34th Annual Scientific Meeting proceedings

Objectives:

Osteosarcoma is a rare type of malignant mesenchymal tumour of bone in horses. In most cases they occur in the mandible of young horses. Most osteosarcomas described in the literature are osteoblastic or fibroblastic osteosarcomas. There is only 1 case described of a horse with a chondroblastic osteosarcoma occurring in the humerus. This case report describes the histopathologic findings, surgical treatment and short-term follow-up of a mesenchymal neoplasm suggestive of chondroblastic osteosarcoma in the right maxillary and frontal sinuses.

Methods:

A 21-year-old Dutch Warmblood was admitted to the clinic with stridor, right sided exophthalmos and facial deformity. Endoscopic examination did not reveal the cause of the clinical signs. On radiographic examination, there was a homogenous opacity in the right rostral and caudal maxillary sinuses and right frontal sinus.

Outcome:

Complete removal of the mass was performed in the standing horse. A right maxillary and frontal bone flap were created. Elevation of the bone flaps exposed an expansive and invasive beige-brown coloured and partially mineralized soft mass. The mass was removed by blunt dissection. Histopathology results were suggestive of a chondroblastic osteosarcoma. Follow-up 3 months post-operatively revealed no radiographic signs of opacity in the sinuses, almost complete resolution of the stridor and improvement in the exophthalmos and facial deformity.

Conclusions:

This case report describes the diagnosis and successful treatment of a putative chondroblastic osteosarcoma present in the right maxillary and frontal sinus of a horse.