Intracranial dermoid cyst in a dog.

A 7-year-old spayed bitch had a 3-year history of episodes of hind-limb weakness and ataxia. Neurologic abnormalities consisted of deficits in postural reactions, spinal reflexes, and conscious proprioception. A right-sided head tilt also was observed. Immediately after cervical radiography, CSF tap, and electroencephalography, the dog was alert, but it was found comatose the next morning and died within an hour. At necropsy, a 1.6- x 0.8- x 1.5-cm, thinly encapsulated mass was found on the left cerebellar peduncle. It had caused dorsal displacement of the left portion of the cerebellum and ventral compression of the fourth ventricle. Histologically, the mass was determined to be a dermoid cyst.