Radiographic, Citomorphological, and Histochemical Characterization of the Skin Mixosarcoma in a Bitch

Background: Myxosarcoma is a malignant mesenchymal tumor that arises from fibroblasts and is characterized by a low frequency of metastases, which in turn are highly invasive locally. Even though this type of tumor is relatively well documented, its radiographic and cytomorphological aspects are rarely described. The present report describes a case of cutaneous myxosarcoma in a female dog, and highlights radiographic, cytological, and histopathological findings. Case: An 11-year-old female mongrel dog was examined at the Veterinary Hospital of Federal University of Paraiba. The patient exhibited a firm 20 cm-wide mass covered by skin in the left abdominal wall, a lesion that had been developing for approximately five months. During the clinical examination, the patient demonstrated apathy and difficulty to stand. Initially, exams requested included radiography, ultrasonography, and cytological analysis of biopsy material obtained by fine needle aspiration (FNA). Radiography and ultrasonography were used to investigate the extent of the tumor, as well as invasion of other organs. Radiography revealed that the tumor was radiopaque, homogeneous, and restricted to the skin and subcutaneous tissue; no metastases were observed. Cytological examination allowed observation of a hypocellular sample predominantly composed of isolated pleomorphic fusiform cells embedded in a discrete homogeneous eosinophilic material. These cells exhibited a moderate, well delimited cytoplasm with multiple vacuoles; the end opposed to the nucleus was slender. Their nuclei were eccentric, with punctate chromatin and inconspicuous nucleoli. The patient was subjected to complete surgical excision of the tumor, and the surgical piece was submitted to histopathological examination. The mass was described as single and firm; its dimensions were 20 cm x 16 cm x 15 cm, and its weight was 2.5 kg. Fragments were processed and stained with hematoxylin and eosin (HE) or alcian blue (AB) for evaluation by optical microscopy. Histopathology revealed an infiltrative, expansive, non-encapsulated mass characterized by mesenchymal cells ranging from elongated to stellate. These cells were well individualized, had a scant to moderate cytoplasm, indistinct and slightly eosinophilic borders, and a nucleus that varied from oval to stellate in shape, with highly condensed chromatin and inconspicuous nucleoli. AB-stained specimens exhibited an extensive myxomatous matrix stained in blue, which was intertwined with neoplastic cells. Therefore, the diagnosis of cutaneous myxosarcoma was confirmed. Discussion: The diagnosis of myxosarcoma was established on the basis of radiographic and cytological findings, and it was confirmed by histopathological examination, which sped up decision-making and completion of the case. Tumors of this group are not accompanied by paraneoplastic syndromes; however, given the size and weight of the mass under study, pain may have been the triggering factor of the apathy and difficulty to stand observed here. The age of the patient and the occurrence of the tumor in the skin are in agreement with the literature; however, presence of the tumor in the abdominal skin is uncommon, and this fact prevented definition of a clinical suspicion prior to cytopathological examination. Radiographic examination confirmed the dimensions and extent of the mass; additionally, it allowed exclusion of occurrence of metastatic foci. Cytologically, the material analyzed was consistent with literature findings for canine myxosarcoma samples, so that cytopathological examination already suggested occurrence of such condition in this case. Histopathological evaluation was indispensable for establishment of the diagnosis as well as AB staining, which highlighted high amounts of glycosaminoglycans among the neoplastic cells, which led to confirmation of the diagnosis.