Aneurysmal bone cyst in a dog.

A one-year-old male mongrel dog was referred to the Veterinary Clinic with a several-week history of lameness and pain of the right front leg. Radiological examination of the right humerus revealed a cystic lesion at the distal end of the bone; the lesion was nodular in a gross appearance. Histologically, the nodular lesion consisted of large areas of haemorrhage and thick fibrous trabeculae mixed with a variably dilated cavernous structure of blood vessels attributed to haemangiosarcoma. Based on these findings, aneurysmal bone cyst secondary to the tumour was diagnosed.