Clivus 360°

1. Clivus 360 ° 20-6-2016 11.42 pm

2. Great teachers – All this is their work . I am just the reader of their books . Prof. Paolo castelnuovo Prof. Aldo Stamm Prof. Mario Sanna Prof. Magnan

3. For Other powerpoint presentatioins of “ Skull base 360° ” I will update continuosly with date tag at the end as I am getting more & more information click www.skullbase360.in   - you have to login to   slideshare.net  with Facebook account for downloading.

4. Sphenoid osteum

5. Sphenoid osteum present at the juction of upper 2/3 rd & lower 1/3 rd junction of Superior turbinate – this became very useful to me in extensive fungal sinusitis with polyposis & bleeding.

6. Three sequential indentations are made with the blunt end of the 4-mm microdebrider blade starting at the medial upper limit of the posterior bony choana and moving directly superiorly medial to the cut edge of the superior turbinate.

7. Basi occiput & basi sphenoid

8. Clivus Upper C livus Mid Clivus Lower Clivus

9. The “Ventral” Rule of Three - 3 turbinates codes to upper,middle , lower Clivus ...

10. Pneumatization of the sphenoid sinus

11. In conchal sphenoid surgical landmarks – 1. posterior end of vomer or keel of sphenoid tells about the position of pituitary 2. lateral boarder of posterior choana [ or MPP ]tells about paraclival carotid & sellar carotid C-SHAPE convex is lateral to this line 3. posterior lower boarder of vomer is at the junction of middle & lower 1/3 rd clivus & it is exactly at foramen lacerum –my understanding

12. Upper Clivus

13. Accoding to literature of lateral skull base - by Prof. Mario sanna - 1 . Upper clivus – Upto 6 th nerve entry dorello’s canal (petro- clival junction) 2. Middle clivus – from 6 th nerve to jugular foramen 3. Lower clivus – from jugular foramen to foramen magnum Lateral skull base Anterior skull base

14. According to literature of anterior skull base – The middle third clivus ( M. 1/3rd) begins at the sella floor ( SF) and extends to the floor of the sphenoid sinus (SSF), and the lower third (L. 1/3rd) extends from the floor of the sphenoid sinus to the foramen magnum ( FM). Lateral skull base Anterior skull base

15. Mid clivus is from “Floor of sella to Floor of sphenoid” – best Mneumonic – is nothing but clivus between paraclival carotids

16. Cadaveric dissection demonstrating that instrumentation without adequate removal of the floor of the sphenoid sinus results in a straight instrument being driven high into the middle third of the clivus beneath the pituitary fossa. Removal of the floor of the sphenoid sinus ( SS ) will allow access to the junction of the posterior sphenoid floor and adjacent clivus .

17. Cadaveric dissection in the plane between the periosteal layer of dura and the meningeal layer of dura ( MD ) covering the right side of the pituitary gland. The pituitary dentate ligaments ( DL ) can be clearly visualized. CS , cavernous sinus.

18. Pituitary Translocation for Access to the Upper Third of the Clivus Cadaveric dissection of the sphenoid sinus demonstrating the removal of bone over the anterior genu of the intracavernous carotid arteries, sella , tuberculum sella , and the posterior half of the planum sphenoidale ( PS ). CCA , anterior genu of the intracavernous carotid artery; IIS , inferior intercavernous sinus; SIS , superior intercavernous sinus; P , pituitary gland. Fig. 19.23 Cadaveric dissection demonstrating the osteotomies at the base of the posterior clinoids ( PC ) for separation with the body of the dorsum sella ( DS ). P. CCA , posterior genu of the intracavernous carotid artery; PCA , paraclival carotid artery; ICCA , intracranial carotid artery; BA , basilar artery; PL , posterior lobe of the pituitary gland; AL , anterior lobe of the pituitary gland.

19. Cadaveric dissection demonstrating the osteotomies at the base of the posterior clinoids ( PC ) for separation with the body of the dorsum sella ( DS ). P. CCA , posterior genu of the intracavernous carotid artery; PCA , paraclival carotid artery; ICCA , intracranial carotid artery; BA , basilar artery; PL , posterior lobe of the pituitary gland; AL , anterior lobe of the pituitary gland.

20. Cadaveric dissection image demonstrating the close anatomical relationship of the posterior clinoid ( PC ) with both the intracranial carotid artery ( ICCA ) and the posterior genu of the intracavernous carotid artery ( P. CCA ). AL , anterior lobe of the pituitary gland ; PL , posterior lobe of the pituitary gland; BA , basilar artery. green dotted triangle area for entry of the endoscope into the interpeduncular fossa

21. Normal pituitary YELLOW in color Anterior & posterior lobe of pituitary

22. ICAc cavernous portion of the internal carotid artery, IPS inferior petrosal sinus, PAp petrous apex, SPCG sphenopetroclival gulf, cVIcn cisternal segment of the abducens nerve, gVIcn gulfar segment of the abducens nerve, pVIcn petrosal segment of the abducens nerve, white asterisks dura of the posterior cranial fossa – The gulfar segment can be identified at the intersection of the sellar floor and the proximal parasellar internal carotid artery (ICA) (Barges- Coll et al. 2010 ). Upper clivus – Upto 6 th nerve entry dorello’s canal (petro- clival junction)

23. 1. 6 th N. crossing carotid at Petro- clival junction when viewing in lateral skull base - The lateral aspect of the parasellar & paraclival carotid junction is crossed by the abducent nerve ( VI ) at the entrance of both [ 6 th nerve & carotid ] structures into the cavernous sinus. 2. The gulfar segment can be identified at the intersection of the sellar floor and the proximal parasellar internal carotid artery (ICA) (Barges- Coll et al. 2010 ).

24. Pregnant of upper clivus is Sella

25. Endoscopic view of the fl oor of the third ventricle. The dorsum sellae and the upper premesencephalic (mammillary bodies) region are evident. DS dorsum sellae , IR infundibular region (infundibulum), MBs mammillary bodies, PS pituitary stalk , ThV fl fl oor of the third ventricle

26. 0° endoscope. In the next pictures the retrosellar area is presented when an endoscope is inserted behind the pituitary stalk and orientated downwards (arrows ). The dorsum sellae is outlined with a dotted line . - From Atlas of Endoscopic Anatomy for Endonasal lntracranial Surgery ; Paolo Cappabianca

27. 30° endoscope. After the introduction of a downward orientated endoscope behind the dorsum sellae the basilar tip is visualized. PCoA = posterior communicating artery, SCA = superior cerebellar artery, P1-P2 = posterior cerebral artery .

28. 30° endoscope. Right side. closer view. PCoA = posterior communicating artery . SCA = superior cerebellar artery. P1 = posterior cerebral artery.

29. 30° endoscope. Left side. closer view. SCA = superior cerebellar artery. P1-P2 = posterior cerebral artery. PCoA = posterior communicating artery.

30. ENDOSCOPIC ENDONASAL PITUITARY TRANSPOSITION APPROACH TO THE SUPERIOR CLIVUS - Rare basilar or PCA aneurysms could be accessed as well , though this requires significant experience and very careful patient selection. A. Preoperative CTA showing a three-dimensional reconstruction view of a large PCA aneurysm causing an oculomotor nerve palsy. B. Intraoperative view of the aneurysm before clipping . C. Intraoperative view of the aneurysm after clipping. Intraoperative angiogram showing complete obliteration of the aneurysm and patency of normal basilar apex branches.

31. A . Preoperative CTA showing a three-dimensional reconstruction view of a large PCA aneurysm causing an oculomotor nerve palsy. B . Intraoperative view of the aneurysm before clipping. C . Intraoperative view of the aneurysm after clipping. Intraoperative angiogram showing complete obliteration of the aneurysm and patency of normal basilar apex branches.

32. Cadaveric dissection image taken with a 30-degree endoscope following removal of the superior third of the clivus , visualizing the small trochlear nerve seen running along the tentorial membrane edge.

33. Pituitary transposition (Upper clivus ): Take special care to identify and preserve the superior hypophyseal arteries. (SHA) Extradural: Dissect the pituitary gland from the remainingsellar floor and posterior wall. Lift the pituitary gland, expose and drill out theposterior clinoids . Intradural : Open the sellar dura anteriorly and dissect the dura from the tunica. Transect the ligaments that join these two layers and the inferior hypophyseal arteries. Divide the diahragm exposing the stalk of the pituitary.Transpose the gland superiorly over the chiasm.

34. Endoscopic view with 45º lens after pituitary transposition. MB: mammillary bodies; PCA: posterior cerebral artery; PCoA : posterior communicating artery; SCA: superior cerebellar artery; VA: vertebral artery; III: third cranial nerve

35. Mid Clivus

36. Mid clivus is from “Floor of sella to Floor of sphenoid” – best Mneumonic – is nothing but clivus between paraclival carotids

37. Lower half of paraclival carotid - caudal part, the lacerum segment of the paraclival carotid   ”The unsolved surgical problem remains the medial wall of the ICA at the level of the anterior foramen lacerum , until now unreachable with the available surgical approaches."  - In lateral skull base by Prof. Mario sanna – this unreachable is Carotid- Clival window which is accessable in Anterior skull base Infrapetrous Approach Carotid- Clival window – Mid clivus a. Petrosal face b.Clival face

38. 1. Mid clivus – from floor of sella to floor of sphenoid sinus 2. From carotid- clival window we can reach petrous apex by infra-petrous approach 3. Mid clivus is in between paraclival carotids

39. 1. Mid clivus – from floor of sella to floor of sphenoid sinus 2. From carotid- clival window we can reach petrous apex by infra-petrous approach 3. Mid clivus is in between paraclival carotids

40. 1. Mid clivus – from floor of sella to floor of sphenoid sinus 2. From carotid- clival window we can reach petrous apex by infra-petrous approach 3. Mid clivus is in between paraclival carotids

41. JT = jugular tubercle separates the hypoglossal canal from Jugular foramen

42. Jugular tubercle [ JT ] AICA antero -inferior cerebellar artery, ASC anterior semicircular canal, BA basilar artery, HC hypoglossal canal, IAC internal acoustic canal, ICAh horizontal portion of the internal carotid artery, JT jugular tubercle, LCNs lower cranial nerves, LSC lateral semicircular canal, P pons , PICA postero -inferior cerebellar artery, PSC posterior semicircular canal, VIcn abducens nerve, VIIcn facial nerve, white arrow vestibolocochlear nerve

43. The foramen lacerum (FL) is located lateral to the floor of the sphenoid sinus at the level of the spheno -petro- clival confuence . JT jugular tubercle, HC hypoglossal canal – addFig 3.78 also

44. Pontomedullary junction = Vertebro-basillar junction = Junction of Mid clivus & Lower clivus = foramen lacerum area The pontomedullary junction. The vertebral artery junction is at the level of the junction of the inferior and midclivus . The basilar artery runs in a straight line on the surface of the pons. The exit zones of the hypoglossal and abducent nerves are at the same level. The abducent nerve exits from the pontomedullary junction, and ascends in a rostral and lateral direction toward the clivus .

45. Very rare specimen..The vbj is far inferior to floor of sphenoid sinus

46. Cadaveric dissection of the middle third of the clivus with removal of the basilar plexus and exposing the dura . The abducens nerves ( CN VI ) can be seen bilaterally as they perforate the meningeal dura and become the interdural segments of CN VI. CS , cavernous sinus; PCA , paraclival carotid arteries; P , pituitary gland.

47. Clival recess

48. See the relationship between lower boarder of posterior end of vomer & clivus – vomer lower boarder is at junction of mid & lower clivus – my understanding

49. http://www.neurosurgicalapproaches.com/2013/08/25/

50. Anterior cranial fossa dura Posterior cranial fossa dura

51. Lower Clivus

52. Groove for medulla on Lower C livus [ = Basi Occiput ]

53. 1 . The HC divides the condylar region into the tubercular compartment (superior) and the condylar compartment (inferior). Tubercular compartment contains LPT lateral pharyngeal tubercle , PT pharyngeal tubercle , 2. The SCG [Supracondylar groove] represents a reliable landmark for hypoglossal canal (HC) identification (red arrow) ( Morera et al. 2010 ) .

54. The tubercular compartment corresponds to the Jugular tubercle ( JT ) Line along the lateral pharyngeal tubercle [ LPT ] passes through Jugular tubercle [ JT ] – so when you are drilling LPT in anterior skull base you will land up on JT . LPT lateral pharyngeal tubercle, OC occipital condyle, PT pharyngeal tubercle, SCG supracondylar groove Jugular tubercle ( JT )

55. Line along the lateral pharyngeal tubercle [ LPT ] passes through Jugular tubercle [ JT ] – so when you are drilling LPT in anterior skull base you will land up on JT . Red rings = hypoglossal canals , yellow ring = pharyngeal tubercle [ PT ] , blue rings = lateral pharyngeal tubercle [ LPT]

56. Line along the lateral pharyngeal tubercle [ LPT ] passes through Jugular tubercle [ JT ] – so when you are drilling LPT in anterior skull base you will land up on JT . yellow ring = pharyngeal tubercle [ PT ] , blue rings = lateral pharyngeal tubercle [ LPT] , green ring = Jugular tubercle

57. Hypoglossal canals From front – through nose From back

58. Lower clivus devided into 1. tubercular compartment [ Above red line ] 2. condylar compartment [ Below red line ] Hypoglossal canal present at the junction of anterior 1/3 rd & posterior 2/3 rd

59. Lower clivus + petrous bone [ base ] Petrous bone devided into three 1/3rds

60. Lower clivus + petrous bone [ base ] + Zygomatic bone Petrous bone devided into three 1/3rds

61. Lateral skull base view – observe the petrous apex

62. Lower clivus + petrous apex in anterior skull base 1. observe the petrous apex in both views 2. hypoglossal canal medial to parapharyngeal carotid & jugular fossa

63. ICA Vertebro-basillar

64. 1. 3th nerve between PCA & SCA 2. 4 th nerve coming from dorsal brain stem passes above SCA [ some times SCA has two branches] 3. 6 th nerve originates at VBJ [ Vertebro-basillar junction ] . 6 th nerve may have two rootlets of origin , one above & one below the AICA 4. In 30 % of cases AICA passes in between 7 th & 8 th nerves 5. PICA passes between two bundles of 12 th nerve & between two roots of 11 th nerve [ 11c = 11 th cervical , 11s = 11 th spinal root ] 6. The exit zones of the 6 th and 12 th nerves are at the same level [ same vertical line when view from Transclival approah ( through lower clivus ) ] 7. 11 th nerve behind left vertebral artery at cervico -medullary junction . 11 th is closely related to the vertebral artery (VA) at the point of dural entrance

65. 1. 3th nerve between PCA & SCA 2. 4 th nerve coming from dorsal brain stem passes above SCA [ some times SCA has two branches] 3. 6 th nerve originates at VBJ [ Vertebro-basillar junction ] . 6 th nerve may have two rootlets of origin , one above & one below the AICA 4. In 30 % of cases AICA passes in between 7 th & 8 th nerves 5. PICA passes between two bundles of 12 th nerve & between two roots of 11 th nerve [ 11c = 11 th cervical , 11s = 11 th spinal root ] 6. The exit zones of the 6 th and 12 th nerves are at the same level [ same vertical line when view from Transclival approah ( through lower clivus ) ] 7. 11 th nerve behind left vertebral artery at cervico -medullary junction . 11 th is closely related to the vertebral artery (VA) at the point of dural entrance

66. 1. 3th nerve between PCA & SCA 2. 4 th nerve coming from dorsal brain stem passes above SCA [ some times SCA has two branches] 3. 6 th nerve originates at VBJ [ Vertebro-basillar junction ] . 6 th nerve may have two rootlets of origin , one above & one below the AICA 4. In 30 % of cases AICA passes in between 7 th & 8 th nerves 5. PICA passes between two bundles of 12 th nerve & between two roots of 11 th nerve [ 11c = 11 th cervical , 11s = 11 th spinal root ] 6. The exit zones of the 6 th and 12 th nerves are at the same level [ same vertical line when view from Transclival approah ( through lower clivus ) ] 7. 11 th nerve behind left vertebral artery at cervico -medullary junction . 11 th is closely related to the vertebral artery (VA) at the point of dural entrance

67. 1. Laceral carotid & jugular tubercle & lower cranial nerves 9 th ,10 th ,11 th are in the same line . 2. hypoglossal canal present between occipital condyle/foramen magnum & jugular tubercle

68. 1. Laceral carotid & jugular tubercle & lower cranial nerves 9 th ,10 th ,11 th are in the same saggital line . 2 . hypoglossal canal present between occipital condyle/foramen magnum & jugular tubercle 3. PICA passes between two bundles of 12 th nerve & between two roots of 11 th nerve [ 11c = 11 th cervical , 11s = 11 th spinal root ] & encirlces lower cranial nerves 9 th ,10 th ,11 th

69. Trans clival trans odontoid trans tubercular view of brainstem and cranial nerves....note sharp oblique course of 6 nerve and two trunks of 12 nerve which joins to form single trunk in hypoglossal canal...a dorsal clival branch of meningohypophyseal trunk is seen along six nerve close to dorello canal...AICA is seen going towards IAM.

70. Coronal cut – hypoglossal canal

71. Inferior clival line (Fernandez-Miranda et al. 2012 ) The longus capitis and rectus capitis anterior muscle attach on the inferior surface of the clivus . Below the RCAM the occipito -cervical joint capsule lies. The area of attachement of the RCAM has been named inferior clival line (Fernandez-Miranda et al. 2012 ) and correspond to the SCG [supracondylar groove ] (that is a landmark for the hypoglossal canal). AAAM anterior atlanto-axial membrane, AAOM anterior atlanto-occipital membrane, AIM anterior intertrasversarius muscle, Cl clivus , C1 atlas, C1TP transverse process of C1, C2 axis, ET eustachian tube, JF jugular foramen, JT jugular tubercle, HC hypoglossal canal, ICAc cavernous portion of the internal carotid artery, LCapM longus capitis muscle, LColM longus colli muscle, PG pituitary gland, RCAM rectus capitis anterior muscle, RCLM rectus capitis lateralis muscle, blue-sky arrow apical ligament, green arrow external ori fi ce of the hypoglossal canal, black arrow lateral atlanto -occipital ligament, black asterisk foramen lacerum

72. The area of attachement of the RCAM has been named inferior clival line (Fernandez-Miranda et al. 2012 ) and correspond to the SCG [supracondylar groove ] ( that is a landmark for the hypoglossal canal ). SCG = Supracondylar groove – is an important landmark to hypoglossal canal

73. When we are drilling lower clivus – lateral to hypoglossal canal we get Jugular fossa

74. Jugular fossa is just lateral to hypoglossal canal

75. Cadaveric dissection image demonstrating structures seen following dissection of the lower third of the clivus . Note how the basilar arteries and vertebral arteries can be extremely tortuous in their course.

76. Cadaveric dissection image showing the hypoglossal nerve exiting the hypoglossal foramen with its corresponding vein that communicates the internal jugular vein with the basilar plexus. HC , hypoglossal canal; CN XII , hypoglossal nerve and rootlets; FM , foramen magnum; VA, vertebral artery; PICA , posterior inferior cerebellar artery; BA , basilar artery; CN X , vagus nerve.

77. Cadaveric dissection with image taken just above the skeletonized hypoglossal canal ( HC ) at the cerebellopontine angle. The anterior inferior cerebellar artery ( AICA ) can be seen intimately associated with the vestibulocochlear nerve ( CN VIII ), facial nerve ( CN VII ), and the nervus intermedius ( NI ). The posterior inferior cerebellar artery ( PICA ) can be seen running between the vagus ( CN X ) and spinal and cranial portions of the accessory nerves ( CN XI – S , CN XI – C ).

78. Cadaveric dissection image taken following dissection of the right lower third of the clivus . As the posterior inferior cerebellar artery ( PICA ) courses from the vertebral artery ( VA ) it frequently runs through the rootlets that make up the hypoglossal nerve ( CN XII ). It may tent these rootlets as it courses to the cerebellomedullary fissure to run intimately with the cranial nerves IX – XI. CN X , vagus nerve ; HC , hypoglossal canal; IPS , inferior petrosal sinus; BA , basilar artery; FM , foramen magnum; A. AOM , anterior atlanto -occipital membrane .

79. The hypoglossal nerve do not exit with VA. It can have maximum 3 outlets . On the contrary , C1 roots exit with the VA.

80. Through endoscopic lateral skull base - The curved vertebral artery displaces and stretches the hypoglossal nerve fibers. Through anterior skull base

81. HC = hypoglossal canal , JT= Jugular Tubercle

82. Transoral approach to SUPERO-MEDIAL Parapharyngeal tumors – incision anterior to anterior pillar of tonsil

83. Hypoglossal is just behind the upper end of parapharyngel carotid – very easy way to identify 12 th nerve in paraphayrngeal space – Dr.Satish jain

84. FCB & JT & LCNs are at same level from anterior to posterior FCB = Fibrocartilago basalis , JT = Jugular tubercle , LCNs Lower cranial nerves ( = 9 th , 10th, 11 th )

85. In infrapetrous approach there are chances of injury to 6 th nerve [ in dorello’s canal medial to paraclival carotid ] & 12 th nerve

86. Posterior cranial fossa (jugular and hypoglossal areas); vision obtained with a 45° endoscope through a clival window AICA anteroinferior cerebellar artery, BA basilar artery, IO inferior olive, LA labyrinthine artery , PCA posterior cerebral artery, PcomA posterior communicating artery, PICA posteroinferior cerebellar artery, POV preolivary vein, RPA recurrent perforating artery, SCA superior cerebellar artery , SPV superior petrosal vein , VA vertebral artery , IIIcn oculomotor nerve , Vcn trigeminal nerve, VIcn abducens nerve, VIIcn facial nerve, VIIIcn vestiboloacoustic ( statoacoustic ) nerve , IXcn glossopharyngeal nerve, Xcn vagus nerve, XIIcn hypoglossal nerve The LA usually originates from the AICA, rarely directly from the BA. It feeds the inner ear. AICA and SCA course through the cerebellopontine cistern. AICA enters the lower part of cerebellopontine cistern and it usually bifurcates into its rostral and caudal trunks within the cistern. PICA origins from the VA, near the inferior olive, and passes posteriorly around the medulla. It could pass rostral , caudal or even between the rootlets of the hypoglossal nerve. RPA(s ) are arteries that present a recurrent course and reach the root entry zone of the VII and VIII cns . They send branches to these nerves and to the brainsterm around the root entry zone.

87. Intracranial hypoglossal region. Anterior endoscopic transnasal-transclival vision is compared with a posterior retrosigmoid endoscopic one JF jugular foramen, JT jugular tubercle, IO inferior olive, PICA posteroinferior cerebellar artery , VA vertebral artery, IXcn glossopharygeal nerve, Xcn vagus nerve, XIcnCR cervical roots of accessory nerve, XIcnSR spinal roots of accessory nerve, XIIcn hypoglossal nerve Cranial nerves IX and X present a close relationship with the fi rst portion of the PICA. They are protected by the arachnoid membrane (Roche et al. 2008 ) . The roots of cranial nerve XIcn from the spine pass through the foramen magnum posterior to the vertebral artery. Within the hypoglossal canal, XIIcn is surrounded by a venous plexus and dural and arachnoid sheets. Branches of the ascending pharyngeal artery coursing through the hypoglossal canal are seen in about 50 % of cases ( Lang 1995 ) . Also branches from the posterior meningeal artery have been described ( Janfaza and Nadol 2001 ). The transcisternal vein to the area of the JF can be seen. Also, veins to the hypoglossal canal can be present. The hypoglossal nerve do not exit with VA. It can have maximum 3 outlets. On the contrary , C1 roots exit with the VA.

88. Nerves and vessels of the posterior cranial fossa. (a) Basilar tip region, endoscopic view (b) Right cerebellopontine angle, endoscopic view from anterior. (c) Right laterobulbar region, endoscopic intracranial view. (d) Three-dimensional reconstruction of the posterior cranial fossa. AICA , anteroinferior cerebellar artery; BA, basilar artery; DV, Dandy’s vein; Fl , flocculus ; IIIcn (CS), intracavernous portion of the oculomotor nerve; IIIcn , oculomotor nerve; IO, inferior olive; IXcn , glossopharyngeal nerve; IX–X, glossopharyngeal and vagus nerves; LA , labyrinthic artery; LPMVN, lateropontomesencephalic vein network; P1, posterior cerebral artery (first segment); P2, posterior cerebral artery (second segment); PcomA , posterior communicating artery; PICA, posteroinferior cerebellar artery; POV, preolivary vein; PV , peduncular vein; RPA, recurrent perforating artery; SCA, superior cerebellar artery; SPV, superior petrosal vein; TGAs, thalamogeniculate arteries; TPAs, thalamoperforating arteries; VA, vertebral artery; Vcn , trigeminal nerve; VIcn , abducens nerve; VII– VIIIcn , facial nerve and vestibuloacoustic nerve; VIIcn , facial nerve; VIIIcn , vestibuloacoustic nerve; X/ XIcn , vagus and accessory nerves ; XIcn , accessory nerve; XIIcn , hypoglossal nerve.

89. TPV & LAPMVs , PMedSV unite to form SPV AICA anteroinferior cerebellar artery, BA basilar artery, LPMVN lateropontomesencephalic venous network, PBs pontine branches, PcomA posterior communicating artery, PICA posteroinferior cerebellar artery, PMedSV pontomedullary sulcus vein, SCA superior cerebellar artery, SPV superior petrosal vein, TPAs talamoperforating arteries, TPV transverse pontine vein, IIIcn oculomotor nerve, Vcn trigeminal nerve, VIcn abducens nerve, VIIcn facial nerve, VIIIcn vestibulo -cochlear ( statoacoustic ) nerve

90. PICA passes between two bundles of 12 th nerve The endoscope is focusing on the hypoglossal nerve area. The posterior inferior cerebellar artery arises from the vertebral artery in the background, and runs between the two bundles of the hypoglossal nerve.

91. PICA can be seen running between the vagus ( CN X )

92. PICA can be seen running between spinal and cranial portions of the accessory nerves ( CN XI – S , CN XI – C ). Endoscopic lateral skull base Endoscopic anterior skull base Lateral skull base – far lateral approach

93. PICA passes between two bundles of 12 th nerve & between two roots of 11 th nerve Cadaveric dissection image demonstrating the posterior inferior cerebellar artery ( PICA ) running between the vagus ( CN X ) and the cranial accessory nerve rootlets ( CN XI-C ) at the position where the nerves exit the brainstem. CN VII , facial nerve; CN VIII , vestibulocochlear nerve; NI , nervus intermedius ; CN IX , glossopharyngeal nerve; CN XI-S , spinal accessory nerve The tip of the endoscope lies between the acousticofacial nerve bundle and the anterior inferior cerebellar artery . The posterior inferior cerebellar artery arises from the vertebral artery, runs between the root fibers of the hypoglossal nerve , and forms a loop below the roots of the lower cranial nerves , before coursing in a posterior direction.

94. Transcochlear approach leads to Mid clivus above foramen lacerum [ FL ] & lower clivus below foramen lacerum [ FL ] AAAM anterior atlanto-axial membrane, AAOM anterior atlanto-occipital membrane, AIM anterior intertrasversarius muscle, Cl clivus , C1 atlas, C1TP transverse process of C1, C2 axis, ET eustachian tube, JF jugular foramen, JT jugular tubercle, HC hypoglossal canal, ICAc cavernous portion of the internal carotid artery, LCapM longus capitis muscle, LColM longus colli muscle , PG pituitary gland, RCAM rectus capitis anterior muscle, RCLM rectus capitis lateralis muscle , blue-sky arrow apical ligament, green arrow external ori fi ce of the hypoglossal canal, black arrow lateral atlanto -occipital ligament, black asterisk foramen lacerum

95. Note CL [ Mid clivus above FL & lower clivus below FL ] in these photos after drilling of cochlea

96. Note CL [ Mid clivus above FL & lower clivus below FL ] in these photos after drilling of cochlea The clivus bone (CL) can be seen medial to the internal carotid artery (ICA). JB Jugular bulb In the lower part of the approach, the glossopharyngeal nerve (IX) can be seen. V Trigeminal nerve, VIII Cochlear nerve, AICA Anterior inferior cerebellar artery, CL Clivus bone, DV Dandy’s vein, FN Facial nerve, FN(m) Mastoid segment of the facial nerve, FN(t) Tympanic segment of the facial nerve, GG Geniculate ganglion, ICA Internal carotid artery, JB Jugular bulb, MFD Middle fossa dura , SCA Superior cerebellar artery, SS Sigmoid sinus

97. Note CL [ Mid clivus above FL & lower clivus below FL ] in these photos after drilling of cochlea BT- basal turn of the cochlea Fig. 8.34 The bone medial to the internal carotid artery (ICA) has been drilled and the clivus bone (CL) has been reached. FN Facial nerve, JB Jugular bulb

98. Note CL [ Mid clivus above FL & lower clivus below FL ] in these photos after drilling of cochlea Note cochlear aqueduct [ CA ] Here ICA is vertical part of carotid infront to cochlea – this is not paraclival carotid

99. Note CL [ Mid clivus above FL & lower clivus below FL ] in these photos after drilling of cochlea

100. Note CL [ Mid clivus above FL & lower clivus below FL ] in these photos after drilling of cochlea Note the contralateral vertebral artery [ CVA ] in below photo

101. Mid clivus above FL & lower clivus [ CL ] below FL in Infratemporal fossa approach

102. ITFA with Transcondylar [ = TC ] Transtubercular [ = TT ] approach Here Transcondylar is through Occipital Condyle ; Transtubercular is through Jugular tubercle & lateral pharyngeal tubercle

103. Endoscopic endonasal view of a cadaveric dissection showing transection of the right eustachian tube (ET) attachment to foramen lacerum (FL). The hypoglossal nerve (XII) enters the hypoglossal canal just deep to the ET and separates the occipital condyle (OC) and the jugular tubercle (JT). (BA, basilar artery; ICA, internal carotid artery [ paraclival segment]; IPS, inferior petrosal sinus; VN, vidian nerve.) B. Endoscopic endonasal view of cadaveric dissection showing the parapharyngeal internal carotid artery (ICA) and jugular foramen (JF) following transection and removal of the eustachian tube. (BA, basilar artery; IPS, inferior petrosal sinus; FL, foramen lacerum ; JT, jugular tubercle; OC, occipital condyle; XII, hypoglossal nerve.)

104. Note 12 th nerve in between JT ( Jugular tubercle ) & OC ( Occipital condyle ) in both lateral & anterior skull base Lateral skull base Anterior skull base

105. Hypoglossal is just behind the upper end of parapharyngel carotid – very easy way to identify 12 th nerve in paraphayrngeal space – Dr.Satish jain

106. ITF-A + Transcondylar , transtubercular extension improves posteroinferolateral and medial exposure.

107. Comparison of classic ITFA (zone delimited by the red line) and ITFA with transcondylar – transtubercular extension ( zone delimited by the blue line ). * jugular process of the occipital condyle , CF carotid foramen , DR digastric ridge , JF jugular foramen , MT mastoid tip . Note hypoglossal nerve at anterior 1/3 rd & middle 1/3 rd junction .

108. Extreme lateral extension [ Far-lateral – Transcondylar ] approach AFL anterior foramen lacerum , C1 atlas , CO cochlea , ICA internal carotid artery , IJV internal jugular vein , Lv vein of Labbé , M mandible , mma middle meningeal artery OC occipital condyle , pc clinoid process , pp pterygoid plate , sph sphenoid sinus , sps superior petrosal sinus , TA transverse process of the atlas , TS transverse sinus , V2 maxillary branch of the trigeminal nerve , V3 mandibular branch of the trigeminal nerve , za zygomatic arch , VA vertebral artery , VII facial nerve , IX glossopharyngeal nerve , XI spinal accessory nerve , XII hypoglossal nerve Far-lateral approach further extends posteroinferolateral exposure Schematic illustration of the extreme lateral approach (ELA )

109. For mid clivus – transcochlear approah & For lower clivus – far lateral / transcondylar approach OR ITF-A + TC + TT From decision making of Mario sanna lateral skull base book

110. The 6 linear landmarks of the PCF superimposed on a midsagittal T1-weighted MR imaging from a patient with CMI: herniation (HR), McRae line (MC), clivus (CL), Twining line (TW), cerebellum (CR), and supraocciput (SO). http://www.ajnr.org/content/34/9/1758.figures-only?cited-by=yes&legid=ajnr;34/9/1758

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