The Petrosal Approach Saleem I. Abdulrauf, MD and Ossama Al-Mefty, MD Traditionally, the approach to the perimescencephalic and petroclival region has been challenging to the neurosurgeon. Approaches to this region have been associated with multiple complications including excessive temporal lobe and cerebellum retraction, hearing loss, facial nerve injury, and venous infarction. The petrosal approach is intended to provide direct access to the petroclival-perimesencephalic region while minimizing the above neuro-otologic complications. The approach relies on a retrolaby- rinthine presigmoid window using a single temporo-suboccipital bone flap combined with a mastoidectomy and tentorial splitting, while preserving the major venous sinuses. Copyright 9 1999 by W.B. Saunders Company T he petrosal approach, also known as the posterior petrosal approach, provides the neurosurgeon with excellent access to the petroclival region, the basilar trunk and apex, the anteromedial midbrain and the pons. To access these regions, the petrosal approach offers a number of advantages: (1) The surgeon's operative distance to these regions is shorter than in the retrosigmoid approaches. (2) There is minimal retraction of the cerebellum and temporal lobe. (3) The neural structures (seventh and eight nerve) are preserved. (4) The otologic structures (cochlea, labyrinth, semicircular canals) are pre- served. (5) Finally, the major venous sinuses (transverse and sigmoid), along with the vein of Labb4 and other temporal and basal veins, are preserved. Historical Perspectives In 1904, Fraenkel and Hunt 1 described a suboccipital craniec- tomy combined with a translabyrinthine approach to acoustic tumors. Marx, 2 in 1913, suggested that combining an opening through the petrous portion of the temporal bone with an opening in the subocciput would create a broader passage through the skull and therefore allow more direct access to the tumor's base. Naffziger,3 in 1928, described the transtentorial approach to tumors of posterior fossa and the cerebellopontine angle (CPA). In 1930, Fay§ described a combined occipitotem- poral and suboccipital flap with or without ligation of the lateral sinus. Bailey, 5 in 1939, described an approach to the CPA through a unilateral osteoplastic flap that incorporated bone over the occipital lobe as well as over the posterior fossa. The occipital lobe was retracted, the transverse sinus ligated, and then the tentorium was split. In 1973, Morrison and King6 added tentorial splitting and sinus ligation to the translabyrin- thine approach in a subtemporal exposure. Hakuba et al, 7 in 1977, modified the Morrison and King approach by preserving the labryrinth, gaining access anterior to the sigmoid sinus, and splitting the tentorium. In 1988, A1-Mefty et als reported 13 petroclival meningiomas operated on using a single temporal and suboccipital bone flap, with drilling of the temporal bone to gain access to the tumor via a presigmoid transtentorial approach. This article details this latter approach. Operative Technique Patient Position The patient is placed in the supine position on the operating table. The table is flexed approximately 30 ~ to allow head and trunk elevation. The patient's ipsilateral shoulder is slightly elevated using a shoulder roll. The head is rotated away from the side of the tumor (approximately 50 ~ ) and is flexed slightly toward the floor. The head is fixed in a three-point headrest. Electrophysiological monitoring is obtained by recording brain-stern auditory evoked potentials and median nerve somatosensory evoked potentials (SSEPs) bilaterally. Facial nerve function, as well as the function of multiple other cranial nerves, can be monitored depending on the size of the lesion and the expected extent of dissection. The Craniotomy Flap A reverse question-mark-shaped incision is made starting at the zygoma anterior to the tragus and is carried approximately From the Department of Neurosurgery, University of Arkansas School of Medicine, Little Rock, AR. Address reprint requests to Ossama AI-Mefty, M.D., Professor and Chairman, Department of Neurosurgery, University of Arkansas School of Medicine, 4301 W. Markham, Slot 507, Little Rock, AR 72205-7199. Copyright 9 1999 by W.B. Saunders Company 1092-440X/99/0202-0003510.00/0 Fig 1, The position of the patient and the skin incision for a right-sided petrosal approach, 58 Operative Techniques in Neurosurge~ Vol 2, No 2 (June), 1999: pp 58-61