The Extradural Subtemporal Keyhole Approach to the Sphenocavernous Region: Anatomic Considerations

Abstract

Fourteen cadaver specimens (28 sides) and twelve dry human skulls (24 sides) were used to study the anatomic relationships between bony, neurovascular and foraminal landmarks in the floor of the middle fossa in preparation for performing the extradural subtemporal keyhole approach to the sphenocavernous region. The interforaminal distance was largest between the foramina rotundum (FR) and ovale (FO) and was smallest between the FO and foramen spinosum (FS). The largest angle between exit foramen was the FR to FO. The greater superficial petrosal nerve (GSPN) was always found to overlie and run parallel to the petrous internal carotid artery, however, its location over the artery and its separation from it by bone was variable. With a subtemporal “keyhole” placed above the posterior zygomatic root (PZR), a 0° endoscope allowed easy visualization of the middle meningeal artery (MMA) and the mandibular nerve (V₃) however, a 30° endoscope was more useful for visualizing the maxillary nerve (V₂) and the ophthalmic nerve (V₂). With a sphenoidotomy performed between V₁ and V₂, the 30° endoscope was found to be the most useful for visualizing the carotid siphon and the contralateral wall of the sphenoid sinus, while the 70° endoscope was the most useful for visualizing of the floor of the sella and the walls of the sphenoid sinus. Two venous concerns with respect to performing endoscopic approaches to the region were identified: a fibrous layer overlies a heavy venous plexus that encircles the petrous carotid artery, and the foramen Vesalius, which transmits a large emissary vein draining the cavernous sinus, was identified medial to the FO in 30 % of our dissected sides.

Key words

Middle fossa - microsurgical anatomy - sphenocavernous region - subtemporal keyhole - endoscope

References

• 1 Ginsberg L E, Pruett S W, Chen M YM, Elster A D. Skull-base foramina of the middle cranial fossa: Reassessment of normal variation with high-resolution CT.  AJNR. 1994;  15 283-291
• 2 Inoue T, Rhoton Jr A, Theele D, Barry M. Surgical approaches to the cavernous sinus: A microsurgical study.  Neurosurgery. 1990;  26 903-932
• 3 Klun B, Prestor B. Microvascular relations of the trigeminal nerve: An anatomical study.  Neurosurgery. 1986;  19 535-539
• 4 Tedeschi H, Rhoton Jr A. Lateral approaches to the petroclival region.  Surg Neurol. 1994;  41 180-216
• 5 Krisht A, Barnett D W, Barrow D L, Bonner G. The blood supply of the intracavernous cranial nerves: An anatomic study.  Neurosurgery. 1994;  34 275-279
• 6 Berlis A, Putz R, Schumacher M. Direct and CT measurements of canals and foramina of the skull base.  BJR. 1992;  65 653-661
• 7 Spencer W R, Das K, Nwagu C, Wenk E, Schaefer S, Moscatello A, Couldwell W T. Approaches to the sellar and parasellar region: Anatomic comparison of the microscope versus endoscope.  Laryngoscope. 1999;  109 791-794
• 8 Taniguchi M, Perneczky A. Subtemporal keyhole approach to the suprasellar and petroclival region: Microanatomic considerations and clinical applications.  Neurosurgery. 1997;  41 592-601
• 9 Dew L A, Shelton C, Hamsberger R, Thompson Jr G. Surgical exposure of the petrous internal carotid artery: Practical application for skull base surgery.  Laryngoscope. 1997;  107 967-976
• 10 Naguib M B, Aristegui M, Saleh E. et al . Surgical anatomy of the petrous apex as it relates to the enlarged middle cranial fossa approaches.  Otolaryngol Head Neck Surg. 1994;  111 488-493
• 11 Paullus W, Pait G, Rhoton Jr A. Microsurgical exposure of the petrous portion of the carotid artery.  J Neurosurg. 1977;  47 713-726
• 12 Lang J. Clinical anatomy of the head, neurocranium, orbit and craniocervical regions. New York: Springer-Verlag 1983
• 13 Fukushima T. Endoscopy of Meckel's cave, cisterna magna and cerebellopontine angle.  J Neurosurg. 1978;  48 302-306