Third ventricle

Anatomy and surgical classification of the 3rd ventricle and approaches to each part in illustrated pictures

1. Third Ventricle Mohamed Elsayed Elsebaey Neurosurgery Registrar Egypt, Ismailia Ministry of Health [email protected] Mohamed E Elsebaey

2. Fornix consists of 4 parts 1 ) Fimbria: Fimbria hippocampi over the dentate gyrus of hippocampus. The fimbria arises in the floor of the temporal horn on the ventricular surface of the hippocampal formation 2) Crus: 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 where it becomes related to trigon of lateral ventricle The two crura are connected to each other by the hipocampal commissure At the junction of the atrium and the body of the lateral ventricle, the paired crura meet to form the body of the fornix 3) Body: Formed by union of the two crura below the splenium of C.C. body. Then 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. 4) column: They arch along the superior and anterior margins of the foramena of Monro in their course toward the mamillary bodies.

3. Post Pre

4. Recesses of 3 rd ventricle are: 1) chiasmatic recess, 2) infundipular , 3) suprapineal , 4) pineal

5. The third ventricle is a narrow, funnel-shaped, unilocular , midline cavity . It has a roof, a floor, and an anterior, posterior, and two lateral walls.

6. Its boundaries: Roof : Tela choroida Floor : optic chiasma → infundipulum → tuber cinerium → mamiilary bodies → posterior perforated substance → tegmentum Anterior wall : superiorly by anterior commissure and cloumn of fornix and inferiorly by lamina terminalis Posterior wall : Pineal body → posterior comissure → superior colliculs → inferior colliculus Lateral wall : superiorly thalamus and inferiorly hypothalamus and in between is the hypothalamic sulcus

7. Surgical Anatomy Communicates with the lateral ventricle via the foramen of monro Drains posteriorly into the aqueduct of sylvius About one 1/3 of the 3 rd ventricle is located anterior to the foramen of monro Extends to optic chiasm inferiorly

8. Third Ventricle

9. Walls Anterior wall Consists mainly of the lamina terminalis Lamina terminals is thin sheet of pia and gray matter that runs from optic chiasm to the rostrum of the corpus callosum The columns of the fornix are found on the superior lateral margins The anterior commissure crosses the anterior wall at its upper end

10. Optic chiasm Hypothalamus Mamillary body Tegmentum Peduncle

11. When viewed from inferiorly, the structures forming the floor include, from anterior to posterior, 1) the optic chiasm (anterior 3 rd ventricle): The optic chiasm is located at the junction of the floor and the anterior wall of the third ventricle. The chiasm slopes posteriorly and superiorly from its junction with the optic nerves. The inferior surface of the chiasm forms the anterior part of the floor, and the superior surface forms the lower part of the anterior wall. The optic tracts arise from the posterolateral margin of the chiasm and course obliquely away from the floor toward the lateral margin of the midbrain. 2) the infundibulum of the hypothalamus, the tuber cinereum , (anterior 3 rd ventricle) 3) the mamillary bodies , (Line of demarcation between anterior and posterior 3 rd ventricle) 4) the posterior perforated substance , (posterior3 rd ventricle) 5) the part of the tegmentum of the midbrain located above the medial aspect of the cerebral peduncles. ( posterioir 3 rd ventricle)

12. Lateral Wall Is formed inferiorly by the hypothalamus ------------- superiorly by the thalamus ------------ posteriorly by the thalamus Massa Intermedia : Thalamic projection, that bridges the 3 rd ventricle at the superior posterior end

13. Floor Starts at the optic chiasm (anterior pole) Dips into the infundibular recess Jumping superiorly and posteriorly over (tuber cinereum , 2 mamillary bodies, posterior perforated substance) Floor of 3 rd Ventricle Cerebral peduncle Aqueduct of sylvius Anterior Posterior

14. Floor

15. Floor, when viewed from inside endoscopically

16. Column of fornix Anterior commissure Lamina terminalis

17. Roof Starts anteriorly at the foramen of monro End posteriorly at the supra pineal recess Is separated from the lateral wall by the choroidal fissure Choroidal fissure runs in the cleft between the upper part of the thalamus and fornix

18. The Roof has four layers : Fornix superior tela choroidea Velum Interpositum Inferior tela choroidea

19. Over ant. 1/3 of roof; Fornices run in parallel & attached to body of fornix Over Post. 1/3 of roof; The fornices are separated into forniceal crura The roof is covered entirly by layer or white matter called, hippocampal commissure Also Fornices & hippocampal commissure are covered by loose trabecular pial tissue in the form of two layers, called Tela Choroida

20. Between these 2 layers of tela choroida , is a space (Velum Interpositium ) through which Internal cerebral veins & Medial Posterior choroidal arteries , course.

21. Tela Choroidea Pia matter Sup . Att. to fornix Inf. Att. to thalamus Velum Interposium : Space Contains: Vessels: As & Vs Choroid plexus CSF

22. Tela choroidea : The tela choroidea consists of two thin, semiopaque membranes derived from the pia mater. The superior layer of the tela choroidea is attached to the fornix. The inferior layer of the tela choroidea is attached to the teniae thalami and the pineal body. Velum Interpositum : The velum interpositum is the space between the two layers of tela choroidea in the roof of the third ventricle. The two layers of tela chooridea are interconnected by loosely organized trabeculae and runs in between these two layers blood vessels (2 internal cerebral veins & 2 medial posterior choroidal arteries & paired parallel strands of choroid plexus ). The velum interpositum is usually a closed space that tapers to a narrow apex just behind the foramen of Monro, but it may infrequently have an opening situated between the splenium and pineal body that communicates with the quadrigeminal cistern to form the cisterna velum interpositum .

23. Internal Cerebral Vein (ICV) Starts at the posterior edge of the foramen of monro, and run posteriorly to exit the velum interpositium just above the pineal body.

24. 3 rd Ventricular choroid plexus: Attached to the roof by tela choroida Communicates through the choroidal fissure with the lateral ventriclar tela choroidea

25. Posterior Wall Begins at the sylvius aqueduct anteriorly & inferiorly , taking posterior superior direction Contains the posterior commissure, pineal body, habenular commissure & suprapineal recess above

26. Corpus callosum Above view

27. Opening the corpus callosum (CC)

28. Transcortical transventricular approach To The Anterior part of 3 rd Ventricle

29. Transcortical transventricular approach To Anterior part of 3 rd ventricle

30. Transcallosal paraforniceal approach

31. Intercallosal Interforniceal approach

32. 3 rd ventricle, viewed through open window in-between the columns of fornixes Anterior Posterior

33. Interhemispheric transcallosal Transchoroidal To Medium & Posterior Parts of 3 rd Ventricle

34. Frontal Trans-Lamina Terminalis Approach To 3 rd Ventricle

35. Infratentorial supracerebellar approach To The 3 rd Ventricle

36. Nose 3 rd ventricle Very similar to each other in the outline shape

37. Thanks