Neoplastic transformation of arteriopathy-derived bone infarct into nascent osteosarcoma in the proximal tibia of a miniature schnauzer

A 9-year-old, entire, male miniature schnauzer with a history of chronic right hindlimb lameness was presented to a referral orthopaedic surgery practice for acute non-weight bearing and suspected cranial cruciate ligament rupture. Radiographs revealed polyostotic bone infarcts, characterised by stippled medullary densities, and an aggressive osteolytic infarct in the right proximal tibia. Histopathology of the amputated limb revealed an arteriopathy of the nutrient artery and a zonal histologic pattern of neoplastic transformation: at the infarct apex, mesenchymal stromal cells were engaged in repair. As the cells proliferated towards the centre of the infarct within an environment of chronic ischaemia, cell features became consistent with low-grade sarcoma, then nascent (early) osteosarcoma. This zonal progression has been described in humans, but not in dogs. It is unknown whether nascent osteosarcoma has the same biologic activity as long-standing osteosarcoma. Veterinarians should be aware of canine bone infarcts and their potential sequelae.