ANATOMY OF THIRD VENTRICLE ANDSURGICAL APPROACHES

DR PRAVEEN K TRIPATHI

HISTORICAL REVIEW HEROPHILUS(335-280 B.C):First to describe

ventricles GALEN(129-200A.D):Described ventricles in

detail,studied the symtoms and signs of hydrocehalus

LEONARDO DA VINCI(1452-1519):First wax casting of ventricles

WALTER DANDY(1886-1946):First pneumoencephalography

HISTORICAL REVIEW First successful endoscopic third ventriculostomy

(ETV) was performed in 1923 by william J. Mixter . In 1947, mcnickle described a modified technique of

performing a percutaneous third ventriculostomy utilizing a 19-gauge needle to puncture the floor of the third ventricle.

In 1952, Nulsen and Spitz first reported creation of a shunt diverting cerebrospinal fluid (csf) from the ventricular system to the jugular vein.

1990 Jones Etal reported successful ETV in 24 pt.

Third ventricle is a narrow slit-like cavity whose lateral walls are formed by the thalamus and hypothalamus on either side. At the rostral margin of the midbrain, the cerebral aqueduct opens into the third ventricle.

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Third Ventricle -ventriculus tertius

The third ventricle is a narrow, funnel-shaped, unilocular midline cavity.

Slit-like space, lying in the sagittal plane It communicates at its anterosuperior margin with

each lateral ventricle through the foramen of monro and posteriorly with the fourth ventricle through the aqueduct of sylvius.

Neural tube

Third Ventricle Comprises of:

Anterior wall

Two side walls

Floor

Roof

Third Ventricle Anterior wall:

lamina terminalis anterior commissure

Two side walls:

Thalamus Interthalamic adhesion (60% of brains)

Hypothalamus Supraoptic nucleus – ADH Paraventricular nucleus – Vasopressin/Oxytocin

Subthalamus Subthalamic nucleus

The lamina terminalis has been opened.The chiasmatic recess is located between the lower part of the lamina terminalis and the posterior part of the optic chiasm.

Anterior wall of the third ventricle

The anterior communicating artery commonly passes in front of the lamina terminalis. Perforating arteries arise from a precallosal branch of the anterior communicating artery and penetrate the anterior wall of the third ventricle to reach the columns of the fornix.

Anterior wall of the third ventricle

The roof The roof extends from the foramen of Monro

anteriorly to the suprapineal recess posteriorly

constituted superiorly to inferiorly by five layers

the fornix the superior membrane of the tela choroidea vascular layer located in a space between the

superior and inferior membranes of the tela choroidea called the velum interpositum

the inferior membrane of the tela choroidea the choroidal plexus of the third ventricle

Roof of the third ventricle through a transchoroidal approach.

1, Head of the caudate nucleus and anterior caudate vein;

2, rostrum of the corpus callosum;

3, column of the fornix;

4, anterior septal vein;

5, foramen of Monro;

6, body of the fornix;

7, thalamostriate vein;

8, inferior membrane of the tela choroidea and choroid plexus of the third ventricle (the superior membrane of the tela has been removed);

9, body of the caudate nucleus and thalamostriate vein;

10, dorsal surface of the thalamus;

11, internal cerebral vein and medial posterior choroidal artery;

12, splenium of the corpus callosum.

The roof of the ventricle is formed by pia-ependyma, which spans between the two striae medullaris thalami, situated along the dorsomedial border of the thalamus. 15

In the rostral part of the third ventricle lies an aperture, the interventricular foramen or foramen of Monro, which is located between the column of the fornix and the anterior pole of the thalamus.

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Cont..

The floorThe floor extends from the Anteriorly-optic chiasm Posteriorly- to the orifice of the aqueduct of

SylviusFrom anterior to posterior The optic and infundibular recesses, The tuber cinereum, The mamillary bodies, The posterior perforated substance, The midbrain, and the aqueduct

THIRD VENTRICLE

CHOROIDAL FISSURE AND CHOROID PLEXUS

The choroidal fissure is the narrow C shaped cleft between the fornix and the thalamus along which the choroid plexus is attached

The fissure extends from the foramen of Monro to the choroidal point along the surface of thalamus

Choroid plexus continues as two parallel strands of plexus in the roof of third ventricle

Cont..

Choroidal arteries arise from internal carotid and posterior cerebral arteries and enter the ventricles through the choroidal fissure

Choroid plexus is divided into body,atrial and temporal parts

LESIONS WITHIN THIRD VENTRICLE

Anterior third ventricle1. colloid cyst2. sellar mass3. sarcoidosis4. aneurysm5. hypothalamic glioma6. histiocytosis7. meningioma8. optic glioma

Posterior third ventricle1. pinealoma

(dysgerminoma)2. meningioma3. arachnoid cyst4. vein of Galen aneurysm

(A, foramen of Monro; B, anterior third ventricle;C, posterior third ventricle) and relevant vascular anatomy of the third ventricle.

Schematic representation highlighting common tumor locations

THIRD VENTICLE-APPROACHES

THIRD VENTRICLE -APPROACHES

THIRD VENTRICLE -APPROACHES

COMBINED TRANSLAMINAR TRANSCORTICAL

Indications Transventricular (Wegen’s)–Tumors arising

in corpus callosum and extending to third ventricle

Transcallosal (Dandy’s)–Tumor extending to splenium

Occipital‐transtentorial ( Popen’s) –Tumor extending to medial wall of ventricle and in occipital lobe

Supracerebellar infratentorial (krause’s) –Pineal region tumors

Approach to Ant. TV tumors

Subfrontal Frontotemporal Anterior transcallosal Anterior transcortical Transsphenoidal

Corridors Interoptic Opticocarotid Lamina terminalis Transfrontal‐transsphenoidal Lamina terminalis‐rostrum of callosum

approach

THIRD VENTRICLE -APPROACHES

Corridors For Transcallosal Approach

THIRD VENTRICLE -APPROACHES

Transcortical approach to the lateraland third ventricles.

A, the scalp incision (solid line) and bone flap (dotted line) are centered over the middle frontal gyrus.

B, The cortical opening exposes the right lateral ventricle.

C, the third ventricle has been exposed by opening the choroidal fissure along the site of the attachment of the choroid plexus to the fornix. This exposes the internal cerebral veins and medial posterior choroidal arteries in the roof of the third ventricle.

TRANSCORTICAL VS TRANSCALLOSAL PROS

TRANSCORTICAL VS TRANSCALLOSAL CONS

Subfrontal approach

Supine position with head extension Coronal flap incision Quadrangular craniotomy flush with orbital margins Frontal sinus exteriorized and packed Olfactory nerve divided if necessary

Frontotemporal or subtemporal approach

Frontotemporal craniotomy Dura reflected on sphenoid ridge Tumor approached through corridor between

third nerve and carotid. Temporal pole can be elevated or resected.

Anterior transcallosal approach

Advantages –Short trajectory to third ventricle –Can access posterior and basal TV –Bilateral exposure of foramina of monro –No requirement of ventriculomegaly

Maneuvers for TV entry

transforaminal Transchoroidal Transfornicial

Transforaminal

Gives access to anterior TV Foramen of monro identified Initial dilatation can be tried Incision is made through one column of

fornix at anteriosuperior edge.

Transchoroidal Entry into the middle of TV Opening through the velum interpositum Two approaches: Suprachoroidal •Incision in tinea forniciaSubchoroidal •Incision in teniea choroidea

Roof of the third ventricle through a transchoroidal approach.

1, Head of the caudate nucleus and anterior caudate vein;

2, rostrum of the corpus callosum;

3, column of the fornix;

4, anterior septal vein;

5, foramen of Monro;

6, body of the fornix;

7, thalamostriate vein;

8, inferior membrane of the tela choroidea and choroid plexus of the third ventricle (the superior membrane of the tela has been removed);

9, body of the caudate nucleus and thalamostriate vein;

10, dorsal surface of the thalamus;

11, internal cerebral vein and medial posterior choroidal artery;

12, splenium of the corpus callosum.

Transfornicial

Identify the septum pellucidum Develop a plane between septa. Incision is given in the body of fornix not

exceeding 2 cm behind the FM.

Complications Fornicial injury–Recent memory disturbances Vascular compromise–Basal ganglia infarcts Thalamic infarcts–Limbic system ischemia Hippocampal syndrome

Approaches to the post TV tumors

Transventricular Interhemispheric transcallosal Occipital transtentorial Infratentorial supracerebellar

Endoscopy

Treatement of choice for malignant third ventricular tumors

Biopsy of lesion Post operative radiotherapy Treatment of hydrocephalus

CHOICE OF ENDOSCOPIC ENTRY POINT

Indications -ETV

FAVOURABLE FACTORS-ETV

A, Oblique view showing the endoscope passing through the lateral ventricle and foramen of Monro and into the third ventricle. B, Sagittal view depicting the perforation of the floor of the third ventricle. It is important to understand the close relationship of the floor of the third ventricle to the anterior structures (optic chiasm, infundibulum, and clivus) and posterior structures (basilar artery and brainstem) to avoid undesired complications.

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Schematics demonstrating the surgical trajectory for ETV using a rigid endoscope

LOCATION OF ETVThe location of the opening is chosen:A. in the midlineB. in the region of the tuber cinereum

(prominence of the base of the hypothalamus, extending ventrally into the infundibulum and pituitary stalk)

C. posterior to the infundibular recessD. anterior to the mammillary bodiesE. anterior to the tip of the basilar artery

. A, View of foramen of Monro from right lateral ventricle. The choroid plexus (center), anterior septal vein (medial), and thalamostriate vein (lateral) are seen. Care must be taken not to damage these structures when entering the foramen of Monro in order to prevent hemorrhage or venous infarcts.

B, View of the floor of the third ventricle. From anterior to posterior, the optic chiasm, infundibulum, tuber cinereum, paired mammillary bodies are clearly seen. The basilar artery can also be seen between the mammillary arteries and must be avoided upon perforation of the third ventricular floor.

Intraoperative views and corresponding schematic representations

showing the thin area in front of the mamillary bodies (yellow arrow) through which a third ventriculostomy is completed.

FLOOR OF THIRD VENTRICLE

ETV

COMPLICATIONS

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