Petroclival meningiomas: Predictive parameters for transpetrosal approaches

OBJECTIVE: To determine parameters that influence the selection of the prop er petrosal approach or combined approaches for the excision of petroclival meningiomas. METHODS: We dissected 15 cadaver heads, inspected the petroclival region in 50 dry human skulls, and performed a retrospective analysis of the cases o f 35 patients with petroclival meningiomas who underwent surgery via transp etrosal approaches. RESULTS: The petroclival region was divided into three "zones" based on the extent of surgical exposure achieved via the petrosal approaches with micr oscopic dissection of 15 preserved and silicone-injected cadaveric heads an d with the measurements of 50 dry skulls. Zone I, defined as the area from the dorsum sellae to the internal auditory canal, is accessible via the ant erior petrosal approach. Zone II, defined as the area from the internal aud itory canal to the upper border of the jugular tubercle, is easily accessib le in its lateral portion via the posterior petrosal approach. The medial p ortion of Zone II, the "central clival depression," is accessible only with cochlear resection and posterior facial nerve transposition. Zone III, def ined as the area from the upper border of the jugular tubercle to the lower edge of the foramen magnum, is accessible via a suboccipital/transcondylar approach. The retrospective analysis of the cases of 35 patients who under went transpetrosal resection of petroclival meningiomas between 1991 and 19 98 was used to determine the predictive value of these anatomic parameters. The degree of tumor resection was analyzed with a novel grading scale comb ining the percentage of resection and the percentage of brainstem reexpansi on. Total excision was achieved in 37% of the patients and complete brainst em reexpansion was achieved in an additional 40%. Residual tumor was concen trated in the central clival depression in Zone II, as predicted by anatomi c parameters, and around infiltrated neurovascular structures. New cranial nerve deficit occurred in 31% of the patients in the early postoperative pe riod and improved to 17% at 6 months. Major morbidity occurred in 9% of the patients, and mortality was 0%. Early Karnofsky scores were reduced in 37% of the patients, but 6-month Karnofsky scores were equal to preoperative b aseline scores or improved in 91%. CONCLUSION: Anatomic parameters can predict the resectability of petrocliva l meningiomas. Judicious application of cytoreductive surgery in selected p atients maintains an acceptable morbidity and achieves adequate brainstem r eexpansion.