Distal Anterior Inferior Cerebellar Artery Syndrome After Acoustic Neuroma Surgery

Objective To define a clinicopathologic syndrome associated with persistent cerebellar dysfunction after acoustic neuroma (AN) excision. Study Design Case series derived from radiographic and clinical chart review. Setting Tertiary referral center. Patients In 12 patients with AN, persistent cerebellar dysfunction developed after AN removal. Each case demonstrated abnormality in the ipsilateral cerebellar peduncle on postoperative magnetic resonance imaging. Main Outcome Measures Cerebellar function and ambulatory status over the first postoperative year. Results On magnetic resonance imaging scans, the extent of cerebellar peduncle infarcts was variable. It ranged from focal brain injury (<1 cm) involving only one third of the peduncle to diffuse defects (>2 cm) spanning the full thickness of the peduncle. Peduncular infarcts were associated with large tumor size (average 3.8 cm, range 2.0–5.5 cm diameter). The long-term functional outcomes (>1 yr) varied. Dysmetria was unchanged or improved in over half of the patients (6 of 11 patients). Gait recovered to normal or to preoperative levels in 5 patients. In the 6 patients with persistent impaired mobility, 2 had mild gait disturbance, 3 required regular use of a cane, and 1 has been dependent on a walker. One patient had sustained mild motor weakness. Three of 11 patients remained dependent on others for activities of daily living. Conclusions Peduncle injury most likely stems from interruption of distal branches of the anterior inferior cerebellar artery (AICA). These small vessels are intimately related to the capsule of the tumor and may supply both the neoplasm and the brain parenchyma. It has long been recognized that interruption of the proximal segment of the AICA results in severe injury to the pons, with devastating neurologic sequelae. A limited AICA syndrome caused by loss of its distal ramifications seems a more plausible explanation for peduncular infarction than either venous insufficiency or direct surgical trauma.