Suprameatal Extension of the Retrosigmoid Approach: Microsurgical Anatomy

OBJECTIVE: This study was conducted to determine whether removing the bony prominence located above the porus of the internal acoustic meatus, called the suprameatal tubercle, and surrounding bone using the retrosigmoid approach would aid in the exposure of tumors that are located predominantly in the cerebellopontine angle but that also extend into the middle cranial fossa in the region of Meckel's cave and thus avoid the need for a supratentorial craniotomy. METHODS: Thirty cerebellopontine angles from 15 cadaveric heads examined using 3 to 40x magnification provided the material for this study. A retrosigmoid craniotomy was completed and the exposure obtained before and after removing the suprameatal tubercle, and the surrounding bone was examined. In some cases, Meckel's cave and the tentorium lateral to the porus of Meckel's cave was opened to aid in the exposure. RESULTS: Removing the suprameatal tubercle and surrounding bone increased the exposure an average of 10.3 mm (range, 8.0-13.0 mm) forward of the exposure, which could be obtained without suprameatal drilling. The extent of bone removal was limited on the lateral side by the posterior and superior semicircular canals and their common crus. CONCLUSION: The suprameatal extension of the retrosigmoid approach will permit removal of some tumors that are located mainly in the posterior fossa but that extend into the middle fossa in the region of Meckel's cave. The exposure can be increased by opening the superior petrosal sinus as it crosses in the upper margin of the porus of Meckel's cave and by opening the tentorium lateral to Meckel's cave.