Quantitative comparison of Kawase's approach versus the retrosigmoid approach: implications for tumors involving both middle and posterior fossae.

OBJECTIVE: Few quantitative data are available to describe Kawase's exposure of the posterior fossa. We used a cadaveric model to compare Kawase's and the retrosigmoid approach to the petroclival region. METHODS: Eighteen cadaveric specimens were dissected and analyzed (6 retrosigmoid, 6 Kawase's, and 6 retrosigmoid intradural suprameatal approaches). Clival and brainstem working areas and surgical freedom were measured. RESULTS: The retrosigmoid approach provided a significantly larger clival and brainstem working area than Kawase's approach. Surgical freedom at the trigeminal root entry zone, origin of the anterior inferior cerebellar artery, and Dorello's canal was equivalent across approaches. Kawase's approach provided the most surgical freedom at the trigeminal porus. However, the addition of a suprameatal extension significantly improved the surgical freedom provided by the retrosigmoid approach. CONCLUSION: The retrosigmoid approach is a powerful approach to lesions of the cerebellopontine angle and ventral brainstem. Lesions involving the trigeminal porus and Meckel's cave can be approached through Kawase's approach or a suprameatal extension of the retrosigmoid approach. Kawase's approach is best suited for accessing middle fossa lesions with smaller petroclival components located above the internal auditory canal.