Case description: A 10-year-old 7-kg (15.4-lb) neutered male Shih Tzu was referred for evaluation because of a sudden onset of dullness and intermittent vomiting of 1 to 2 weeks' duration. Two days prior to evaluation, clinical signs had worsened and 1 seizure was reported.
Clinical findings: A 3.5 × 2.5-cm soft, dome-shaped mass of the right occipital region of the head was noted on physical examination. Radiography and CT confirmed the presence of the mass and indicated its intra- and extracranial expansion. The MRI images showed compression of the cerebellum by the mass, with distinct margins of hypointensity on both T1- and T2-weighted images.
Treatment and outcome: Surgery was performed, and the mass was completely excised. The dog had mild ataxia, hypermetria, and head tremors after surgery. Histologic examination of the mass yielded a diagnosis of intradiploic epidermoid cyst. On examination 3 weeks after surgery, the previous neurologic signs had resolved. On examination 25 months after surgery, the dog remained free of clinical signs.
Clinical relevance: The present report described the clinical signs, diagnostic imaging results, and successful surgical removal of an intradiploic epidermoid cyst in a dog. Long-term prognosis may be good with complete removal of intradiploic epidermoid cysts in dogs.