Petroclival meningiomas: predictive parameters for transpetrosal approaches.

OBJECTIVE: To determine parameters that influence the selection of the proper 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 of 35 patients with petroclival meningiomas who underwent surgery via transpetrosal approaches.

RESULTS: The petroclival region was divided into three "zones" based on the extent of surgical exposure achieved via the petrosal approaches with microscopic dissection of 15 preserved and silicone-injected cadaveric heads and 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 anterior petrosal approach. Zone II, defined as the area from the internal auditory canal to the upper border of the jugular tubercle, is easily accessible in its lateral portion via the posterior petrosal approach. The medial portion of Zone II, the "central clival depression," is accessible only with cochlear resection and posterior facial nerve transposition. Zone III, defined 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 underwent transpetrosal resection of petroclival meningiomas between 1991 and 1998 was used to determine the predictive value of these anatomic parameters. The degree of tumor resection was analyzed with a novel grading scale combining the percentage of resection and the percentage of brainstem reexpansion. Total excision was achieved in 37% of the patients and complete brainstem reexpansion was achieved in an additional 40%. Residual tumor was concentrated in the central clival depression in Zone II, as predicted by anatomic parameters, and around infiltrated neurovascular structures. New cranial nerve deficit occurred in 31% of the patients in the early postoperative period 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 baseline scores or improved in 91%.

CONCLUSION: Anatomic parameters can predict the resectability of petroclival meningiomas. Judicious application of cytoreductive surgery in selected patients maintains an acceptable morbidity and achieves adequate brainstem reexpansion.