In this chapter, the anatomy of the anterolateral skull base, including the lateral wall of the cavernous sinus, is explored. An understanding of this anatomy is essential for planning surgeries in and around the cavernous sinus. In this chapter, the left cavernous sinus is dissected.
Key Steps
Step 1. Separation of dura propria from lateral wall of cavernous sinus (Fig. 8.2)
Step 2. Separation of dura propria from the lateral loop (Fig. 8.6)
Step 4. Exposure of the gasserian ganglion (Fig. 8.15)
Step 5. Opening of Parkinson’s triangle (Fig. 8.17)
Step 6. Identification of abducens nerve (Fig. 8.19)
Illustrated Steps with Commentary
Fig. 8.1 Superolateral wall of the cavernous sinus.This exposure of the left cavernous sinus begins with an extra-dural dissection of the dura from the superior orbital fissure and the floor of the middle fossa. The anterior clinoid process has already been removed (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion). (COM, carotico-oculo-motor membrane; GG, gasserian ganglion; ON, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 8.2 (Step 1) Carotico-oculomotor membrane.The dura propria is separated from the lateral wall of the cavernous sinus. The oculomotor nerve, trochlear nerve, and V1 are encased in the lateral wall of the cavernous sinus. The C3 portion of the internal carotid artery is covered by the carotico-oculomotor membrane. (COM, carotico-oculomotor membrane; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve])Fig. 8.3 Bony protrusion over lateral loop (midsubtemporal tubercle).The dura is dissected from the anterior tip of the bony middle fossa. A bony protrusion of the middle cranial fossa wall is usually seen lateral to the lateral loop. This mid-subtemporal tubercle is a useful landmark for finding the lateral loop at the time of surgery. The lateral loop is the web between the V3 and the V2 fibers. (AE, arcuate eminence; GSPN, greater superior petrosal nerve; LL, lateral loop; MSR, mid-subtemporal ridge; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.4 Bony protrusion over lateral loop.The bony protrusion, the mid-subtemporal tubercle, is seen anterior and between the foramen rotundum and foramen ovale. The other landmark useful for finding the foramen ovale is the foramen spinosum. Practically, the middle meningeal artery can be followed to the foramen spinosum, and the foramen spinosum guides the surgeon to the foramen ovale. (GSPN, greater superior petrosal nerve; LL, lateral loop; MMA, middle meningeal artery; MSR, mid-subtemporal ridge; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.5 Skeletonized sphenoid sinus.The sphenoid sinus can be entered medial to the second division of the trigeminal nerve (V2). The surgeon must be careful when drilling the bone from around V2 as an opening in the sphenoid sinus can result in a troublesome CSF leak. A light has been placed in the sphenoid sinus to illuminate that sinus in this photo. (LL, lateral loop; MMA, middle meningeal artery; SS, sphenoid sinus; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.6 (Step 2) Lateral loop medial to bony protrusion.As the dura propria is separated from V2, V3, and the lateral loop of the trigeminal nerve. Venous bleeding will invariably be encountered. The bleeding channels are a part of the rich anastamosis between the pterygoid plexus and the cavernous veins. Cauterizing these channels may result in facial paresthesias. It is best to pack these channels with oxidized cellulose, apply gentle pressure, and wait. Recalcitrant bleeding can be stopped with oxidized cellulose and fibrin glue. (LL, lateral loop; MSR, mid-subtemporal ridge; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.7 The dura propria is separated from V2 and V3.The initial separation of the dura propria from the trigeminal nerve is done with a sharp knife. The dissection can usually be continued with a blunt dissector. Usually the dura attachment on the lateral side of V3 will need to be cut with a knife. (C4, C4 portion of the internal carotid artery; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.8 The dura propria is separated from the branches of the trigeminal nerve and the trigeminal ganglion.A blue latex injected into the veins and cavernous sinus has been removed to better demonstrate the anatomy. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; GSPN, greater superior petrosal nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.9 Relationship with posterior clinoid process and intradural oculomotor nerve.The posterior loop of the carotid artery, the posterior clinoid, and the intradural oculomotor nerve are all seen rostral to V1. The oculomotor nerve will enter its intradural tunnel by piercing a triangular region of dura that is anchored by the anterior clinoid, posterior clinoid, and petrous bone tip. (C2, C2 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; GSPN, greater superior petrosal nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve ; VI, abducens nerve)Fig. 8.10 (Step 3) Opening of the oculomotor foramen.The oculomotor foramen leads into a canal. The oculomotor nerve runs through this canal, which can be opened to free the nerve. Freeing the oculomotor nerve is a useful maneuver when approaching basilar tip aneurysms, via either a subtemporal or a pterional route. The length of the canal that can be opened is limited by the crossing of the trochlear nerve over the oculomotor nerve. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve)Fig. 8.11 Division of the oculomotor nerve in the oculomotor canal.The oculomotor nerve has already divided into its superior and inferior portions in the oculomotor canal. The two divisions are separated by a thin membranous structure. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve)Fig. 8.12 Skeletonization of the posterior genu of the internal carotid artery.The posterior genu of the internal carotid artery connecting the C5 and C4 portions of the carotid artery can be seen between the trochlear nerve and V1 through the outer membrane of the cavernous sinus. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve])Fig. 8.13 Superior orbital fissure.The oculomotor nerve, the trochlear nerve, V1, and the abducens nerve pass through the superior orbital fissure. The oculomotor nerve runs medial to the tip of the anterior clinoid process. The trochlear nerve runs lateral to the oculomotor nerve. It passes over the top of CN III as it enters the orbit. The abducens nerve and V1 can be seen passing over the oculomotor nerve. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve; SOV, superior ophthalmic vein; V1, ophthalmic nerve [first division of the trigeminal nerve])Fig. 8.14 Complete cavernous sinus exposure.The oculomotor, the trochlear, the trigeminal nerve and its divisions, and the posterior bend of the internal carotid artery are seen through the true cavernous membrane that covers the cavernous sinus. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.15 (Step 4) Exposure of the gasserian ganglion.The gasserian ganglion lies in the dural pocket commonly called Meckel’s cave. Meckel’s cave is filled with cerebrospinal fluid. The gasserian ganglion lies on the trigeminal impression of the petrous apex. (GG, gasserian ganglion; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 8.16 Exposure of nerves lying in the lateral wall of the cavernous sinus.After removal of the dura propria, all nerves lying on the lateral wall of the cavernous sinus and the internal carotid artery can be seen. (C2, C2 portion of the internal carotid artery), (C4, C4 portion of the internal carotid artery), (C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; II, optic nerve; III, oculo-motor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.17 (Step 5) Opening of Parkinson’s triangle.The meningohypophyseal trunk, the abducens nerve, and Grüber’s ligament (petrosphenoidal ligament) can be seen through Parkinson’s triangle. This exposure can also be achieved by working between the trochlear and the oculomotor nerve and the paramedian triangle. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve ; VI, abducens nerve)Fig. 8.18 Meningohypophyseal trunk.Branching of the meningohypophyseal trunk is visible. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; III, oculomotor nerve; IPS, inferior petrosal sinus; IV, trochlear nerve; MHT, meningohypophyseal trunk; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; VI, abducens nerve)Fig. 8.19 (Step 6) Abducens nerve passing under the petrosphenoidal (Grüber’s) ligament.The abducens nerve passes under the petrosphenoidal (Grüber’s) ligament. This marks the exit of the abducens nerve from the intradural sleeve (Dorello’s canal) through which the nerve passes. The nerve is covered with a venous plexus as it travels through this canal. (C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; IPS, inferior petrosal sinus; PA, petrosal apex; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; VI, abducens nerve)Fig. 8.20 Identifying the petroclinoidal fold.The petroclinoidal fold passes from the petrous tip to the posterior clinoid. The oculomotor nerve passes over the fold of the dura to enter the oculomotor canal. (C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; IPS, inferior petrosal sinus; PA, petrosal apex; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; VI, abducens nerve)Fig. 8.21 C4 portion of the internal carotid artery.The C4 carotid artery is seen between the trochlear nerve and V1. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 8.22 Complete exposure of the cavernous sinus from a lateral direction.Exposure of the cranial nerves in their respective sheaths is technically not difficult. Bleeding from the cavernous sinus or the venous confluence at the petrous tip can be controlled by packing the venous channels with small pieces of oxidized cellulose, and applying gentle pressure and patience. (C2, C2 portion of the internal carotid artery; C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PCP, posterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.23 Removal of the lateral wall of the cavernous sinus.The blue silicone fills the rich venous plexus that surrounds the carotid artery, communicates with the pterygoid plexus over the trigeminal nerve, and passes posterior to the dorsum sellae and the clivus. (GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.24 View after removal of the blue silicone (venous space).A relationship of the nerves and the arteries is demonstrated. At the time of surgery dissection through the venous plexus is not insurmountable. Packing the bleeding points with small pieces of oxidized cellulose and suctioning through a cotton sponge will usually control the venous hemorrhage. (C2, C2 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DR, distal dural ring; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 8.25 Abducens nerve.The abducens nerve is well seen medial to the first division of the trigeminal nerve (V1) through Parkinson’s triangle (lateral triangle). (BA, basilar artery; C2, C2 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DR, distal dural ring; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus; V1, ophthalmic nerve [first division of the trigeminal nerve]; V3, mandibular nerve ; VI, abducens nerve)Fig. 8.26 View after the removal of the trigeminal nerve.Removal of the trigeminal nerve demonstrates not only the abducens nerve but also the C5 portion of the internal carotid artery. This segment lies under the junction of V2, V3, and the gasserian ganglia. (BA, basilar artery; C2, C2 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; COM, carotico-oculomotor membrane; DR, distal dural ring; III, oculomotor nerve; IV, trochlear nerve; PA, petrosal apex; PCA, posterior cerebral artery; PSL, petrosphenoidal ligament; PV, petrosal vein; SCA, superior cerebellar artery; SPS, superior petrosal sinus; VI, abducens nerve)Fig. 8.27 Dorello’s canal.The abducens nerve travels through Dorello’s canal, which is formed by the pyramidal apex and the petrosphenoidal ligant (Grüber’s ligament) and sphenoid bone. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; PA, petrosal apex; PCA, posterior cerebral artery; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SpP, sympathetic plexus; VI, abducens nerve)Fig. 8.28 Internal carotid artery.The wall of the carotid artery is removed, leaving behind the red latex that filled the carotid lumen. (BA, basilar artery; C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PA, petrosal apex; PCA, posterior cerebral artery; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SpP, sympathetic plexus; SPS, superior petrosal sinus; VI, abducens nerve)Fig. 8.29 Anatomy of the paraclinoid and cavernous portion of the internal carotid artery.The carotid artery is seen traveling from the subarachnoid space into the clinoid space between the inner and outer carotid rings. Proximal to the carotid space, the carotid artery enters the cavernous sinus. It exits from the cavernous sinus at the level of the petrolingual ligament, where it is frequently ensheathed in veins well into the petrous canal. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; PA, petrosal apex; PLL, petrolingual ligament; PSL, petrosphenoidal ligament; SpP, sympathetic plexus; VI, abducens nerve)Fig. 8.30 Exposure of the horizontal C6 portion of the internal carotid artery.The C6 portion of the carotid artery is found by drilling the petrous tip under the greater superficial petrosal nerve. Lateral to the carotid canal lies the eustachian tube and the tensor tympani muscle. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; GSPN, greater superior petrosal nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PLL, petrolingual ligament; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus; TFR, trigeminal fibrous ring; TI, trigeminal impression; VI, abducens nerve)Fig. 8.31 Exposure after removal of the internal carotid artery and the nerves.The anatomical relationship between the underlying bones and ligaments is demonstrated. (II, optic nerve; III, oculomotor nerve; MMA, middle meningeal artery; PA, petrosal apex; PCL, petroclival ligament; PCP, posterior clinoid process; PLL, petrolingual ligament; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus)Fig. 8.32 The petrosphenoidal ligament and the petroclival dural fold.The petrous ridge is exposed after the tentorium is removed. (BA, basilar artery; II, optic nerve; III, oculomotor nerve; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PA, petrosal apex; PCA, posterior cerebral artery; PCL, petroclival ligament; PCP, posterior clinoid process; PLL, petrolingual ligament; PICA, posterior inferior cerebellar artery; Po, pons; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus)Fig. 8.33 Magnified view of Fig. 8.32.An anatomical relationship of the petrosphenoidal ligament, petroclinoidal fold and the inferior petrosal sinus is demonstrated. (BA, basilar artery; IPS, inferior petrosal sinus; PA, petrosal apex; PCL, petroclival ligament; PCP, posterior clinoid process; PICA, posterior inferior cerebellar artery; PSL, petrosphenoidal ligament)Fig. 8.34 View after the removal of the dura of the middle cranial base and the clivus.The boney anatomy underlying the structures of the medial middle fossa is seen. (BA, basilar artery; III, oculomotor nerve; PA, petrosal apex; PCA, posterior cerebral artery; PCP, posterior clinoid process; SCA, superior cerebellar artery)Fig. 8.35 Cavernous sinus triangles (see Figs. 8.9 and 8.36).Fig. 8.36 Cavernous sinus triangles(1, Anteromedial triangle [Dolenc]; 2, Medial triangle [Dolenc, Hakuba]; 3, Superior triangle [Fukushima]; 4, Lateral triangle [Parkinson]; 5, Posterolateral triangle [Glasscock, Paullus]; 6, Posteromedial triangle [Kanzaki, Kawase]; 7, Posteroinferior triangle [Fukushima]; 8, Premeatal triangle [Day, Fukushima]; 9, Postmeatal triangle [Day, Fukushima]; 10, Anterolateral triangle [Mullan]; 11, Far lateral triangle [Lateral Loop] [Dolenc]; AE, arcuate eminence; Co, cochlea; IAC, internal auditory canal)
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9 Frontotemporal Orbitozygomatic Transcavernous Approach
3 Transfacial Transmaxillary Approach
7 Orbital Approach
15 Combined Petrosal Approach
12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)
11 Preauricular Transzygomatic Approach to the Anterior Infratemporal Fossa and Middle Infratemporal Fossa
