A man in his 60s presented with a 6-month history of progressive gait instability, changes in speech, and dysequilibrium. Neurologic examination revealed an ataxic dysarthria, reduced palate elevation on the right, and marked truncal ataxia with postural instability. Magnetic resonance imaging of the brain revealed a dolichoectatic right-dominant vertebrobasilar system with mass effect resulting in flattening of the ventral medulla and displacement of the cervicomedullary junction (Figure). Extensive evaluation to explore genetic, infectious, inflammatory, metabolic, and neurodegenerative causes of progressive ataxia was unrevealing.
