Approaches to the Cerebellopontine Angle
The cerebellopontine angle (CPA) is formed by the petrosal cerebellar surface, middle cerebellar peduncle, lateral pons, petrosal surface of the petrous bone, and clival portion of the occipital bone. While only accounting for 10–15% of intracranial tumors, CPA tumors are the most common tumors of the posterior fossa. Vestibular schwannomas (VS) account for 85% of masses in this region, while meningiomas, epidermoids (primary cholesteatomas), and trigeminal, facial, and lower cranial nerve schwannomas constitute the majority of non-VS CPA tumors . The three primary approaches to the CPA are the retrosigmoid, translabyrinthine, and middle fossa approaches. The optimal approach for a given patient depends on the tumor’s growth pattern (e.g., the middle fossa approach is suboptimal for tumors with extensive growth in the CPA), the patient’s hearing status, the surgeon’s expertise in a given approach, and the goals of the operation. Furthermore, the density of crucial structures in this region makes careful preoperative assessment and planning essential in complication avoidance . The retrosigmoid approach allows for hearing preservation and resection of lesions with significant extension into the CPA, though it requires cerebellar retraction and offers limited access to the fundus of the internal auditory canal (IAC). In contrast, the translabyrinthine approach requires very little brain retraction and has no limitation on tumor size or IAC exposure but does require sacrificing hearing. The middle fossa approach, while maintaining hearing preservation, is limited by the extension of the mass lesion into the CPA (~10 mm). In this chapter, we elaborate on these approaches and their variations. We emphasize that these approaches are a continuum of trajectories progressing from an exposure of the face of the petrous bone (retrosigmoid approach) to an anterior view of the brainstem (middle fossa approach; Fig. 5.1). Exposure and comparison of the three main approaches in the context of a VS are summarized in Tables 5.1 and 5.2.