Inter-hemispheric Approach

Sherif Elwatidy FRCS(SN), M.D.Professor of NeurosurgeryCollege of Medicine, KSU

Contents

• Anatomy• Scope of vision• Indications• Patient Positioning• Basics & Techniques

Exposure of the 3rd ventricle by IH approach

Two basic principles for safe exposure of the 3rd Ventricle1. Minimize trauma to neurovascular structures2. Maximum line of vision

This achieved by 3. Adequate preoperative imaging and planning 4. Proper placement of skin incision and bone flap5. Proper placement of callosotomy

Anatomy of the Lateral ventricle• Each lateral ventricle is a C-shaped

cavity that wraps around the thalamus.

• Each lateral ventricle has five parts: the frontal, temporal, and occipital horns, the body, and the atrium.

• Each of these five parts has medial and lateral walls, a roof, and a floor.

• These walls are formed by: thalamus, septum pellucidum, deep cerebral white matter, corpus callosum, and two C-shaped structures, the caudate nucleus and the fornix, that wrap around the thalamus.

Anatomy of the Lateral ventricleThalamus• The thalamus is located in the center of the

lateral ventricle. • Each lateral ventricle wraps around the

superior, posterior & inferior surfaces of the thalamus .

• The body of the lateral ventricle is above the thalamus,

• The atrium and occipital horn are posterior to the thalamus,

• The temporal horn is inferolateral to the thalamus.

• The superior surface of the thalamus forms the floor of the body

• The posterior surface of the pulvinar of the thalamus forms the anterior wall of the atrium,

• The inferior surface of the thalamus is situated at the medial edge of the roof of the temporal horn.

Anatomy of the Lateral ventricleCaudate Nucleus

• The caudate nucleus is an arched, C-shaped, cellular mass that wraps around the thalamus and constitutes an important part of the wall of the lateral ventricle

• It has a head, body, and tail.• The head bulges into the lateral wall of the frontal

horn and body of the lateral ventricle. • The body forms part of the lateral wall of the

atrium,• The tail extends from the atrium into the roof of the

temporal horn and is continuous with the amygdaloid nucleus near the anterior tip of the temporal horn.

• In the body of the lateral ventricle, the caudate nucleus is superolateral to the thalamus;

• In the atrium, it is posterolateral to the thalamus;• In the temporal horn, it is inferolateral to the

thalamus. • The stria terminalis, a fiber tract that runs parallel

and deep to the thalamostriate vein(lat part of the floor of th lateral vntricle), arises in the amygdaloid nucleus and courses along the border between the caudate nucleus and the thalamus in the wall of the ventricle from the temporal horn to the body.

Anatomy of the Lateral ventricleFornix• The fornix is another C-shaped structure that wraps

around the thalamus in the wall of the ventricle (Fig. 5.1A). The fornix consists mainly of hippocampomamillary tract fibers that originate from the hippocampus, subiculum, and dentate gyrus of the temporal lobe. The fimbria arises in the floor of the temporal horn on the ventricular surface of the hippocampal formation and passes posteriorly to become the crus of the fornix. The crus wraps around the posterior surface of the pulvinar of the thalamus and arches superomedially toward the lower surface of the splenium of the corpus callosum. At the junction of the atrium and the body of the lateral ventricle, the paired crura meet to form the body of the fornix, which runs forward along the superomedial border of the thalami in the medial wall of the body of the lateral ventricle. The body of the fornix separates the roof of the third ventricle from the floor of the bodies of the lateral ventricles. At the anterior margin of the thalamus, the body of the fornix separates into two columns that arch along the superior and anterior margins of the foramen of Monro in their course toward the mamillary bodies. In the area below the

IndicationsTumors1. Colloid cyst

IndicationsTumors1. Colloid cyst

IndicationsTumors2. 3rd ventricle tumors

IndicationsTumors2. 3rd ventricle tumors

IndicationsTumors3. Lateral ventricle tumors

IndicationsTumors4. Pineal tumors

IndicationsTumors5. Thalamic and caudate tumors

IndicationsTumors6. Falx meningioma

IndicationsTumors6. Falx meningioma

IndicationsVascular lesions 1. Pericallosal aneurysms

IndicationsVascular lesions 2. AVMs

Patient positioning• Supine position• Operating table slightly

flexed with head up• Three point head fixator• Head slightly flexed or

extended according to required line of vision

Scalp incision

Skin incision• Skin flap crossing the midline /

or bicoronal incision 2/3 anterior and 1/3 posterior to coronal suture

• Scalp flap should expose the Cr. And Sag. Sutures.

Bone flap• May be adjusted to avoid

major veins• Should fully expose SSS• Should not extend more

than 2 cm behind Cr. Suture• 2 or more BH depends on

adherence of dura to the bone

• Location of the burr holes (midline/ paramedian)

Heamostasis

• Bleeding SSS• Bleeding dura• Bleeding cortical vein & Bridging veins• Bleeding from brain tissue• Bleeding from deep venous system

(thalamostriate, internal cerbral,..Vs.)• Bleeding from major arteries (repair, stent,..)

Dural opening & Brain Retraction• Dura l flap based on the SS

sinus.• Preserve venous structures,

pacchionian granulations, and the pia mater.

• Use microscope for dural opening.

• Gentle dural retraction.• Gradual, gentle, stepwise

retraction of the medial surface of the hemisphere along the falx till inferior margin of the falx.

• Identify Calloso-marginal artery which is the guide to corpus callosum.

• Corpus callosum is pearly white in color as opposed to creamy tan color of cingulate gyrus.

• 1.5-2cm callosotomy using bipolar-suction technique, once ventricle is entered the retractor is advanced just past the callosal margin.

Orientation in Lateral ventricle

•Orientation is verified by the orientation of the choroid plexus and thalamostriate vein•If opposite ventricle is entered , further lateral resection of the corpus callosum / or penetration and resection of the septum pellucidum can be performed to provide entry into the opposite lateral ventricle

Entry into the 3rd ventricle

1. Foraminal entry through the foramen of Monro (is always prefered )

2. Inter-fornicial entry

3. Choroidal fissure