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Case report: Multilobular Osteochondrosarcoma in a Boxer

A six year old female, neutered Boxer presented with a non-painful, rapidly growing, fixed, firm, subcuticular mass on the head. Clinical examination was otherwise unremarkable. Wedge biopsies indicated a diagnosis of multilobular bone tumour. CT scans (figs.1+2) revealed the mass to have arisen from the interparietal bone, extending peripherally to invade the overlying masticatory muscles. There was disruption to the trabecular pattern within the underlying bone. There was also evidence of tumour seeding along biopsy tracts to the skin. Staging the tumour revealed no gross evidence of pulmonary or hepatic metastasis.

CT scan of osteochondrosarcomaThe mass was removed, along with grossly normal margins of 2 to 3cm. This necessitated removal of a section of the skull. The dura mater was left intact and the defect covered by rotation flaps of temporalis muscle and fascia. The skin deficit was closed by local undermining. Passive drains were left in place for several days, and the wound healed uneventfully. Histology revealed a definitive diagnosis of multilobular osteochondrosarcoma.

CT scan of osteochondrosarcoma 2These tumours (also called osteomas/ chondromas/ chondroma rodens) usually arise from the membranous bones of the skull, but occasionally involve the vertebrae. Affected animals have historically been given a guarded prognosis, on the basis of local aggressive tumour growth with a mass effect on adjacent vital structures. More recent, radical surgical management of such cases has increased the likelihood of achieving local cure. This has allowed long-term evaluation of the condition. It has subsequently become apparent that approximately half of these cases will go on to develop distant metastases in the future. The prognosis for this condition must therefore remain guarded, even with cases amenable to resection with clear margins. Due to the rarity of the condition, adjunctive chemotherapy has not been evaluated for its impact on mean survival times.