4 th ventricle- Anatomical and surgical perspective

4th ventricle connects the entire ventricular system of brain. Its connection with cisterns magna and cerebella pontine cistern via foramen of magenta and Luschka. CSF absorbs into the arachnoid granulation.

1. SURESH BISHOKARMA, MS MCH RESIDENT, NEUROSURGERY NINAS FOURTH VENTRICLE ANATOMY AND SURGICAL PERSPECTIVE

2. The fourth ventricle is a broad, tent- shaped midline cavity located between cerebellum and brainstem. It is lined by a membrane consisting of ependyma and a double fold of pia mater which constitutes the  tela choroidea of the fourth ventricle .

3. COMMUNICATION

4. It has a roof, a floor and two lateral recesses

5. The roof : superior and inferior medullary velum and cerebellar vermis . Apex: tented into cerebellum The   upper part  of the roof :superior cerebellar peduncles and the superior medullary velum (thin sheet of white matter). The   inferior part  of the roof : I nferior medullary velum (non-nervous tissue): Medulloblastoma origin.( Youman ) ROOF

6. FLOOR OF FOURTH VENTRICLE Each inferolateral margin of the floor is marked by a narrow white ridge called taenia . The right and left taeniae meet at the inferior apex of the floor to form a small fold called the obex .

7. The lateral recesses : pouches : below the cerebellar peduncles: Luschka CPA. The ventral wall of each lateral recess is formed by the junctional part of the floor and the rhomboid lip. The rostral wall of each lateral recess : Caudal margin of the cerebellar peduncles. The peduncle of the flocculus , which interconnects the inferior medullary velum and the flocculus , crosses in the dorsal margin of the lateral recess. LATERAL RECESS

8. LATERAL RECESS

9. The caudal wall is formed by the tela choroidea , which stretches from the taenia and attaches to the edge of the peduncle of the flocculus . The rootlets of the glossopharyngeal and vagus nerves arise ventral, and the facial nerve rostral, to the choroid plexus, which extends through the lateral recess and the foramen of Luschka into the CPA. The fibers of the vestibulocochlear nerve cross the floor of the recess. LATERAL RECESS

10. LATERAL RECESS

11. T he cavity or fossa of the fourth ventricle communicates with the third ventricle superiorly as a continuation of the cerebral aqueduct. Inferiorly it extends as the central canal of the brainstem , which in turn runs through the vertebral column. The cavity also communicates with the subarachnoid space through the three apertures. CAVITY

12. F oramina of the fourth ventricle

13. F irst described during the 19th century. Franc ̧ois Magendie :French physiologist Magendie ( 1783-1855): Pioneer of experimental physiology. Hubert von Luschka : German anatomist ( 1820-1875 ). Rhoton provided detailed descriptions of the neurosurgical anatomy of the fourth ventricle and its foramina. FORAMINA OF 4 TH VENTRICLE

14. The choroid plexus of the fourth ventricle consists of several segments . Its lateral segments extend laterally through the foramina of Luschka (protruding into the cerebellopontine angle below the flocculus and behind the glossopharyngeal, vagus and accessory nerves) and Its medial segments extend longitudinally through the foramen of Magendie . The tonsillar parts of the choroid plexus are located anterior to the tonsils and extend inferiorly through the foramen of Magendie . CHOROID PLEXUS OF 4 TH VENTRICLE

15. The PICA is intimately related to the inferior half of the roof. The PICA segment coursing in the cleft between the tonsil on one side and the tela and velum on the opposite side is referred to as the “ telovelotonsillar segment ”3. This PICA loop, which forms a convex rostral curve in its course around the rostral pole of the tonsil, is also referred to as either the “cranial” or “ supratonsillar loop.” VASCULAR RELATIONS

16. PICA

17. The apex of the cranial loop faces the inferior medullary velum. It is from this PICA segment that the choroidal branches to the tela and choroid plexus arise. The segment, which passes across the posterior medulla, often forms a caudally convex loop that coincides with the caudal pole of the tonsil, but it may also course superior or inferior to the caudal pole of the tonsil without forming a loop. Most PICAs bifurcate into a medial and a lateral trunk in their passage around the tonsil. The medial trunk ascends to supply the vermis and the adjacent portion of the hemisphere, and the lateral trunk passes laterally over the tonsil to supply most of the hemispheric and tonsillar surfaces.

18. The main trunks of the anterior inferior cerebellar artery course near the foramen of Luschka , where they extend small choroidal branches to the tela and choroid plexus in the lateral recess.

19. The largest vein of the cerebellomedullary fissure Originate: nodule and uvula, courses laterally near the junction of the inferior medullary velum and tela choroidea , Courses: dorsal or ventral to the flocculus CPA Superior petrosal sinus. Venous system

20. Ikezaki and co-workers , classified posterior fossa ependymomas into three groups based on location: (1)The lateral type presenting in the CPA characterized by a poor prognosis secondary to involvement of cranial nerves and brainstem; ( 2) E pendymomas localized to the floor of the fourth ventricle with an intermediate prognosis ; and ( 3) Those localized to the roof of the fourth ventricle with the most favorable outcome. Leptomeningeal dissemination Medulloblastoma : 33%. Ependymoma : 8 % to 12 %. Spread and dissemination route

21. Hydrocephalus  is one of the conditions that can result from blockage of the median and lateral apertures. In   Arnold Chiari malformation  (Type II Chiari malformation), the medulla and the tonsils of the cerebellum come to lie in the vertebral canal by descending through the foramen magnum. The median and lateral apertures are blocked by this condition leading to obstruction of CSF flow. This causes internal hydrocephalus . Chiari II can also present with syringomyelia due to the development of CSF-filled cyst or syrinx. CLINICAL IMPORTANCE OF 4 TH VENTRICLE

22. PICA

23. Medulloblastoma  is the most common malignant brain tumour in children, which arises in the cerebellum and can therefore impinge on the roof of the fourth ventricle. The area postrema  of the caudal region of the fourth ventricle is also of clinical significance because of its role in the control of  vomiting .

24. In adults, the occlusion is rather acquired than congenital, linked to infection, head trauma, intraventricular haemorrhage , tumours or Arnold- Chiari malformation. Despite its rare occurrence, congenital imperforation or membranous obstruction of the foramen of Magendie must be considered as a possible etiology of chronic hydrocephalus in adult.

25. Main pathological conditions affecting the foramina of the fourth ventricle 1 Occlusion (Infection, head trauma, intraventricular haemorrhage , space- occupying lesions, congenital anomalies) 2 Membrane obstruction 3 Congenital imperforation (agenesis) 4 Idiopathic stenosis 5 Arachnoid adhesions 6 Cystic dilation

26. Tumors of the ventricular system account for less than 1% of intracranial lesions, most of which are benign and slow growing. 14% of all ventricular tumor occurs within the fourth ventricle. Tumor originating in 4 th Ventricle Medulloblastoma : most common: childhood. Ependyoma : most common : adults Hemangioblastoma Epidermoid cyst Tumor expanding inside the 4 th Ventricle. Astrocytoma Oligodendroglioma Exophytic cavernous malformation Tumor of 4 th venticle

27. Medulloblastoma Usually originates from inferior medullary velum from germinative cells originating in the neuroepithelial roof of the fourth ventricle and grow anteriorly into the fourth ventricle .

28. Hemangioblastoma

29. CHOROID PLEXUS PAPILLOMA

30. APPROACH TO 4 th VENTICULAR TUMOR

31. • Midline pathology of the fourth ventricle that arises from the cerebellar vermis or brainstem •Tumors : Medulloblastoma , ependymoma-subependymoma , as- trocytoma , choroid plexus papilloma, hemangioblastoma , dermoid-epidermoid cysts, brainstem glioma , and metastatic lesions . • Vascular lesions: Arteriovenous and cavernous malformations • Inflammatory and infectious conditions: Cerebellar and brainstem abscesses • Traumatic or spontaneous hematomas INDICATION

32. CSF diversion : endoscopic ventriculostomy , external ventricular drain or permanent ventriculoperitoneal shunt. followed by microsurgical resection of the underlying ventricular tumor. Emergency: Acute obstructive hydrocephalus or intratumoral hemorrhage. INDICATIONS

33. In the past, operative access to the fourth ventricle was obtained by splitting the cerebellar vermis or by removing part of a cerebellar hemisphere.

34. Dandy: M edian suboccipital craniectomy and splitting the vermis TRANSVERMIAN APPROACH

35. T ransvermian approach provided slightly better visualization of the medial part of the superior half of the fourth ventricular roof. ( Disadv : Lateral recess) In cases where a tumor is located around the fastigium or originates from the vermis . ADVANTAGES

36. It avoids complications related to injuries of the posterior inferior cerebellar artery (PICA) branches to the brainstem and the inferior and middle cerebellar peduncles.

37. TELOVELAR ( TRANSCEREBELLO-MEDULLARY FISSURE) APPROACH 1980:Rhoton AL Jr This approach is identical to traditional midline approaches . P reserve the cerebellar tissue : Anatomic plane through the tela choroidea and velum interpositum .

38. O pening the CMF : safe retraction of the cerebellar hemisphere Good visualization of lateral recess. T he cerebellar mutism syndrome: Avoids vermian split Early vascular control. ADVANTAGES OF TELOVELAR APPROACH

39. STEPS OF TELOVELAR APPROACH

40. POSITIONING

41. INCISION

42. The craniotomy includes opening of the foramen magnum dorsally and is larger in the superior portion than in the inferior. CRANIOTOMY

43. Dural opening is usually performed in a Y-shaped fashion . Bleeding from the occipital sinus can be controlled with silver dural clips or bipolar coaguation or running silk suture DURAL OPENING

44. DECOMPRESSION OF CISTERNA MAGNA

45. Opening techniques for the telovelar approach depending on different targets Matsushima T et al.

46. Small arachnoid trabeculae around the tonsil is sharply cut and cerebellar tonsil is gently elevated off its inferior fixation. The superior portion of the tonsils is separated from the cerebellar vermis on both sides to gain access to the tela choroidea . Careful inspection of the tela reveals small branches of the PICA that supply the choroid plexus.

47. In similar fashion, the caudal loop of the PICA is freed from the neuraxis by incising small arachnoid trabeculae while slightly retracting the tonsils laterally

48. T he uvula of the cerebellar vermis is elevated gently with a self-retaining retractor, and the arachnoid between the uvula and the tonsil is gradually incised to expose the course of the PICA.

49. The telovelar junction is visualized T he superior medullary velum may be further divided to allow for more rostral exposure of the fourth ventricle.

50. When the roof of the fourth ventricle is adequately opened to allow for exposure of the tumor, the interface of the tumor and the brainstem is inspected. Cottonoid strip along floor and cervicomedullary junction

51. Superior and lateral edges : adherence to the cerebellum . Larger tumors: debulk the tumor : lateral margins. A point of origin of the tumor : more adherant part TUMOR INSPECTION

52. Hemostasis: cerebellum: bipolar cautery or tamponade Inspect aqueduct : blood clot. Saline irrigation until clear Finishing touch

53. Closure

54. Retraction injury to cerebellar tonsils, vermis , and cerebellar peduncles Injury or occlusion of posterior inferior cerebellar arteries from retraction. Injury to the floor of the fourth ventricle ( brainstem) T racking of blood into third and lateral ventricles that may produce hydrocephalus. Injury to the transverse sinus during the craniotomy. Significant blood loss or air emboli from occipital sinus or midline occipital bone . Tumor dissemination along foramina and obex Avoidances/Hazards / Risks

55. Postoperative hematoma CSF leak Infection Cranial nerve deficits or other brainstem deficits Hydrocephalus Cerebellar deficits Supratentorial epidural hematoma Tumor residual or recurrence Posterior inferior cerebellar artery or vertebral artery infarction Cerebellar edema Complications

56. M edulloblastoma ( 13), ependymoma ( 10), and then choroid plexus papilloma ( 2). GTR:8 cases (32%), near total ( ˃80% of tumor volume) in 14 cases (56%), and subtotal excision (˂80% of tumor volume) in 3 cases (12%). Cerebellar mutism in 2 cases (8 %), facial palsy: 2 cases(8%), postoperative bulbar affection: 3 cases (12 %) Mortality: 2 Conclusion : Telovelar approach: access : Low incidence of CM Retrospective study 25 cases with midline posterior fossa tumors 2012-2014 Neurosurgery Department, Cairo University, Egypt Refaat MI, Elrefaee EA, Elhalaby WE ( 2016 ) Telovelar Approach for Midline Posterior Fossa Tumors in Paediatrics : 25 Cases Experience. J Neurol Disord 4:315. doi : 10.4172/2329-6895.1000315

57. Thank you  Mussi AC ,  Rhoton AL. Telovelar approach to the fourth ventricle: microsurgical anatomy. JNS.  2000;92(5):812-23 . Schmidek and Sweet operative technique; 6 th Edn Refaat MI, Elrefaee EA, Elhalaby WE.Telovelar Approach for Midline Posterior Fossa Tumors in Paediatrics : 25 Cases Experience. J Neurol Disord . 2016 ; 4:315 References