Third ventricle

Connected laterally to lateral ventricles by means of Foramen of Monro and caudally to 4th ventricle by means of Aqueduct of sylvius

1. SURGICAL ANATOMY OF THIRD VENTRICLE DR PARTHA SARATHI MONDAL SENIOR RESIDENT NEUROSURGERY

2. CONCERNS IT IS LOCATED AT THE CORE OF THE CRANIUM AND DIFFICULT TO ACCESS. IT IS SURROUNDED BY CRITICAL NEURAL ELEMENTS. LESIONS OF THIRD VENTRICLE ARE NOT UNCOMMON

3. VENTRICULAR SYSTEM

4. GROSS ANATOMY Funnel shaped unilocular narrow midline cavity. Connected laterally to lateral ventricles by means of Foramen of Monro and caudally to 4 th ventricle by means of Aqueduct of sylvius . Possesses a roof, a floor, anterior wall, posterior wall and two lateral walls.

5. RELATIONS Anterior wall - Foramen of Monro -Anterior Commissure -Lamina Terminalis -Optic chiasma Posterior wall - Suprapineal rescess (4) - Habenular commissure -Pineal recess(5) & gland -Posterior commissure -Aqueduct of sylvius

6. RELATIONS-cont Floor - Optic Chiasma & recess - Infundibulum & recess -Pituitary gland -Tuber cinereum - Mamillary bodies -Posterior perforated subs Tegmentum of midbrain Roof -Body of fornix - Tella choroidea - Crura of fornix - Hippocampal commissure

7. LATERAL WALLS Stria medullaris thalami Medial surface of thalamus and hypothalamus with hypothalamic sulcus in between. Interthalamic adhesions(seen in 75%)

8. MICROSURGICAL ANATOMY

9. ROOF -Extending from foramen of Monro anteriorly to suprapineal recess posteriorly . -Consists of four layers: fornix, outer tela ch , vascular layer, inner tela ch from out to inward - Tela ch - thin translucent membranes derived from pia - Vascular layer enclosed in a space called velum interpositum in between two layers of tela . It contains posterior choroidal artery with its branches and internal cerebral veins with its tributaries.

10. Left lateral ventricle -Viewed from above after removal of upper frontal lobe exposing Foramen of Monro and adjoining parts of Rt lateral and 3 rd ventricle.Dissection done through Tenia fornicis

11. Floor Extends from optic chiasm anteriorly to aqueduct posteriorly . Anterior half-formed by diencephalic structures, anterior to posterior , optic chiasm, infundibulum of the hypothalamus, tuber cinereum , mamillary bodies posterior perforated substance. Tuber cinereum forms an internal elevation called median eminence whereas mamillary bodies form paired elevations just posterior to infundibular recess. Posterior half is formed by part of the tegmentum of the midbrain

12. Floor

13. Anterior wall Extends from Foramen of Monro above to optic chiasma below. Upper 1/3 rd hidden behind rostrum of corpus callosum and externally exposed lower 2/3 rd is formed by lamina terminalis and optic chiasm. Lamina terminalis is a thin sheet of grey and pia mater filling the gap(approx 10mm) between optic chiasma and anterior commissure . From anterosuperior to posteroinferiorly , floor is formed by , columns of fornix, foramen of Monro , anterior commissure , lamina terminalis , optic recess and chiasm.

14. Saggital section through 3 rd ventricle showing right lateral wall and anterior wall from left side.

15. Posterior wall Posterior wall extends from suprapineal recess above and aqueduct of sylvius below. From above downward it consists of suprapineal recess, habenular commissure , pineal body & its recess, posterior commissure &aqueduct of sylvius .

16. Pineal gland is projected to quadrigeminal cistern from a stalk with a recess inside enclosed by upper and lower lamina. Upper and lower laminiae crossed by habenular and posterior commissure respectively. At lower most part ,aqueduct connects the 3 rd ventricle with 4 th ventricle Internal structures of posterior wall seen from above

17. Common lesions of 3 rd Ventricle Congenital lesions Acquired lesions Aqueductal Stenosis Anterior mass- Seller- supraseller mass Chiasmatic -hypothalamic mass Cavum Veli Interpositi Cyst Posterior mass-pineal sol, tectal sol, Inferior thalamic sol Congenital Intraventricular Cysts Inferior mass- Hypothalamic hamartoma , Arachnoid cyst Mass near Foramen of Monro - Colloid cyst , SEGA, Subependymoma Intraventricular SOL- Choroid plexus neoplasm(Primary or Secondary), Congenital intraventricular cyst, Vascular malformation of choroid plexus

18. SURGICAL APPROACHES

19. Anterior transcallosal approach Basically a transcallosal-transventricular approach. Indications- Anterosuperior lesion or lateral ventricular extension. Advantages-access to both lateral ventricles as well, less neural incision, possible in nondilated ventricles. Corridor to entry into 3 rd ventricle- Transforaminal , transforniceal , transchoroidal . Nearby critical structures susceptible to injury- 1) Genu of internal capsule(in transforaminal )- Hemiplegia 2)Fornix-memory disturbance 3) Thalamostriate vein-drowsiness, hemiplegia , mutism. 4) Dorsomedial Nucleus of Thalamus-emotional disturbance

20. Caudate nucleus Tenia choroidea Internal cerebral vein Thalamus

21. Other Approaches to 3 rd ventricle Approaches Suitable for Advantage Disadvantage Collateral damage Anterior transcortical Predominantly lateral ventricular tumor with 3 rd ventricluar extension Easy access to c/l ventricle through septum pellucidum if required Mandatory cortical (MFG)incision. Difficult in nondialted ventricles. Risk of speech deficit in case of dominant hemisphere. Anterior subfrontal Anteroinferior lesion No cortical incision. Requires more brain retraction, working around vessels. Perforator vessel injury(ACOM in particular) Posterior transcortical (through sup parietal lobule) Posterior 3 rd ventricle and roof Good access to quadrigeminal cistern and also to pineal gland. Less spacious exposure, Needs cortical incision. Optic radiation,visuospatial defect, aphasia.

22. Approaches Suitable for Advantage Disadvantage Collateral damage Posterior transcallosal Posterosuperior 3 rd ventricular sol Working around great veins, higher chance of memory disturbance Injury to tectal plate, cerebellar arteries, trochlear nerve. Occipital transtentorial Pineal tumors with no C/L or posterior fossa extension No cortical incision. Deep venous system hinders easy access. Injury to tectal plate, cerebellar arteries, trochlear nerve, lateral & medial posterior choroidal artery Infratentorial supracerebellar Pineal tumors with posterior fossa extension Deep venous system doesn’t hinder easy access. More chance of injury to tectal plate tectal plate

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