer grade residual tumors.

• ..

71

CONCLUSIONS

1. Insular gliomas can be resected by microsurgery with an acceptable

morbidity and to as radical an extent as possible.

2. Seizures are the most common presenting symptom and may be cured

after tumor resection.

3. Lesions located in the insular region are predominantly of low-grade.

4. In order to decrease the rate of complications, a standard pterional

approach, splitting the sylvian fissure along its full length is used. The

important points to remember during this operative procedure include

identifying carefully the periinsular sulci and the lenticulostriate vessels,

carefully protecting the middle cerebral artery, careful identification of

medial limit of tumor and minimizing retraction of the frontal and

temporal opercula.

5. A distinct granular appearance of extreme capsule and the claustrum

under the operating microscope was found to be useful as a guide to

limit the resection and to avoid injury to the internal capsule. Caution

during dissection at the uncinate fasciculus is warranted to avoid injury

to lenticulostriate vessels.

72

6. Outcome analysis suggested survival benefit to patients with good

preoperative performance status.

7. Results of our study demonstrate that resection of intrinsic insular

tumors is feasible. Although the risks are not insignificant, neurological

complications can be reduced and the extent of resection can be

maximized, with a good understanding of the surgical anatomy and an

awareness of the potential pitfalls.

73

REFERENCES

1. Ebeling U, Kothbauer K. Circumscribed low-grade astrocytomas in the

dominant opercular and insular region: a pilot study.

Acta Neurochir (Wien). 1995;132(1-3):66-74.

2. Ture U, Yasargil DC, AI-Mefty 0, Yasargil MG. Topographic anatomy of

the insular region J Neurosurg. 1999 Apr;90(4):720-33.

3. Varnavas GG, Grand W; The insular cortex: morphological and vascular

anatomic characteristics. Neurosurgery. 1999 Jan; 44(1 ): 127 -36;

4. Tanriover N, Rhoton AL, Kawashima M, Ulm AJ, Yasuda A. Microsurgical

anatomy of the insula and the sylvian fissure. J Neurosurg 2004; 100:891-

922.

5. Zentner J, Meyer 8, Stangl A, et al. Intrinsic tumors of the insula: a

prospective surgical study of 30 patients. J Neurosurg 1996;85:263-271.

6. Yasargil MG, Krisht AF, Ture U, AI- Mefty 0, Yasargil DCH. Microsurgery

of insular gliomas. Part 1: Surgical anatomy of the sylvian cistern. Contemp.

Neurosurgery 2002; 24 (11 ); 1-8.

74

7. Ture U, Yasargil MG, AI-Mefty 0, Yasargil DC.;Arteries of the insula.

J Neurosurg. 2000 Apr;92(4):676-87.

8. Yasargil MG, Caglar YS; in comments; on Varnavas GG, Grand W; The

insular cortex: morphological and vascular anatomic characteristics.

Neurosurgery. 1999 Jan; 44(1): 136-8.

9. Yasargil MG (ed): Microneurosurgery. Stuttgart: Thieme, Vol IVA, 1994,

p.43-56.

10. Yasargil MG (ed): Microneurosurgery. Stuttgart: Thieme, VoiiVB, 1996,

p.137-148.

11. lsnard J, Guenot M, Ostrowsky K, et al.. The role of the insular cortex in

temporal lobe epilepsy. Ann Neurol 2000;48: 614-23.

12. lsnard J, Guenot M, Sindou M, Mauguiere F. Clinical manifestations of

insular lobe seizures: a stereo-electroencephalographic study. Epilepsia. 2004

Sep;45(9):1 079-90.

13. Heffez DS. Stereotactic transsylvian, transinsular approach for deep­

seated lesions. Surg Neurol1997; 48:113-124.

75

14. Schatz R, Kreth FW, Faist M, Warnke PC, Volk B Ostertag B. Interstitial

125-lodine radiosurgery of low-grade gliomas of the insula of Rei I. Acta

Neurochir (Wein) 1994; 130: p.80-89.

15. Shankar A, Rajashekar V. Radiological and clinical outcome following

stereotactic biopsy and radiotherapy for low-grade insular astrocytomas.

Neurology India 2003; 51 (3); p.503-6.

16. Yasargil MG, von Ammon K, Cavazos E, et al. Tumours of the limbic and

paralimbic systems. Acta Neurochir (Wien) 1992; 118:40-52.

17. Duffau H, Capelle L, Lopes M, et al. The insular lobe: physiopathological

and surgical considerations. Neurosurgery 2000;47:801-811.

18. Lang FF, Olansen NE, DeMonte F, Gokaslan ZL, Holland EC, Kalhorn C,

Sawaya R. Surgical resection of intrinsic insular tumors: complication

avoidance.J Neurosurg. 2001 Oct;95(4):638-50.

19. Yasargil MG, Krisht AF, Ture U, AI- Mefty 0, Yasargil DCH. Microsurgery

of insular gliomas. Part II: Opening of the sylvian fissure. Contemp.

Neurosurgery 2002; 24 (12); 1-6.

76

20. Yasargil MG, Krisht AF, Ture U, AI- Mefty 0, Yasargil DCH. Microsurgery

of insular gliomas. Part Ill: pathophysiology and clinical presentation.

Contemp. Neurosurgery 2002; 24 (13); 1-6.

21. Yasargil MG, Krisht AF, Ture U, AI- Mefty 0, Yasargil DCH. Microsurgery

of insular gliomas. Part IV: Surgical treatment and outcome. Contemp.

Neurosurgery 2002; 24 (14); 1-8.

22. Hentschel SJ, Lang F. Surgical resection of intrinsic insular tumors.

Neurosurgery 57 [ONS Suppl 1 ]: ONS 176-0NS 183, 2005.

23. Vanaclocha V, Saiz-Sapena N, Garcia-Casasola C. Surgical treatment of

insular gliomas. Acta Neurochir (Wien) (1997) 139: 1126-1135.

24. Kleihues P, Berger PC, Scheithauer BW (eds): Histological Typing of

Tumours of the Central Nervous System, ed 3. Berlin: Springer-Verlag, 2000

25. Hall WA. Extending survival in gliomas: surgical resection or

immunotherapy? Surg Neurol2004; 61:145-8.

26. Ozyurt E, Kaya AH, Tanriverdi T, Tuzgen S, Oguzoglu SA, Hanefioglu et

al. New Classification for insular tumors and surgical results of 40 patients.

Neurosurgery Quarterly 2003; 13 (2): p.138-148.

77

27. Shapiro WR. Clinical features: Neurology of brain tumor and

paraneoplastic disorders. Chapter 42. in Youmans Neurological surgery V Ed.

2004. Ed. Winn HR. Saunders.

28. Hall WA. Extending survival in gliomas: surgical resection or

immunotherapy? Surg Neurol2004; 61:145-8.