TECHNICAL NOTE

Awake stereotactic brainstem biopsy via a contralateral, transfrontal,transventricular approach

E. A. C. PEREIRA, T. JEGAN, A. L. GREEN & T. Z. AZIZ

Oxford Functional Neurosurgery, Department of Neurological Surgery, John Radcliffe Hospital, Oxford, UK

AbstractThe authors describe a novel approach to stereotactic biopsy of lesions of the lateral pons and medial cerebellar peduncle,and its diagnostic success without morbidity. A contralateral approach laterally expands the accessible infratentorial area. Itmay also confer a theoretical reduction in neurological deficit with passage through non-dominant right hemisphere.

Key words: Brainstem tumour, contralateral transventricular approach, stereotactic biopsy.

Clinical details

A 70-year-old right-handed man collapsed at home,

losing consciousness for 10 min. History revealed 2

months of right-sided weakness. Examination of the

oriented patient demonstrated bilateral horizontal

nystagmus, left lower facial nerve paresis, right-sided

hemiparesis (power 4/5), pronator drift, brisk reflexes

and an upward right plantar. Dysphagia to solids,

and subsequent aspiration pneumonia, were mana-

ged by intravenous antibiotics and nasogastric feed-

ing. Dexamethasone was not commenced as the

patient remained orientated and a diagnosis of

lymphoma had not been excluded. Magnetic reso-

nance imaging (MRI) showed extensive diffuse T2

high signal in the left pons, cerebral and middle

cerebellar peduncles, and some medullary extension

and fourth ventricle distortion without hydrocepha-

lus and minimal gadolinium enhancement (Fig. 1).

Single-voxel proton magnetic resonance spectro-

scopy (MRS) indicated markedly elevated choline

and decreased N-acetyl aspartate levels. A provi-

sional radiological diagnosis of diffuse low-grade

astrocytoma was made.

Informed patient consent was obtained to biopsy

the lesion and gain diagnostic histology. Stereotactic

surgery was planned using a Cosman–Roberts–Wells

base ring, 1-mm slice stereotactic CT and Radionics

Stereoplan1 software (Fig. 2). A contralateral arc

was chosen and collar setting enabling entry at

the coronal suture. A 2.7-mm twistdrill craniostomy

was performed after subgaleal bupivicaine with

epinephrine infiltration and stab incision. With the

patient awake throughout the procedure, a 2-mm

diameter Radionics Nashold1 biopsy needle with 10-

mm side window was slowly passed to target. The

patient was conversant throughout 1 h with the base-

ring attached and 20 min procedure duration,

reporting no pain, or alteration in visual or facial

function. A single cannula pass was conducted and

three significant tissue samples obtained by aspira-

tion from each of four quadrants. After slow biopsy

needle withdrawal without subjective deficits, the

scalp was closed by single layer suture. Urgent frozen

section and subsequent histology confirmed diffuse

low-grade astrocytoma. The patient complained of

horizontal diplopia in the first few postoperative

hours; this resolved with commencement of dexa-

methasone and he remained mobile with improve-

ment of his pneumonia during the first postoperative

week. Further oncological management was arranged

including palliative radiotherapy (30 Gy in 10

fractions).

Discussion

Brainstem lesions comprise only 2% of all brain

tumours in adults with very variable pathology, in

contrast to children where they account for up to

15% of brain tumours with diagnoses often made by

MRI alone. In adults, preoperative radiological

diagnosis is incorrect in one in five cases and

histology desirable, frequently changing both man-

agement and prognosis. In general, the majority of

Correspondence: Dr E. A. C. Pereira, Oxford Functional Neurosurgery, Department of Neurological Surgery, West Wing, John Radcliffe Hospital, Oxford,

OX3 9DU, UK. Tel: þ44 (0) 1865 741166. Fax: þ44 (0) 1865 231885. E-mail: eacp@eacp.co.uk

Received for publication 3 April 2008. Accepted 21 May 2008.

British Journal of Neurosurgery, August 2008; 22(4): 599 – 601

ISSN 0268-8697 print/ISSN 1360-046X online ª The Neurosurgical Foundation

DOI: 10.1080/02688690802220387

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adult brainstem tumours are not amenable to

surgical resection, making stereotactic biopsy an

attractive procedure for obtaining pathological tissue.

Stereotactic biopsy of brainstem lesions has been

performed for four decades with high diagnostic and

low complication rates. Its utility has been demon-

strated in non-enhancing diffuse astrocytomas as half

of those presumed to be low grade on MRI have been

high grade at biopsy.1 Proton MRS can be technically

limited at the skull base due to artefact from adjacent

tissues. Our experience of awake brainstem biopsies

is without operative mortality and with transient

neurological sequelae in 10% of patients, all of which

resolved either on cannula movement or within a few

hours of surgery.2 Our rationale is that biopsy-related

morbidity is reduced by keeping the patient awake

during the procedure, monitoring them clinically for

subjective reports of altered perception and assessing

them for weakness. Furthermore, reports of facial

paraesthesia, diplopia or oscillopia confirm anatomi-

cal localization. However, we have not had cause to

stop surgery due to intraoperative morbidity detected

by subjective reports from the awake patient.

The stereotactic approach to brainstem lesions is

traditionally ipsilateral and either transfrontal trans-

cortical, suboccipital transcerebellar or transtent-

orial. The transtentorial approach is now hardly

used, as its path crosses vital vasculature and cranial

nerves, and may cause pain with effortful tentorial

puncture. The suboccipital route can cause patient

discomfort with dissection of overlying musculature,

and requires patient positioning that makes intuba-

tion and general anaesthesia often necessary. The

transfrontal approach with the patient reclined or

supine is therefore favoured for awake surgery;

however, the ipsilateral route becomes limited to

midline regions of pons and medulla by the tentorial

incisura. A contralateral, transfrontal, extraventricu-

lar approach to the lateral pons enabling a wider

infratentorial pathological area to be sampled without

tentorial limitation or puncture has been described in

six patients without morbidity or mortality.3

We have not experienced the theoretically in-

creased risks of haemorrhage and target shift in

traversing a lateral ventricle that are thought to justify

a solely extraventricular intraparenchymal approach

over a transventricular one. In this case, the

transventricular trajectory was felt to give the best

chance of obtaining multiple biopsies in a single pass

with target shift unlikely in the confined infratentorial

space around the pons A contralateral transventri-

cular route does not increase distance from cranial

insertion point to target unlike an extraventricular

route, although no significant correlation has been

described between needle tract length and morbidity.

In this case, a contralateral approach might theore-

tically also have reduced biopsy-related morbidity by

passage through the non-dominant right hemisphere,

FIG. 1. (A) Axial T2-MRI. (B) Gadolinium-enhanced coronal T1-MRI showing a diffuse left pontine space occupying lesion.

600 E. A. C. Pereira et al.

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although we would not limit the procedure to left

infratentorial lesions.

Declaration of interest: The authors report no

conflicts of interest. The authors alone are respon-

sible for the content and writing of the paper.

References

1 Samadani U, Stein S, Moonis G, Sonnad SS, Bonura P,

Judy KD. Stereotactic biopsy of brain stem masses: decision

analysis and literature review. Surg Neurol 2006;66:484–90;

discussion 491.

2 Shad A, Green A, Bojanic S, Aziz T. Awake stereotactic biopsy

of brain stem lesions: technique and results. Acta Neurochir

(Wien) 2005;147:47–9; discussion 49–50.

3 Amundson EW, McGirt MJ, Olivi A. A contralateral, trans-

frontal, extraventricular approach to stereotactic brain-

stem biopsy procedures. Technical note. J Neurosurg

2005;102: 565–70.

FIG. 2. Contralateral, transfrontal, transventricular trajectory to the lateral pons.

Contralateral transventricular awake brainstem biopsy 601

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