Aneurysmal bone cyst in a rib of a cat.

An aneurysmal bone cyst was identified in the rib of a 3 1/2-year-old domestic shorthair cat. Surgical excision of the cyst, with reconstruction of the thoracic wall, was performed. Though aneurysmal bone cyst is a benign neoplastic condition that may be associated with locally aggressive growth, it does not metastasize. The condition is rare in any species other than human beings, but has been reported in cats, dogs, and horses.