A 1 year old labrador retriever had a small palpable mass on the medial side of the antebrachium proximal to the radiocarpal joint. The lesion was not painful on palpation and the dog was not lame. The owner thought the lesion had been present all of the dog’s life but thought it may have become larger.Decide the clinical importance of the lesion and a name for the lesion. Radiographic diagnosis The lesion is called an osteochondroma and is included in discussions of both developmental bone lesions as well as benign bone tumors. Osteochondromas are solitary or multiple and are hereditary in dogs, horse, and man. Their radiographic appearance is a smooth margined protuberance of bone usually perpendicular from the cortical surface. The lesions have both pedunculated as well as sessile attachments. They usually have a dense cortical border and a center of cancellous bone that is continuous with the underlying medullary cavity of the parent bone.The tip of the exostosis is covered by a hyaline cartilage cap that acts as a growth plate and disappears at the time of skeletal maturation. The lesions are often located in the metaphyseal region of long bones and are often found on the distal radius and ulna. Other bones including those in the spine can be affected.The lesion in this dog has not interfered with skeletal growth and is a “leave alone” lesion meaning that it has radiographic characteristics that are benign in nature and it does not cause clinical signs. Therefore, it does not require surgical removal either for diagnosis or for clinical reasons.This is a similar lesion on another dog that presented with the lesion palpable on the distal ulna. The dog had a slightly abnormal gait and minimal external rotation of the foot.This osteochondroma is more pedundulated and has interfered with skeletal growth causing a shortening of the ulna. Note the resulting proximal position of the styloid process of the ulna (arrow) and the resulting curvature of the distal radius. The radiocarpal joint is angled (lines).Compare these findings with the more normal growth in the first patient.The same lesion can be present without secondary effects and be a “leave alone” lesion and be present throughout life or it can interfere with skeletal maturation of a bone and require surgical correction. Joe P. MorganProfessor EmeritusDepartment of Surgical and Radiological SciencesSchool of Veterinary MedicineUniversity of CaliforniaDavis, CA 95616jpmorgan@ucdavis.edu
