Tentorial meningiomas

The detailed anatomy of the venous circulation and the tentorial incisura and classification of the tentorial meningiomas

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

2. Meningiomas of the posterior cranial fossa is about 9% of all intracranial meningiomas Tentorial meningiomas is about 30% of the posterior fossa meningiomas First described by Andral in 1833 Reviewing the deep venous system and venous drainage of the temporal lobe is the cardinal step when planning for the subtemporal and petrosal approach.

3. Tentorium Surgical Anatomy Tentorial cerebelli is dural duplication that covers the upper surface of the cerebellum and supports the occipital lobes Separating the supra from infra tentorial compartments

4. Borders Posterior attaches to the transverse ridges on inner surface of occipital bone. Enclosing the transverse sinuses Anterolateral Attaches to the superior ridge of the petrous portion of the temporal bone Enclosing the superior petrous sinuses on both sides Anterior Attached to the anterior and posterior clinoid processes Medial Medial free concave border that forms the tentorial incisura and bounding the midbrain.

5. Falx cerebelli Small triangular dural process Arises in midline from underneath the tentorium in-between the cerebellar hemispheres Upper surface connects to the posterior end of falx cerebri in midline Enclosing the straight sinus along the line of this junction

6. The straight sinus receives Vein of Galen & Inferior sagittal sinus ISS at the Tentorial apex and runs posteriorly to meet the transverse sinuses from both sides And the SSS from above at the torcular Herophili.

7. Incisural space is divided into Anterior In front of brain stem Middle Lateral to brain stem Posterior Behind brain stem

8. Tentorium Incisura

9. Arachanoid dissection to get the lateral walls of the chiasmatic , crural , ambient and interpeduncular cisterns is crucial step in surgery.

10. Neurovascular structures Anterior Incisural space: 3 rd cranial nerve Basal vein Posterior communicating artery Anterior choroidal artery Posterior cerebral artery (P1 & P2) Superior cerebellar artery

11. Neurovascular structures Middle tentorial incisura Cerebral peduncle & Upper pons medially Crural cistern : between uncus and cerebral peduncle anteriorly Ambient cistern : between midbrain and parahippocampal gyrus posteriorly 4 th cranial nerve Anterior choroidal artery Posterior cerebral artery P2 Superior cerebeller artery Basilar vein

12. 4 th cranial nerve: tiny nerve that exits from below the inferior colliculi and curves around the dorsal midbrain and enters the ambient cistern in the middle incisural space, supposed to be injured in subtemporal and petrosal approaches. Ambient cistern continues posteriorly into the quadrigeminal cistern.

13. Neurovascular structures Posterior incisural space quadrigeminal cistern is the main cistern This space forms the pineal region Related to the falcitentorial meningiomas Posterior cerebral artery Superior cerebellar arteries Vein of Galen

14. Blood supply ICA  intracavernous segment C4  meningiohypophyseal trunk  basal tentorial artery ( A. of Bernasconi – Cassinari ) S uperior cerebe ll ar artery P osterior cerebral artery

15. There are intradural venous sinuses inside the tentorium, that become more prominent when the major venous channels are blocked by the tumor. Those sinuses are source of brisk massive bleeding during dissection especially while using the occipital transtentorial approach. Bipolar coagulation can control this bleeding. No neurological deficit happens while occlusion of those intradural sinuses

16. Yasargil Classification T: Incisural Anterior ( T1 ) Middle ( T2 ) Posterior ( T3 ) T4 : Intermediate tentorial surface T5 : Torcular herophili T6 : Lateral outer tentorial ring anteriorly T7 : Lateral outer tentorial ring posteriorly T8 : Falcotentorial

17. Yasargil Classification T1 T2 T3 T4 T5 T6 T7 T8

18. Classification Supra tent. ------------- Infra tent.

19. Approaches

20. Supracerebellar infra tentorial Occipital trans tentorial

21. Subtemporal Approach

22. Area that must be known before dealing with the T1, T2, T3

23. Thanks