Extraskeletal Osteosarcoma Induced by a Foreign Body Granuloma.

An 8 yr old spayed female Italian greyhound was presented with a mass in the cranial abdomen. Preliminary evaluation of the dog revealed a large, cavitary, irregularly shaped mass with no definitive association with any abdominal organs. During an exploratory celiotomy, a 16 cm × 12 cm × 6 cm mass was removed. On subsequent histopathology, extraskeletal osteosarcoma induced by a foreign body granuloma was diagnosed. The foreign body granuloma, based on histopathological findings, was suspected to be secondary to a retained surgical sponge from her routine ovariohysterectomy performed 7 yr prior to presentation. Animals with granulomas induced by foreign bodies can remain asymptomatic for years; however, those granulomas can progress to extraskeletal osteosarcomas, which carry a poor prognosis.