ABSTRACT
Arteriovenous malformations (AVMs) of the posterior fossa have been classically divided into cerebellar and brainstem lesions. Intrinsic to this simple classification was the operability of such malformations; cerebellar AVMs were considered in most cases amenable to surgical excision, whereas brainstem AVMs were deemed inoperable. As more experience was gained from direct exploration of these lesions and with the advent of microsurgical techniques, it became apparent that a separate category was necessary for those AVMs located in the cerebellopontine angle (CPA) (1). CPA AVMs may extend along the ventrolateral surface of the brainstem but usually are relatively easy to dissect, inasmuch as a pial-epipial plane of cleavage separates the malformation from the surrounding parenchyma (1). These characteristics allow safe and radical excision from adjacent structures (brainstem, cerebellum) with low rates of mortality but some morbidity related to dysfunction of cranial nerves (CNs) V to XII (1). Other characteristics that differentiate CPA AVMs from other posterior fossa AVMs include the following: unilateral feeders, with the anterior inferior cerebellar artery (AICA) almost invariably involved; superficial venous drainage, usually to the superior petrosal sinus through the petrosal vein; and a close relationship to the nerves in the angle, which makes ipsilateral CN dysfunction (mostly transient) a frequent, sometimes unavoidable consequence of surgical excision (1).
