J Neurosurg 74:837-844, 1991
The Dolenc technique for cavernous sinus exploration
(cadaveric prosection) Technical note HARRY R. VAN LOVEREN, M.D., JEFFREY T. KELLER, Ptt.D., MAGDY EL-KALLINY, M.D., DANIEl. J. SCODARY,M.D., AND JOHN M. TEW, JR., M.D.
Department of Neurosurgery, Universityof Cincinnati College of Medicine, MayfieldNeurological Institute, and Department of Neurosurgery, The Christ Hospital, Cincinnati, Ohio ~" This report describes a surgical approach to the cavernous sinus. Based on the work of Parkinson, Dolenc, and other pioneering investigators, a comprehensive surgical approach for the treatment of lesions of the cavernous sinus is distilled and presented in 12 simple steps. The approach to surgical exploration of this region is divided into an extradural and intradural phase, each with six steps. The bony, neural, and/or vascular structures of each step are discussed. These steps may be used in their entirety for total exploration of the cavernous sinus, but also in part for lesions that involve only limited regions of the cavernous sinus. Either by design or circumstance, every intracranial neurosurgeon will eventually be led to the cavernous sinus region, and a clear understanding of cavernous sinus anatomy should be part of their armamentarium. KEY WORDS anatomy
9
cavernous sinus
9
HE Intricate " and compact neurovascular contents. J0 of the cavernous sinus led Dwight Parkmson to describe it as the anatomical jewel box (Fig. 1). Because of this complexity, few have dared to approach this region surgically. The perception of an ominous rate of surgical morbidity and mortality resulted in situations in which even benign lesions ran a malignant course. Classic anatomy texts have not provided the essential anatomical detail in a manner suitable for surgical exploration. The first report of successful intracavernous surgery was that of Browder.~ A carotid-cavernous fistula was reported cured by packing muscle through an incision in the roof of the cavernous sinus. However, it was not until the work of Parkinson and R a m s a f 3 that the "inoperability" of the cavernous sinus was seriously challenged. They described an approach into the posterior cavernous sinus through a triangle which now bears Parkinson's name, bordered by the oculomotor and trochlear nerves superiorly and the trigeminal and abducens nerves inferiorly. The inherent risks of circulatory arrest and the method used to achieve vascular control in these procedures dissuaded others from adopting this technique. More recently, drawing upon
cranial nerve
9 skull base
9 surgical approach
9
/
J. Neurosurg. / Voh~me 74/May, 1991
FJG. 1. Artist's enhancement of Dr. Oscar Batson's original cast of the cavernous sinus made at the University of Cincinnati in the 1920's. 837
H. R. van Loveren, et al.
FIG. 3. Superior view of the skull base depicting areas o1 bone to be removed at the extradural phase, la = posterior two-thirds of the orbital floor; lb = roof of the optic canal; 2 = anterior clinoid process; 3 = lateral bony wall of the superior orbital fissure; 4 = bony rim of the foramen rotundum; 5 = bony rim of the foramen ovale; 6 = bone of Glasscock's triangle overlying the horizontal portion of the petrous carotid artery.
FIG. 2. Upper: Patient positioning for cavernous sinus surgery. The patient is in a supine position, thorax elevaled 15~ neck extended, and head rotated 30 ~ from midline. Lower: Drawing of the frontotemporal craniotomy with a three-limb dural incision: Limb I is in line with the sylvian fissure; Limb 2 is perpendicular to the optic nerve; and Limb 3 is parallel to the middle fossa dura. S.O.F. = superior orbital fissure; II1 = the third cranial nerve.
series of 12 simple steps in order to promote the practical application of this information. These steps may be used in whole for total exploration o f the cavernous sinus, but also in part for lesions that involve only limited regions of the cavernous sinus. Operative Procedure
Surgical Positioning existing knowledge as well as extensive personal research, Dolenc 2 reported a method of cavernous sinus exploration without the need for circulatory arrest. Utilizing the work of Parkinson, ~~ Dolenc, 2'3 and other pioneering investigators, we have developed a comprehensive surgical approach for the treatment of lesions of the cavernous sinus. This report attempts to distill the seemingly complex Dolenc technique into a
The outcome o f any surgical procedure will be influenced by appropriate patient positioning. Cavernous sinus exploration is performed with the patient in a supine position, neck extended, and head rotated 30 ~ from midline. Adjustments in head rotation will be necessary during the procedure. A frontotemporal craniotomy is employed which extends anteriorly along the superior orbital rim to the midpoint of the orbit and inferiorly to the zygoma (Fig. 2).
Surgical Approach TABLE 1
Stepsfi)r explorationof the cavernous sinus l a: 2: 3: 4: 5: 6: 838
Extradural Stage orbitalroof; l b: optic canal anteriorclinoid process superiororbital fissure foramenrotundum foramenovale Glasscock'striangle
1: 2: 3: 4: 5: 6:
Intradural Stage duralopening carotidrings oculomotornerve trochlearnerve trigeminalnerve abducensnerve
The approach to surgical exploration of the cavernous sinus is divided into an extradural and intradural phase (Table 1). Each phase comprises six individual steps. All extradural steps involve removal of bone from the anterior and middle cranial fossae. These areas of bone confine portions of the cavernous sinus, as well as the orbit, superior orbital fissure, Meckel's cave, and petrous carotid artery. The removal o f these bony areas is the key to unlocking the neurovascular structures for intradural exploration (Fig. 3). The intradural steps
J. Neurosurg. / Volume 74 / May, 1991
Cavernous sinus exploration
FIG. 4. Extradural Steps 1 and 2. In Step I, starting from the inferior half of the "keyhole," the posterior two-thirds of the orbital roof is removed, followedby unroofing of the optic canal. Step 2 involvesextradural removal of the anterior clinoid process. S.O.K = superior orbital fissure; ICA = internal carotid artery.
essentially unlock the neurovascular structures from dural confinement while allowing the surgeon to remain extracavernous. Application of this approach facilitates control of the arterial and venous circulation, obviating the need for circulatory arrest.
Extradural Stage Step la: Orbital Roof The dura is separated from the floor of the anterior cranial fossa. The posterior two-thirds of the orbital roof is removed with a highspeed drill* and conventional rongeurs. The medial portion of the orbital roof which slopes downward towards the cribriform plate is preserved to avoid entry into ethmoid and sphenoid air cells (Fig. 4). Step Ib: Optic Canal. The bony roof of the optic canal is removed with a diamond burr. This permits mobilization of the optic nerve which is essential to avoid optic nerve injury during subsequent dissection of the anterior clinoid process (Fig. 4). Step 2: Anterior Clinoid Process. With a diamond burr, the anterior clinoid process is cored leaving a thin shell of cortical bone which can be fractured in upon itself. This will also expose the bony strut beneath the optic nerve. Removal of the medial sphenoid wing and * High-speed drill manufactured by Midas Rex Pneumatic Tools Inc., Fort Worth, Texas.
J. Neurosurg. / Volume 74/May, 1991
bony strut disconnects the anterior clinoid process from the skull base (Fig. 4). The anterior clinoid process lies within the anteromedial triangle bordered by the optic nerve medially and oculomotor nerve laterally. The anterior loop of the carotid artery lies within the floor of this triangle. This is the clinoid segment of the internal carotid artery (ICA) which is neither intracavernous nor intradural. The majority of carotid-ophthalmic aneurysms which appear to have an intracavernous component actually arise from the clinoid segment of the ICA and violate the distal dural ring. Step 3: Superior Orbital Fissure. Removal of the medial sphenoid wing will have revealed the dura overlying the superior orbital fissure. The lateral bony wall of the superior orbital fissure is thinned, fractured, and removed (Fig. 5). Step 4: Foramen Rotundurn. A small island of bone separates the inferior aspect of the superior orbital fissure from the foramen rotundum. The anterolateral rim of the foramen is removed with a diamond burr permitting mobilization of the maxillary division of the trigeminal nerve (Fig. 5). Step 5: Foramen Ovale. Elevation of the middle fossa dura is continued to the vertical inclination of the petrous pyramid, revealing both the foramen ovale and 839
H. R. v a n L o v e r e n , et al. foramen spinosum. The middle meningeal artery traversing the foramen spinosum is sacrificed. The anterolateral boundaries of the foramen ovale are expanded enabling mobilization of the mandibular nerve (Fig. 6). Step 6." Glasscock's Triangle. Glasscock's triangle, 4,5 or the posterolateral triangle, is bordered laterally by a line between the foramen spinosum and the arcuate eminence and medially by the groove of the greater superficial petrosal nerve; it has as its base the dorsal aspect of the third division of the trigeminal nerve. The greater superficial petrosal nerve is sacrificed to avoid traction injury to the geniculate ganglion and facial nerve. The bone of Glasscock's triangle is removed with a diamond burr exposing the lateral loop of the ICA within the petrous bone. Unroofing of the petrous bone over the ICA should not proceed posteriorly beyond the point where the ICA turns vertically if injury to the cochlea is to be avoided. Exposure of the petrous ICA permits proximal arterial control and offers a potential site for bypass vascular grafting (Fig. 6).
Intradural Stage Step 1: Dural Opening. The dural opening begins along the line of the sylvian fissure. The incision is extended medially, perpendicular to the optic nerve, and laterally across the temporal lobe (Fig. 2 lower).
Step 2: Carotid Rings. The ICA is fixed by two dural rings: the proximal ring is the exit point of the ICA from the cavernous sinus and the distal ring is the point where the ICA becomes intradural. The clinoid segment of the ICA lies between these two rings. These tings are sectioned allowing mobilization of the clinoid segment and entry into the anterior cavernous sinus (Fig. 7). Step 3." Oculomotor Nerve. The oculomotor nerve is identified as it enters the edge of the tentorial dura lateral to the posterior clinoid process. The dura overlying the third nerve is incised using an arachnoid knife. This incision is carried rostrally to the point at which the third nerve crosses the ICA (anterior loop) (Fig. 8). This avoids injury to the trochlear nerve which crosses over the oculomotor nerve in the superior orbital fissure. The deep membranous layer of the lateral wall of the cavernous sinus separates these nerves from the venous channels of the cavernous sinus. Step 4: Troehlear Nerve. The troehlear nerve is identified as it enters the edge of the tentorial dura posterolateral to the oeulomotor nerve. Dissection of dura overlying the fourth nerve is continued anteriorly into the superior orbital fissure (Fig. 8). Step 5. Trigeminal Nerve. The ophthalmic division of the trigeminal nerve is identified rostrally near the
FIG. 5. Extradural Steps 3 and 4. Step 3 involves fracture and removal of the lateral bony wall of the superior orbital fissure (S.O.F.). Step 4 comprises removal of the bony tim of the foramen rotundum. V2 = the second division of the trigeminal nerve. 840
J. Neurosurg. / Volume 74/May, 1991
FIG. 6. Extradural Steps 5 and 6. In Step 5, after the middle meningeal artery (MMA) is sacrificed, the bony rim of the foramen ovale is drilled and widened. In Step 6, the horizontal petrous carotid artery is exposed by drilling the bone of Glasscock's triangle. Immediately lateral to the petrous carotid artery lies the tensor tympani muscle and deep to this muscle is the eustachian tube. GPN = greater superficial petrosal nerve; ICA = internal carotid artery; S.O.F. = superior orbital fissure; V2 and V3 = second and third divisions of the trigeminal nerve.
FIG. 7. Intradural Steps 1 and 2. In Step 1, a three-limb dural incision is made as depicted in Fig. 2 lower. Step 2 involves sectioning the carotid rings. The internal carotid artery (ICA) leaves the cavernous sinus at the proximal carotid ring and becomes intradural at the distal dural ring. The clinoid segment of the ICA is visualized between the proximal and distal dural rings. S.O.F. = superior orbital fissure; P.C. = posterior clinoid process; roman numerals denote cranial nerves.
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H. R. van Loveren, et al.
FIG. 8. Intradural Steps 3 to 5. The lateral dural wall of the cavernous sinus and Meckel's cave is dissected from the underlying cranial nerves. Cranial nerves III, IV, and VI merge as they enter the superior orbital fissure. P.C. = posterior clinoid process; ICA = internal carotid artery; roman numerals denote cranial nerves.
FIG. 9. Intradural Steps 5 and 6, involving complete exposure of the cavernous sinus and Meckel's cave. The abducens nerve (VI) can be identified by retraction of the ophthalmic division of the trigeminal nerve (VI). This is the only intracavernous cranial nerve. Roman numerals denote cranial nerves; ICA = internal carotid artery. 842
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Cavernous sinus exNoration
FIG. 10. Nine triangles of the cavernous sinus region. I = Anteromedial triangle: medial, optic nerve; lateral, oculomotor nerve: base, dural edge. 2 = Paramedial triangle: medial, third nerve: lateral, trochlear nerve; base, dural edge of tentorium. 3 = Parkinson's triangle: medial trochlear nerve: lateral, first division of the trigeminal nerve (V~); base, dural edge of tentorium. 4 = Anterolateral triangle: medial, V~ trigeminal nerve; lateral, second division of the trigeminal nerve (V2); base, line between V~ in the superior orbital fissure and the foramen ovale. 5 = Lateral triangle: medial, Vz trigeminal nerve~ lateral, third division of the trigeminal nerve (V3): base, line between the foramen rotundum and the foramen ovale. 6 = Posterolateral (Glasscock's) triangle: lateral, line between the foramen spinosum and the arcuate eminence; medial, greater superficial petrosal nerve: base, dorsal aspect of V3 trigeminal nerve. 7 = Posteromedial (Kawase's) triangle: lateral, greater superficial petrosal nerve: medial, petrosal sinus: base, trigeminal nerve. 8 = Inferomedial triangle: posterior view: medial, line between the posterior clinoid and the abducens nerve (VI) at Dorello's canal; lateral, line between Dorello's canal and the trochlear nerve (IV) at the edge of the tentorium; base, petrous apex. 9 = Inferolateral triangle; posterior view: medial, line between Dorello's canal and trochlear nerve at the edge of the tentorium; lateral, line between Dorello's canal and the petrosal vein at the petrosal sinus; base, petrous apex. Roman numerals denote cranial nerves.
superior orbital fissure and its dural covering is dissected (Fig. 8). This dissection is carried posteriorly toward Meckel's cave. At this stage the lateral wall of the cavernous sinus is totally exposed, and the sinus may be entered. Meckel's cave may be exposed by further dissection of dura from the trigeminal ganglion and its second and third divisions. The trigeminal ganglion is separated from the ICA by the bony floor of Meckel's cave which may be incompetent (Fig. 9).
Parkinson and Ramsay j3 by describing the cavernous sinus region as a series of nine triangles. The compartmentalization of this complex anatomy aids in understanding the neurovascular relationships within the cavernous sinus region (see Fig. 10 for a description of the cavernous sinus triangles).
Step 6. Abducens Nerve. The abducens nerve enters the cavernous sinus via Dorello's canal. This nerve, which may be duplicate or even triplicate, lies lateral to the ICA. The abducens nerve is the only cranial nerve truly within the cavernous sinus. The meningohypophyseal artery can be identified at the junction of the abducens nerve and the ICA (Fig. 9).
course from the petrous bone to the intradural space
Triangles of the Cavernous Sinus Region Dolenc ~3 has expanded upon the original work of
J. Neurosurg. / Volume 74~May, 1991
Internal Carotid Artery The ICA changes direction through four loops in its (Fig. 11). The first loop (posterior loop or geniculum) marks the transition of the petrous carotid artery from a vertical to a horizontal position in the petrous bone. The horizontal portion of the petrous carotid artery runs anteromedial under the trigeminal ganglion, crossing the foramen lacerum and forming the lateral loop. The carotid artery then ascends into the posterior aspect of the cavernous sinus where the medial loop is formed lateral to the posterior clinoid process as the carotid
843
H . R. v a n L o v e r e n , et al. malignant problem for the patient. The primary tenet of skull base surgery is that accessibility should not determine the resectability of an otherwise benign tumor. New corridors to tumors of the skull base are being developed by a return to the traditional role of neurosurgeon as neuroanatomist. In this particular case, Parkinson ~~described the cavernous sinus as an "anatomical jewel box," and understanding the anatomy as presented in these 12 steps is the key that unlocks it. Either by design or circumstance, every intracranial neurosurgeon will eventually be led to the cavernous sinus region and a clear understanding of cavernous sinus anatomy should be part of their armamentarium. Future anatomical investigation should be directed at the vascular supply of cavernous cranial nerves which are likely to be the most critical factor in preserving neural function during surgery in this region. FIG. 11. Loops of the internal carotid artery (ICA). The posterior loop marks the transition between the vertical and horizontal petrous carotid artery, The lateral loop courses deep to the trigeminal ganglion toward the foramen lacerum. The medial loop is nearly vertical and marks the transition between the vertical and horizontal cavernous carotid artery. The anterior loop is nearly horizontal and brings the ICA from the cavernous sinus through the clinoid segment into the intradural compartment.
artery courses anteriorly. The anterior (fourth) loop in the anterior cavernous sinus is nearly horizontal and brings the ICA from the cavernous sinus through its clinoid segment and into the intradural space (Fig. 11). Comment Intracavernous collateral vessels of the ICA have been recognized since 1860, when Luschka described the posteroinferior hypophyseal artery. 7 More recently, Parkinson and Ramsey, ~-~3 Harris and Rhoton, 6 and Lasjaunias, et al., 8 have described the major branches of the intracavernous carotid artery: meningohypophyseal trunk, inferolateral trunk or inferior artery of the cavernous sinus, and McConnel's capsular artery. The reader is referred to the work of Lasjaunias 9 for a comprehensive discussion of the anatomical and neuroradiological features of intracavernous carotid branches. This work is of particular value since consideration of the vascular supply of the third through sixth cranial nerves associated with the cavernous sinus as well as collateral blood supply to this region are presented in exquisite detail. The complex neurovascular, bony, and muscular anatomy of the skull base have dissuaded neurosurgeons from operating in this region for many decades. Because of this, tumors of the skull base which are histologically benign have been allowed to become a
844
References 1. Browder J: Treatment of carotid artery cavernous sinus fistula. Report of a case. Arch Ophthalmol 18:95-102, 1937 2. Dolenc V: Direct microsurgical repair of intracavernous vascular lesions. J Neurosurg 58:824-831, 1983 3. Dolcnc VV (ed): The Cavernous Sinus. New York: Springer-Verlag, 1987 4. Glasscock ME III, Miller GW, Drake FD, et al: Surgery of the skull base. Laryngoscope 88:905-923, 1978 5. Glasscock ME Ill, Smith PG, Bond AG, et al: Management of aneurysms of the petrous portion of the internal carotid artery by resection and primary anastomosis. Laryngoscope 93:1445-1453, 1983 6. Harris FS, Rhoton AL Jr: Anatomy of the cavernous sinus. A microsurgical study. J Neurosurg 45:169-180, 1976 7. Lapresle J, Lasjaunias P: Cranial nerve ischemic arterial syndromes. Brain 109:207-215, 1986 8. Lasjaunias P, Morel J, Mink J: The anatomy of the inferolateral trunk (ILT) of the internal carotid artery. Neuroradiology 13:215-220, 1977 9. Lasjaunias PL: Craniofacial and Upper Cervical Arteries: Functional, Clinical and Angiographic Aspects. Baltimore: Williams & Wilkins, 1981 10. Parkinson D: Carotid cavernous fistula. History and anatomy, in Dolenc VV (ed): The Cavernous Sinus. New York: Springer-Verlag, 1987, pp 3-29 11. Parkinson D: Collateral circulation of cavernous carotid artery: anatomy. Can J Surg 7:251-268, 1964 12. Parkinson D: A surgical approach to the cavernous portion of the carotid artery. Anatomical studies and case report. J Nenrosurg 23:474-483, 1965 13. Parkinson D, Ramsay RM: Carotid cavernous fistula with pulsating exophthalmos: a fortuitous cure. Can J Surg 6: 191-195, 1963 Manuscript received April 17, 1990. Accepted in final form September 21, 1990. Address reprint requests to: Harry R. van Loveren, M.D., Department of Neurosurgery, University of Cincinnati College of Medicine, 231 Bethesda Avenue, Cincinnati, Ohio 45267-0515.
J. Neurosurg. / Volume 74~May, 1991
The Dolenc technique for cavernous sinus exploration
(cadaveric prosection) Technical note HARRY R. VAN LOVEREN, M.D., JEFFREY T. KELLER, Ptt.D., MAGDY EL-KALLINY, M.D., DANIEl. J. SCODARY,M.D., AND JOHN M. TEW, JR., M.D.
Department of Neurosurgery, Universityof Cincinnati College of Medicine, MayfieldNeurological Institute, and Department of Neurosurgery, The Christ Hospital, Cincinnati, Ohio ~" This report describes a surgical approach to the cavernous sinus. Based on the work of Parkinson, Dolenc, and other pioneering investigators, a comprehensive surgical approach for the treatment of lesions of the cavernous sinus is distilled and presented in 12 simple steps. The approach to surgical exploration of this region is divided into an extradural and intradural phase, each with six steps. The bony, neural, and/or vascular structures of each step are discussed. These steps may be used in their entirety for total exploration of the cavernous sinus, but also in part for lesions that involve only limited regions of the cavernous sinus. Either by design or circumstance, every intracranial neurosurgeon will eventually be led to the cavernous sinus region, and a clear understanding of cavernous sinus anatomy should be part of their armamentarium. KEY WORDS anatomy
9
cavernous sinus
9
HE Intricate " and compact neurovascular contents. J0 of the cavernous sinus led Dwight Parkmson to describe it as the anatomical jewel box (Fig. 1). Because of this complexity, few have dared to approach this region surgically. The perception of an ominous rate of surgical morbidity and mortality resulted in situations in which even benign lesions ran a malignant course. Classic anatomy texts have not provided the essential anatomical detail in a manner suitable for surgical exploration. The first report of successful intracavernous surgery was that of Browder.~ A carotid-cavernous fistula was reported cured by packing muscle through an incision in the roof of the cavernous sinus. However, it was not until the work of Parkinson and R a m s a f 3 that the "inoperability" of the cavernous sinus was seriously challenged. They described an approach into the posterior cavernous sinus through a triangle which now bears Parkinson's name, bordered by the oculomotor and trochlear nerves superiorly and the trigeminal and abducens nerves inferiorly. The inherent risks of circulatory arrest and the method used to achieve vascular control in these procedures dissuaded others from adopting this technique. More recently, drawing upon
cranial nerve
9 skull base
9 surgical approach
9
/
J. Neurosurg. / Voh~me 74/May, 1991
FJG. 1. Artist's enhancement of Dr. Oscar Batson's original cast of the cavernous sinus made at the University of Cincinnati in the 1920's. 837
H. R. van Loveren, et al.
FIG. 3. Superior view of the skull base depicting areas o1 bone to be removed at the extradural phase, la = posterior two-thirds of the orbital floor; lb = roof of the optic canal; 2 = anterior clinoid process; 3 = lateral bony wall of the superior orbital fissure; 4 = bony rim of the foramen rotundum; 5 = bony rim of the foramen ovale; 6 = bone of Glasscock's triangle overlying the horizontal portion of the petrous carotid artery.
FIG. 2. Upper: Patient positioning for cavernous sinus surgery. The patient is in a supine position, thorax elevaled 15~ neck extended, and head rotated 30 ~ from midline. Lower: Drawing of the frontotemporal craniotomy with a three-limb dural incision: Limb I is in line with the sylvian fissure; Limb 2 is perpendicular to the optic nerve; and Limb 3 is parallel to the middle fossa dura. S.O.F. = superior orbital fissure; II1 = the third cranial nerve.
series of 12 simple steps in order to promote the practical application of this information. These steps may be used in whole for total exploration o f the cavernous sinus, but also in part for lesions that involve only limited regions of the cavernous sinus. Operative Procedure
Surgical Positioning existing knowledge as well as extensive personal research, Dolenc 2 reported a method of cavernous sinus exploration without the need for circulatory arrest. Utilizing the work of Parkinson, ~~ Dolenc, 2'3 and other pioneering investigators, we have developed a comprehensive surgical approach for the treatment of lesions of the cavernous sinus. This report attempts to distill the seemingly complex Dolenc technique into a
The outcome o f any surgical procedure will be influenced by appropriate patient positioning. Cavernous sinus exploration is performed with the patient in a supine position, neck extended, and head rotated 30 ~ from midline. Adjustments in head rotation will be necessary during the procedure. A frontotemporal craniotomy is employed which extends anteriorly along the superior orbital rim to the midpoint of the orbit and inferiorly to the zygoma (Fig. 2).
Surgical Approach TABLE 1
Stepsfi)r explorationof the cavernous sinus l a: 2: 3: 4: 5: 6: 838
Extradural Stage orbitalroof; l b: optic canal anteriorclinoid process superiororbital fissure foramenrotundum foramenovale Glasscock'striangle
1: 2: 3: 4: 5: 6:
Intradural Stage duralopening carotidrings oculomotornerve trochlearnerve trigeminalnerve abducensnerve
The approach to surgical exploration of the cavernous sinus is divided into an extradural and intradural phase (Table 1). Each phase comprises six individual steps. All extradural steps involve removal of bone from the anterior and middle cranial fossae. These areas of bone confine portions of the cavernous sinus, as well as the orbit, superior orbital fissure, Meckel's cave, and petrous carotid artery. The removal o f these bony areas is the key to unlocking the neurovascular structures for intradural exploration (Fig. 3). The intradural steps
J. Neurosurg. / Volume 74 / May, 1991
Cavernous sinus exploration
FIG. 4. Extradural Steps 1 and 2. In Step I, starting from the inferior half of the "keyhole," the posterior two-thirds of the orbital roof is removed, followedby unroofing of the optic canal. Step 2 involvesextradural removal of the anterior clinoid process. S.O.K = superior orbital fissure; ICA = internal carotid artery.
essentially unlock the neurovascular structures from dural confinement while allowing the surgeon to remain extracavernous. Application of this approach facilitates control of the arterial and venous circulation, obviating the need for circulatory arrest.
Extradural Stage Step la: Orbital Roof The dura is separated from the floor of the anterior cranial fossa. The posterior two-thirds of the orbital roof is removed with a highspeed drill* and conventional rongeurs. The medial portion of the orbital roof which slopes downward towards the cribriform plate is preserved to avoid entry into ethmoid and sphenoid air cells (Fig. 4). Step Ib: Optic Canal. The bony roof of the optic canal is removed with a diamond burr. This permits mobilization of the optic nerve which is essential to avoid optic nerve injury during subsequent dissection of the anterior clinoid process (Fig. 4). Step 2: Anterior Clinoid Process. With a diamond burr, the anterior clinoid process is cored leaving a thin shell of cortical bone which can be fractured in upon itself. This will also expose the bony strut beneath the optic nerve. Removal of the medial sphenoid wing and * High-speed drill manufactured by Midas Rex Pneumatic Tools Inc., Fort Worth, Texas.
J. Neurosurg. / Volume 74/May, 1991
bony strut disconnects the anterior clinoid process from the skull base (Fig. 4). The anterior clinoid process lies within the anteromedial triangle bordered by the optic nerve medially and oculomotor nerve laterally. The anterior loop of the carotid artery lies within the floor of this triangle. This is the clinoid segment of the internal carotid artery (ICA) which is neither intracavernous nor intradural. The majority of carotid-ophthalmic aneurysms which appear to have an intracavernous component actually arise from the clinoid segment of the ICA and violate the distal dural ring. Step 3: Superior Orbital Fissure. Removal of the medial sphenoid wing will have revealed the dura overlying the superior orbital fissure. The lateral bony wall of the superior orbital fissure is thinned, fractured, and removed (Fig. 5). Step 4: Foramen Rotundurn. A small island of bone separates the inferior aspect of the superior orbital fissure from the foramen rotundum. The anterolateral rim of the foramen is removed with a diamond burr permitting mobilization of the maxillary division of the trigeminal nerve (Fig. 5). Step 5: Foramen Ovale. Elevation of the middle fossa dura is continued to the vertical inclination of the petrous pyramid, revealing both the foramen ovale and 839
H. R. v a n L o v e r e n , et al. foramen spinosum. The middle meningeal artery traversing the foramen spinosum is sacrificed. The anterolateral boundaries of the foramen ovale are expanded enabling mobilization of the mandibular nerve (Fig. 6). Step 6." Glasscock's Triangle. Glasscock's triangle, 4,5 or the posterolateral triangle, is bordered laterally by a line between the foramen spinosum and the arcuate eminence and medially by the groove of the greater superficial petrosal nerve; it has as its base the dorsal aspect of the third division of the trigeminal nerve. The greater superficial petrosal nerve is sacrificed to avoid traction injury to the geniculate ganglion and facial nerve. The bone of Glasscock's triangle is removed with a diamond burr exposing the lateral loop of the ICA within the petrous bone. Unroofing of the petrous bone over the ICA should not proceed posteriorly beyond the point where the ICA turns vertically if injury to the cochlea is to be avoided. Exposure of the petrous ICA permits proximal arterial control and offers a potential site for bypass vascular grafting (Fig. 6).
Intradural Stage Step 1: Dural Opening. The dural opening begins along the line of the sylvian fissure. The incision is extended medially, perpendicular to the optic nerve, and laterally across the temporal lobe (Fig. 2 lower).
Step 2: Carotid Rings. The ICA is fixed by two dural rings: the proximal ring is the exit point of the ICA from the cavernous sinus and the distal ring is the point where the ICA becomes intradural. The clinoid segment of the ICA lies between these two rings. These tings are sectioned allowing mobilization of the clinoid segment and entry into the anterior cavernous sinus (Fig. 7). Step 3." Oculomotor Nerve. The oculomotor nerve is identified as it enters the edge of the tentorial dura lateral to the posterior clinoid process. The dura overlying the third nerve is incised using an arachnoid knife. This incision is carried rostrally to the point at which the third nerve crosses the ICA (anterior loop) (Fig. 8). This avoids injury to the trochlear nerve which crosses over the oculomotor nerve in the superior orbital fissure. The deep membranous layer of the lateral wall of the cavernous sinus separates these nerves from the venous channels of the cavernous sinus. Step 4: Troehlear Nerve. The troehlear nerve is identified as it enters the edge of the tentorial dura posterolateral to the oeulomotor nerve. Dissection of dura overlying the fourth nerve is continued anteriorly into the superior orbital fissure (Fig. 8). Step 5. Trigeminal Nerve. The ophthalmic division of the trigeminal nerve is identified rostrally near the
FIG. 5. Extradural Steps 3 and 4. Step 3 involves fracture and removal of the lateral bony wall of the superior orbital fissure (S.O.F.). Step 4 comprises removal of the bony tim of the foramen rotundum. V2 = the second division of the trigeminal nerve. 840
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FIG. 6. Extradural Steps 5 and 6. In Step 5, after the middle meningeal artery (MMA) is sacrificed, the bony rim of the foramen ovale is drilled and widened. In Step 6, the horizontal petrous carotid artery is exposed by drilling the bone of Glasscock's triangle. Immediately lateral to the petrous carotid artery lies the tensor tympani muscle and deep to this muscle is the eustachian tube. GPN = greater superficial petrosal nerve; ICA = internal carotid artery; S.O.F. = superior orbital fissure; V2 and V3 = second and third divisions of the trigeminal nerve.
FIG. 7. Intradural Steps 1 and 2. In Step 1, a three-limb dural incision is made as depicted in Fig. 2 lower. Step 2 involves sectioning the carotid rings. The internal carotid artery (ICA) leaves the cavernous sinus at the proximal carotid ring and becomes intradural at the distal dural ring. The clinoid segment of the ICA is visualized between the proximal and distal dural rings. S.O.F. = superior orbital fissure; P.C. = posterior clinoid process; roman numerals denote cranial nerves.
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FIG. 8. Intradural Steps 3 to 5. The lateral dural wall of the cavernous sinus and Meckel's cave is dissected from the underlying cranial nerves. Cranial nerves III, IV, and VI merge as they enter the superior orbital fissure. P.C. = posterior clinoid process; ICA = internal carotid artery; roman numerals denote cranial nerves.
FIG. 9. Intradural Steps 5 and 6, involving complete exposure of the cavernous sinus and Meckel's cave. The abducens nerve (VI) can be identified by retraction of the ophthalmic division of the trigeminal nerve (VI). This is the only intracavernous cranial nerve. Roman numerals denote cranial nerves; ICA = internal carotid artery. 842
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FIG. 10. Nine triangles of the cavernous sinus region. I = Anteromedial triangle: medial, optic nerve; lateral, oculomotor nerve: base, dural edge. 2 = Paramedial triangle: medial, third nerve: lateral, trochlear nerve; base, dural edge of tentorium. 3 = Parkinson's triangle: medial trochlear nerve: lateral, first division of the trigeminal nerve (V~); base, dural edge of tentorium. 4 = Anterolateral triangle: medial, V~ trigeminal nerve; lateral, second division of the trigeminal nerve (V2); base, line between V~ in the superior orbital fissure and the foramen ovale. 5 = Lateral triangle: medial, Vz trigeminal nerve~ lateral, third division of the trigeminal nerve (V3): base, line between the foramen rotundum and the foramen ovale. 6 = Posterolateral (Glasscock's) triangle: lateral, line between the foramen spinosum and the arcuate eminence; medial, greater superficial petrosal nerve: base, dorsal aspect of V3 trigeminal nerve. 7 = Posteromedial (Kawase's) triangle: lateral, greater superficial petrosal nerve: medial, petrosal sinus: base, trigeminal nerve. 8 = Inferomedial triangle: posterior view: medial, line between the posterior clinoid and the abducens nerve (VI) at Dorello's canal; lateral, line between Dorello's canal and the trochlear nerve (IV) at the edge of the tentorium; base, petrous apex. 9 = Inferolateral triangle; posterior view: medial, line between Dorello's canal and trochlear nerve at the edge of the tentorium; lateral, line between Dorello's canal and the petrosal vein at the petrosal sinus; base, petrous apex. Roman numerals denote cranial nerves.
superior orbital fissure and its dural covering is dissected (Fig. 8). This dissection is carried posteriorly toward Meckel's cave. At this stage the lateral wall of the cavernous sinus is totally exposed, and the sinus may be entered. Meckel's cave may be exposed by further dissection of dura from the trigeminal ganglion and its second and third divisions. The trigeminal ganglion is separated from the ICA by the bony floor of Meckel's cave which may be incompetent (Fig. 9).
Parkinson and Ramsay j3 by describing the cavernous sinus region as a series of nine triangles. The compartmentalization of this complex anatomy aids in understanding the neurovascular relationships within the cavernous sinus region (see Fig. 10 for a description of the cavernous sinus triangles).
Step 6. Abducens Nerve. The abducens nerve enters the cavernous sinus via Dorello's canal. This nerve, which may be duplicate or even triplicate, lies lateral to the ICA. The abducens nerve is the only cranial nerve truly within the cavernous sinus. The meningohypophyseal artery can be identified at the junction of the abducens nerve and the ICA (Fig. 9).
course from the petrous bone to the intradural space
Triangles of the Cavernous Sinus Region Dolenc ~3 has expanded upon the original work of
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Internal Carotid Artery The ICA changes direction through four loops in its (Fig. 11). The first loop (posterior loop or geniculum) marks the transition of the petrous carotid artery from a vertical to a horizontal position in the petrous bone. The horizontal portion of the petrous carotid artery runs anteromedial under the trigeminal ganglion, crossing the foramen lacerum and forming the lateral loop. The carotid artery then ascends into the posterior aspect of the cavernous sinus where the medial loop is formed lateral to the posterior clinoid process as the carotid
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H . R. v a n L o v e r e n , et al. malignant problem for the patient. The primary tenet of skull base surgery is that accessibility should not determine the resectability of an otherwise benign tumor. New corridors to tumors of the skull base are being developed by a return to the traditional role of neurosurgeon as neuroanatomist. In this particular case, Parkinson ~~described the cavernous sinus as an "anatomical jewel box," and understanding the anatomy as presented in these 12 steps is the key that unlocks it. Either by design or circumstance, every intracranial neurosurgeon will eventually be led to the cavernous sinus region and a clear understanding of cavernous sinus anatomy should be part of their armamentarium. Future anatomical investigation should be directed at the vascular supply of cavernous cranial nerves which are likely to be the most critical factor in preserving neural function during surgery in this region. FIG. 11. Loops of the internal carotid artery (ICA). The posterior loop marks the transition between the vertical and horizontal petrous carotid artery, The lateral loop courses deep to the trigeminal ganglion toward the foramen lacerum. The medial loop is nearly vertical and marks the transition between the vertical and horizontal cavernous carotid artery. The anterior loop is nearly horizontal and brings the ICA from the cavernous sinus through the clinoid segment into the intradural compartment.
artery courses anteriorly. The anterior (fourth) loop in the anterior cavernous sinus is nearly horizontal and brings the ICA from the cavernous sinus through its clinoid segment and into the intradural space (Fig. 11). Comment Intracavernous collateral vessels of the ICA have been recognized since 1860, when Luschka described the posteroinferior hypophyseal artery. 7 More recently, Parkinson and Ramsey, ~-~3 Harris and Rhoton, 6 and Lasjaunias, et al., 8 have described the major branches of the intracavernous carotid artery: meningohypophyseal trunk, inferolateral trunk or inferior artery of the cavernous sinus, and McConnel's capsular artery. The reader is referred to the work of Lasjaunias 9 for a comprehensive discussion of the anatomical and neuroradiological features of intracavernous carotid branches. This work is of particular value since consideration of the vascular supply of the third through sixth cranial nerves associated with the cavernous sinus as well as collateral blood supply to this region are presented in exquisite detail. The complex neurovascular, bony, and muscular anatomy of the skull base have dissuaded neurosurgeons from operating in this region for many decades. Because of this, tumors of the skull base which are histologically benign have been allowed to become a
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References 1. Browder J: Treatment of carotid artery cavernous sinus fistula. Report of a case. Arch Ophthalmol 18:95-102, 1937 2. Dolenc V: Direct microsurgical repair of intracavernous vascular lesions. J Neurosurg 58:824-831, 1983 3. Dolcnc VV (ed): The Cavernous Sinus. New York: Springer-Verlag, 1987 4. Glasscock ME III, Miller GW, Drake FD, et al: Surgery of the skull base. Laryngoscope 88:905-923, 1978 5. Glasscock ME Ill, Smith PG, Bond AG, et al: Management of aneurysms of the petrous portion of the internal carotid artery by resection and primary anastomosis. Laryngoscope 93:1445-1453, 1983 6. Harris FS, Rhoton AL Jr: Anatomy of the cavernous sinus. A microsurgical study. J Neurosurg 45:169-180, 1976 7. Lapresle J, Lasjaunias P: Cranial nerve ischemic arterial syndromes. Brain 109:207-215, 1986 8. Lasjaunias P, Morel J, Mink J: The anatomy of the inferolateral trunk (ILT) of the internal carotid artery. Neuroradiology 13:215-220, 1977 9. Lasjaunias PL: Craniofacial and Upper Cervical Arteries: Functional, Clinical and Angiographic Aspects. Baltimore: Williams & Wilkins, 1981 10. Parkinson D: Carotid cavernous fistula. History and anatomy, in Dolenc VV (ed): The Cavernous Sinus. New York: Springer-Verlag, 1987, pp 3-29 11. Parkinson D: Collateral circulation of cavernous carotid artery: anatomy. Can J Surg 7:251-268, 1964 12. Parkinson D: A surgical approach to the cavernous portion of the carotid artery. Anatomical studies and case report. J Nenrosurg 23:474-483, 1965 13. Parkinson D, Ramsay RM: Carotid cavernous fistula with pulsating exophthalmos: a fortuitous cure. Can J Surg 6: 191-195, 1963 Manuscript received April 17, 1990. Accepted in final form September 21, 1990. Address reprint requests to: Harry R. van Loveren, M.D., Department of Neurosurgery, University of Cincinnati College of Medicine, 231 Bethesda Avenue, Cincinnati, Ohio 45267-0515.
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