Mandibular Osteoma in a Haflinger Mare: Clinical and Pathological Features.

An 11-year-old Haflinger mare developed a slowly growing mass on her mandible, diagnosed as mandibular osteoma, a type of non-cancerous bone growth. The osteoma was successfully removed and the mare had a good prognosis.

Clinical Presentation and Diagnosis

• The Haflinger mare presented with a mass on the ventral aspect of the mandible, which is the underside or the lower jaw. The mass was growing slowly and was very firm, cold, and not causing the horse any pain.
• The mass was unique in its pedunculated shape – meaning it was attached to the mandibular cortex, or outer layer of the mandible, by a stem or stalk.
• Radiographic examinations showed a radiopaque, multi-lobular, “mushroom-like” lesion arising from the mandibular cortex but not involving the bone marrow cavity.
• Based on the mare’s history, clinical findings, diagnostic imaging, and pathological features, the diagnosis of mandibular osteoma was supported.

Pathological Features

• The mass was excised and microscopic examinations revealed it mainly consisted of bone trabeculae – the structural unit of the spongy bone tissue, which was covered by a thick layer of connective tissue resembling the periosteum, a very dense, fibrous membrane covering the surface of bones.
• The presence of a mass or lesion with a stalk arising from the bone surface was identified as a key feature suggesting osteoma.

Comparative Analysis and Prognosis

• Equine osteomas usually occur in paranasal sinuses and the rostral mandible (towards the nose), and often resemble other neoplastic and neoplastic-like conditions, such as ossifying fibroma and fibrous dysplasia.
• In this case, the osteoma prognosis was good. The key to successful treatment of these types of growths is complete removal, which can be influenced by the location and size of the mass.