Chapter 64: Nonacoustic Lesions of the Cerebellopontine Angle

INTRODUCTION

Vestibular schwannomas (VSs), previously known as acoustic neuromas, account for 80% of all lesions of the cerebellopontine angle (CPA). This chapter will focus on the other 20%—a group whose diverse pathologies share a common clinical presentation of injury to the cochlea-vestibular system. The most common of these are meningiomas, followed by epidermoids and lipomas. Because their symptomatology is often similar, differentiation between various pathologies of the CPA relies heavily on their imaging characteristics.

The CPA is a potential space filled with cerebrospinal fluid (CSF) in the posterior cranial fossa bounded by the temporal bone, the cerebellum, and the brainstem. The CPA is traversed by cranial nerves V to XI and most prominently the facial (CN VII) and vestibulocochlear (CN VIII) nerves. CPA tumors account for 10% of all intracranial tumors (Table 64–1). VSs, meningiomas, epidermoids, and lipomas account for 95% of CPA lesions. The remaining 5% is composed of a diverse group of pathologies including arachnoid cysts, lower CN schwannomas, intra-axial tumors, metastases, vascular lesions (eg, paragangliomas and hemangiomas), and lesions extending from the skull base (cholesterol granulomas and chordomas). CPA lesions become clinically symptomatic by causing compression of the neurovascular structures in and around the CPA. The classic description of these symptoms initially includes asymmetric sensorineural hearing loss, tinnitus, and/or vertigo, and may progress to altered facial sensation, facial pain, facial palsy, nystagmus, vocal cord palsy, dysphagia, diplopia, respiratory compromise, and, in rare cases, death (Table 64–2).

MENINGIOMAS