Abstract
A female, 8-year-old Labrador Retriever with elevation of the right rear limb was referred to our hospital. We found the mass behind the right knee. Although it was diagnosed as osteosarcoma by Tru-cut core biopsy, morphological abnormality of bone and periosteum commonly seen in the case of skeletal osteosarcoma was not evidenced by X-ray and CT examinations. The amputation of the right pelvic limb by disarticulation of the hip was performed. However, on 147 days after surgery the canine patient died from metastases in lung, abdominal cavity and abdominal wall. The case was definitely diagnosed as extraskeletal osteosarcoma behind right knee originating from soft tissue by X-ray and CT images, postoperative course, biological behavior, macroscopic finding and histopathological examination of the tumor.
