Malignant mesenchymoma associated with an unusual vasoinvasive metastasis in a dog

A case of hepatic leiomyosarcoma with osteosarcomatous differentiation (malignant mesenchymoma) in a dog

A rare spontaneous hepatic leiomyosarcoma with osteosarcomatous differentiation was observed in a female beagle dog and its morphological and immunohistochemical characteristics were examined. Upon necropsy, an endoceliac mass originating from the liver was detected, which was composed of hematoid fluid-filled cysts and white to grayish solid tissue. There were no macroscopic findings in other organ systems. Histopathologically, the hepatic mass consisted of two different mesenchymal components. One form was spindle cells arranged in interlacing fascicles immunohistochemically positive for smooth muscle actin (SMA) and smoothelin, indicating leiomyosarcomatous differentiation. The other form was composed of short spindle cells positive for S-100 and was producing various amounts of eosinophilic osteoid and trabecula-like matrices positive for osteocalcin, indicating osteosarcomatous differentiation. In addition, invasive growth in the hepatic parenchyma and cell atypia were observed. Based on these findings, the mass was diagnosed as hepatic leiomyosarcoma with osteosarcomatous differentiation (malignant mesenchymoma), which might be derived from undifferentiated mesenchymal cells.

Disseminated Liposarcoma in a Dog

A 9-year-old, female Mongrel dog was presented for posterior hindlimb weakness, inability to stand, and pain in the lumbosacral and pelvic regions. Radiography revealed a lytic lesion extending from L5 to L6 to the ilium. At necropsy, an 8 − 2 to 3.2 − 3 cm, irregular, white, firm mass was identified extending from the left dorsolateral aspect of the L6 vertebrae to the sacrum, crossing the sacroiliac joint to the ilium, and reaching the acetabulum without affecting the joint cartilage. Tumor masses were also present bilaterally near the costochondral junction of several ribs. White, soft nodules were present in the heart, pericardium, lungs, spleen, and kidneys as well. Histologically, osteolysis with disruption of the cortical bone and reactive bone with the presence of multinucleated osteoclasts was noted. Neoplastic cells consisted of variable, small basophilic round cells (SBRC) with very scant cytoplasm, larger polygonal cells with abundant eosinophilic cytoplasm, and vacuolated cells resembling adipocytes. Within the marrow cavity, vacuolated cells with necrosis predominated, whereas in periosteal areas, polygonal and vacuolated cells that were mixed with a lower percentage of SBRC were more common. In the lungs and heart, SBRC predominated, and in the spleen, polygonal cells were more numerous. Tumor cells stained positive for vimentin and S-100 and stained negative for CD99, neuron-specific enolase, synaptophysin, chromogranin A, cytokeratins, desmin, myoglobin, and actin. This tumor most likely arose from the marrow cavity of the L6 and later invaded through the vertebral body into adjacent vertebrae and various visceral sites.

Malignant mesenchymoma of the heart base in a dog with infiltration of the pericardium and metastasis to the lung

A 9-year-old male rottweiler was presented with abdominal distension, ascites and respiratory distress and marked bulging in the perineal region. At necropsy examination the animal had profuse ascites and hydropericardium and a multinodular mass in the right auricle of the heart infiltrating the epicardium and pericardium and metastasizing to the caudal lobe of the left lung. Microscopically and immunohistochemically the tumour was composed of neoplastic cells with muscular, cartilaginous and adipose differentiation. A diagnosis of malignant mesenchymoma with leiomyosarcomatous (≈ 50%), rhabdomyosarcomatous (≈ 30%), chondrosarcomatous (25%) and liposarcomatous (5%) components was made. Metastatic malignant mesenchymoma has not been reported previously at this site in the dog.

An intra-abdominal malignant mesenchymoma associated with nonabsorbable sutures in a ferret (Mustela putorius furo)

A 6-year-old ferret (Mustela putorius furo) was presented with abdominal enlargement. Clinical examination revealed an intra-abdominal mass measuring approximately 5 cm in diameter. Abdominal survey radiographs revealed a sharply marginated mass with multifocal radiodense foci, suggestive of pathologic calcification. A complete blood cell count revealed a moderate, normocytic, normochromic, nonregenerative anemia. The mass was surgically removed en bloc, fixed in 10% neutral buffered formalin solution, and routinely processed for histologic and immunohistochemical investigation. The neoplastic tissue consisted of a mixed neoplastic cell population, including osteosarcoma and fibrosarcoma components. Immunohistochemistry revealed that both neoplastic cell populations were positive for vimentin and negative for actin (smooth and striated), desmin, and myoglobin. Nonabsorbable suture material was admixed with the neoplastic tissue in the histologic section. This material was birefringent when viewed microscopically under polarized light.

Intermandibular malignant mesenchymoma in a crossbreed dog

A 12-year-old German shepherd crossbreed dog was presented with a submandibular mass that was initially diagnosed as myxosarcoma on incisional biopsy. Chest radiographs were taken for staging, and magnetic resonance imaging was performed to assess the feasibility of cytoreductive surgery before adjuvant radiotherapy. The dog underwent debulking surgery, and histology permitted reclassification of the tumour as a malignant mesenchymoma (with myxosarcomatous and osteosarcomatous differentiation). The dog was subsequently treated with four fractions of radiotherapy given at seven-day intervals and three doses of carboplatin. The dog remained stable following therapy until its condition acutely deteriorated, and it was euthanased 153 days after surgery. On postmortem examination, there were no signs of local tumour recurrence, but metastases were observed both in the thorax and in the abdomen.