ANATOMY OF TENTORIUM INCISURA

anatomy of TENTORIUM INCISURA
tentorium cerebelli
neurosurgery
cerebellum
brain cisterns

1. Tentorial Incisura Dr. A.Supriya 2 nd year post graduate Dept of Neurosurgery AMC/KGH

2. Tentorium cerebelli   T entorium cerebelli  (Latin for "tent of the cerebellum") is an extension of the duramater  between the inferior aspect of the occipital lobes and the superior aspect of the cerebellum. 

3. Tentorium cerebelli   The anterior border is attached to the petrous ridge and divides to enclose the superior petrosal sinus. The lateral and posterior borders, which divide to enclose the transverse sinus and the torcula, are attached to the inner surface of the occipital and temporal bones along the internal occipital protuberance

4. Tentorium cerebelli  

5. Oculomotor trigone The anterior end of each free edge is attached to the petrous apex and the anterior and posterior clinoid processes The anterior and posterior petroclinoid the interclinoid fold. Between these folds is located the Oculomotor trigone Trochlear nerve enters the dura at the posterolateral edge of this triangle.

6. Tentorium cerebelli The dura forming the roof of the oculomotor trigones extends medially across the sella to form the diaphragma sellae, which covers the pituitary gland and contains an opening for the infundibulum.

7. Tentorium incisura The free border of the tentorium is U-shaped – Ogilivie shaped ; it forms an aperture – the Tentorium incisura - which gives passage to the midbrain The incisura is roughly triangular and has its anterior edge or base on the dorsum sellae and its apex dorsal to the midbrain, just posterior to the pineal gland The width of the incisura varies from 26 to 35 mm (average, 29.6 mm) and the anteroposterior diameter varies from 46 to 75 mm (average, 52.0 mm)

8. Tentorium incisura Ogilivie

9. Tentorium incisura

10. Tentorium incisura The description of Each incisural space will be described in sections on neural, cisternal, ventricular, cranial nerve, arterial, and venous relationships

11. The lateral and 3 rd ventricles are situated above tentorium incisura. Area b/w brain stem & free edges is divided in to Ant. incisural space-in front of brain stem Paired middle incisural spaces-lateral to brain stem Posterior incisural space-behind brain stem

12. Anterior incisural space

13. Anterior incisural space - Neural relations Extends obliquely Forward and Upwards Superiorly - the optic chiasm to the subcallosal area. Inferiorly - between the brainstem and clivus Laterally - into the medial part of the Sylvian fissure Posteriorly - The pons and cerebral peduncles to the middle incisural space.

14. Anterior incisural space

15. Anterior incisural space – Cisternal relations This Space mainly consists of interpeduncular cistern (b/w cerebral peduncles); part of Sylvian cistern; chiasmatic cistern (below optic chiasm); cisterna lamina terminalis (ant to lamina terminalis) Interpeduncular & chiasmatic cisterns are separated by Liliequist’s membrane (arachnoid sheet extending from dorsum sella to anterior edge of mammillary bodies)

16. Liliequist’s membrane Lillequist membrane is a projection formed by arachnoid membrane extending from dorsu sella to mammillary bodies just beneath the floor of 3 rd ventricle

17. Anterior incisural space – Cisternal relations The chiasmatic cistern communicates around the optic chiasm with the cisterna laminae terminalis, which lies anterior to the lamina terminalis

18. Anterior incisural space – Cisternal relations

19. Anterior incisural space Ventricular relations Frontal horns and Anterior part of 3 rd Ventricle projects into anterior incisural space

20. Anterior incisural space Cranial Nerves The optic nerves emerge from the optic canal medial to the attachment of the free edge to the anterior clinoid processes, and are directed posteriorly, superiorly, and medially toward the optic chiasm. Optic nerves & chiasm cross ant. Incisural space. From chiasm, optic tract continues around cerebral peduncle to enter middle incisural space

21. Anterior incisural space Cranial Nerves

22. Oculomotor trigone The anterior end of each free edge is attached to the petrous apex and the anterior and posterior clinoid processes The anterior and posterior petroclinoid the interclinoid fold. Between these folds is located the Oculomotor trigone Trochlear nerve enters the dura at the posterolateral edge of this triangle.

23. Oculomotor trigone Oculomotor N penetrates dura in central part of this ▲,trochlear N enters dura at posterolateral edge of this ▲ Trochlear N enters dura in the anteromedial edge of the tentorium (the 6 th N enters cavernous sinus by passing below petroclinoid ligament)

24. Anterior incisural space Cranial Nerves

25. Anterior incisural space Arterial relationships Anterior incisural space contains all components of circle of willis The ICA enters the anterior incisural space by passing along the medial surface of the anterior clinoid process and bifurcates below the anterior perforated substance The proximal part of the anterior cerebral artery also courses in the anterior incisural space MCA bifurcates in lateral part of Ant incisural space

26. Anterior incisural space Arterial relationships

27. Anterior incisural space Arterial relationships Post.comm A arises from posteromedial surface of ICA and courses medially & inferiorly. it is above & medial to 3 rd N;to join PCA at jn of P1-P2 segment Anterior choroidal A arises from posterior wall of ICA above origin of P com A & passes backward below optic tract

28. Anterior incisural space Arterial relationships The basilar artery ascends and gives rise to the PCA and SCA in the posterior part of the anterior incisural space

29. Anterior incisural space Arterial relationships Pcom arises from posteromedial surface of ICA and courses medially & inferiorly.it is above & medial to 3 rd N

30. Anterior incisural space Arterial relationships 3 rd n is b/w PCA & SCA.PCA courses around cerebral peduncle above 3 rd n

31. Anterior incisural space Venous relations The main venous trunk related to the anterior incisural space is the basal vein Basal vein originates below anterior perforated substance (anterior & middle cerebral vein) Basal vein courses below optic tract and b/w uncus & cerebral peduncle to enter middle incisural space The basal vein accompanies the PCA in the upper part of the crural and ambient cisterns and empties into the vein of Galen in the quadrigeminal cistern.

32. Anterior incisural space Venous relations

33. Middle incisural space Located lateral to brain stem Neural relations Medial wall-lateral surface of midbrain & upper pons Junction of Pons & midbrain is situated at level of free edge Lateral wall is formed by medial surface of temporal lobe-uncus& parahippocampal gyrus

34. Middle incisural space

35. Anterior/ventral Poterior/Dorsal Middle incisural space

36. Uncus commonly prolapses into incisura anteriorly Posterior to uncus, surface of temporal lobe facing middle incisural space is formed by SUBICULUM (rounded medial edge of parahippocampal gyrus) dentate gyrus and fimbria of fornix Middle incisural space extends below tentorium and communicates with cerebellomesencephalic fissure

37. Middle incisural space The roof of the middle incisural space has a narrow anterior part formed by the posterior part of the optic tract, and a wider posterior part formed by the inferior surface of the thalamus

38. Middle incisural space Cisternal relations Crural cistern is located b/w cerebral peduncle & uncus; opens posteriorly into ambient cistern Ambient cistern is bounded medially by mid brain & laterally by dentate gyrus, fimbria & subiculum. Contains PCA,trochlear nerves . Ambient cistern is continuous posteriorly with quadrigeminal cistern

39. Middle incisural space Cisterns Crural Ambient

40. Middle incisural space Neural relations 4 th and 5 th nerve are in close relation with Middle incisural space Trochlear N is most intimately related to free edge of tentorium incisura. trochlear N passes forward b/w PCA & SCA on the lateral margin of brain stem. It pierces the free edge in posterior part of oculomotor trigone.The PCA consistently courses above the trochlear

41. Middle incisural space Neural relations The trigeminal nerve courses in the infratentorial part of the middle incisural compartment It arises on the anterolateral aspect of the mid pons and passes above the petrous apex to enter Meckel's cave it is hidden below the free edge of tentorium incisura.

42. Middle incisural space Neural relations

43. Middle incisural space Arterial relations The major arteries in the middle incisural space are – Anterior choroidal PCA SCA

44. Middle incisural space Arterial relations Ant. Choroidal A enters middle incisural space below optic tract and passes through choroidal fissure to supply choroid plexus in temporal horn

45. Middle incisural space Arterial relations PCA enters middle incisural space by passing b/w cerebral peduncle & uncus. It has 4 segments P 1 segment extends from basilar bifurcation to jn with P com. P2A or crural segment or anterior part lies in crural cistern.P2P or posterior part or ambient segment lies in ambient cistern P3 segment is Quadrigeminal segment P4 segment is cortical segment – supplies temporal and occipital lobes

46. PCA parts

47. Middle incisural space Arterial relations

48. Middle incisural space Arterial relations - PCA

49. Middle incisural space Arterial relations - PCA

50. Middle incisural space Arterial relations

51. Middle incisural space Arterial relations - SCA Superior cerebellar A passes below the level of free edge; it passes above the trigeminal N and enters cerebello-mesencephalic fissure Middle incisural space is intimately related to temporal horn. some operative approaches to this space are directed through the temporal horn (temporal horn ends 3 cm from anterior pole of temporal lobe)

52. Middle incisural space – Venous relationships Venous relationships are relatively simple n this space The basal vein courses along the upper part of the cerebral peduncle to reach the posterior incisural space.

53. Posterior incisural space The posterior incisural space lies posterior to the midbrain and corresponds to the pineal region It has a roof, floor, anterior wall, lateral wall

54. Posterior incisural space Roof is formed by splenium Floor - anterosuperior part of the cerebellum and consists of vermis in the midline and the quadrangular lobules of the hemispheres laterally Anterior wall is formed by Quadrigeminal plate, pineal body, habenular complex Each lateral wall is formed by the pulvinar, crus of the fornix, and the medial surface of the cerebral hemispher

55. Quadrigeminal cistern Major cistern in the posterior incisural space - Quadrigeminal cistern It communicates above with the posterior pericallosal cistern ; I nferiorly into the cerebellomesencephalic fissure; I nferolaterally into the posterior part of the ambient cistern

56. Quadrigeminal cistern

57. Posterior incisural space – Arterial relations 2 arteries PCA & SCA The perforating branches of the PCA and SCA, and the medial posterior choroidal arteries supply the walls of the posterior incisural space . The PCAs supply the structures above the level of the lower margin of the superior colliculi The SCA s supply the structures below the upper margin of the inferior colliculi

58. Posterior incisural space – Venous relations The posterior incisural space has the most complex venous relationships in the cranium The internal cerebral and basal veins and many of their tributaries converge on the vein of Galen within this area The internal cerebral veins and the basal veins exit reach the posterior incisural space, where they join to form The vein of Galen The vein of Galen passes below the splenium to enter the straight sinus at the tentorial apex

59. Anatomy of deep veins Anterior septal vein +thalamostriate vein join to form ICV just behind foramen of monro. Angle formed by jn of thalamostriate vein and ICV-venous angle(acute angle)approximates site of foramen of Monro Both ICV and Basal vein of Rosenthal unite to form Vein of Galen below splenium in Superomedial part of quadrigeminal cistern Inferior sagittal sinus and Vein of Galen merge into Straight sinus – which drains into either of Tranverse sinus

60. Anatomy of deep veins

61. Tentorial arteries The tentorial arteries arise from three sources ICA (cavernous segment) SCA PCA

62. Tentorial arteries Cavernous segment of ICA → Meningohypophyseal trunk → Basal tentorial artery (Artery of Bernasconi & Cassinari) Cavernous segment of ICA → Inferolateral trunk → Marginal tentorial Artery (Artery of inferior cavernous sinus) SCA Meningeal branch PCA Tentorial branch

63. Tentorial herniation Descending Herniation-uncus & parahippocampal gyri herniate down Ascending Herniation-superior part of cerebellum herniate upward

64. Tentorial herniation Descending H erniation -3 types Anterior Posterior Complete

65. Tentorial herniation Anterior type -uncus herniates into interpeduncular & crural cisterns;later parahippocampal gyrus herniates Amygdaloid nucleus is involved with uncus in herniated mass Distortion & compression of midbrain reticular activating pathways cause ↓ level of consciousness Compression of ipsilateral cerebral peduncle-contralateral pyramidal signs

66. Tentorial herniation Distortion & compression of posterior hypothalamus cause cardiovascular,resp & thermoregulatory disturbances Pituitary stalk may be compressed against dorsum sella-DI 3 rd N courses b/w medial border of uncus & posterior petroclinoid fold;may be compressed here or b/w PCA & SCA Initially pupilloconstrictor fibres on superior surface of Nerve are compressed Later, somatic fibers to the extraocular muscles are paralysed.

67. Tentorial herniation Abducent nerve is stretched in subarachnoid space Obstruction of PCA may occur as it crosses the free edge PCA infarct-contralateral hemiplegia due to involvement of cerebral peduncle,LOC due to ischemia of midbrain reticular formation

68. Posterior type of tentorial herniation Posterior portion of parahippocampal & lingual gyrus may herniate into quadrigeminal cistern Tectal compression-vertical gaze disturbance occurs. PCA infarction-hemianopsia Basal vein & vein of galen may be compressed

69. Complete Tentorial herniation The complete type of herniation yields a combination of signs and symptoms observed with anterior and posterior herniations.

70. Kernohan's notch Compression of the ipsilateral cerebral peduncle causes contralateral pyramidal signs I f the lateral displacement of brainstem is severe, the contralateral cerebral peduncle may be forced against the free edge of tentorium, thus producing a groove on the peduncle called a Kernohan's notch , with ipsilateral pyramidal signs

71. Kernohan's notch phenomenon

72. Ascending herniation Due to posterior fossa mass lesion Superior part of cerebellar vermis and hemispheres herniate upward into quadrigeminal cistern Cerebellar infarction –compression of branches of SCA where they pass under free edge Vein of galen may be compressed against splenium

73. Operative considerations Anterior incisural space Nearly 95% of saccular aneurysms arise within anterior incisural space Aneurysms arising from part of circle of willis anterior to Liliequist memb. are approached via pterional craniotomy Aneurysms behind liliequist memb- Above dorsum-pterional or subtemporal Below dorsum-subtemporal craniotomy

74. Sectioning tentorium Incision in tentorium to expose interpeduncular & prepontine cisterns is just posterior to the point where trochlear N enters the free edge Avoid stretching trochlear N while retracting the free edge Trochlear N is the cranial N most frequently injured in middle incisural space Sectioning tentorium-use-to alleviate pressure on brainstem caused by incisural tumors that cannot be removed

75. The subtemporal approach with elevation of temporal lobe is useful to expose lesions in cisterns around incisura Venous sinuses are more commonly encountered in the posterior than anterior part of tentorium

76. Tentorial Meningioma 3 groups-lateral, medial & falcotentorial Blood supply-A of Bernasconi & cassinari from meningohypophysial trunk MRV should be done to note vein of Labbe, sigmoid sinus, transverse sinus and torcular heterophili

77. Tentorial Meningioma Yasargill’s clas’n T1 – anterior free tentorial notch T2- middle free tentorial notch T3-posterior free tentorial notch T4-involving intermediate surface T5-involving Torcula Herophili T6,T7 – from outer tentorial ring(ant,post) T8- Facotentorial meningiomas T4 T2 T3 T7 T5

78. Approaches to tentorial meningioma Sub temporal approach Sub occipital, retrosigmoid Fronto-temporal craniotomy +Zygomatic osteotomy (anterior sub-temporal +trans-sylvian approach) Combined posterior sub-temporal & pre-sigmoid approach

79. Complications for tentorial meningioma temporal lobe edema & contusion (pure sub-temporal approach for a lesion at incisura) Brain stem & cerebellar injury Cranial Nerve dysfunction-3,4,5

80. Outline The tentorial incisura provides the only communication between the supratentorial and infratentorial spaces. The area between the upper brainstem and the incisural edges is divided into the anterior, middle , and posterior incisural spaces

81. Outline The anterior incisural space contains all of the components of the circle of Willis and the bifurcation of the internal carotid and basilar arteries T he posterior incisural space contains the convergence of the internal cerebral and basal veins and many of their tributaries on the vein of Galen.

82. Outline The incisura is intimately related to the depths of the cerebrum and cerebellum, the first six cranial nerves and the upper brainstem.

83. BIBILLIOGRAPHY RHOTONS CRANIAL ANATOMY AND SURGICAL APPROACHES

84. Thankyou