Oral Myxoma in a Steer
Background: Myxoma is a benign neoplasm of mesenchymal cells producing a myxomatous matrix rich in mucopolysaccharides. This tumor occasionally has been described in older dogs and cats, and rarely occurs in other species. In ruminants myxomas can be found in the rumen and omasum, but there are no reports of these neoplasms involving the oral cavity of cattle. Only one case of myxoma was diagnosed in a 40-year study of 606 neoplasms in cattle in South Africa. Similar retrospective studies done in cattle from southern and northeastern Brazil also detected a single case of cutaneous myxoma. The current study reports the clinical and pathological findings of a rare occurrence of bovine oral myxoma.
Case: A 22-month-old male crossbreed steer (Bosindicus) from the municipality of Rio Verde, GO (17°44′42″S 50°55′00″W), Brazil, presented a history of sialorrhea. There is no another affected animal in the herd. Clinical evaluation revealed mild swelling in the lower incisive gum. Treatment with flumetasone IM for three consecutive days was performed. Two months after this procedure, there was a considerable increase in the size to a flat, firm mass of 16x13x9 cm. Other clinical signs included emaciation and severe difficulty in feeding and drinking water. After surgical excision, fragments of the tumor were collected for histopathology. There is no local recurrence within approximately one year of the surgery. Microscopically, the lamina propria was found to be expanded and replaced by a nonencapsulated, moderately cellular, poorly demarcated, neoplastic proliferation. The lesion was composed of numerous loosely arranged bundles of cells in an abundant myxoid matrix. The bulk of the tumor parenchyma was formed by spindle or stellate cells with poorly demarcated borders and scant, eosinophilic cytoplasm. The nuclei were oval and hyperchromatic. Mild anisocytosis and anisokaryosis were present, along with rare mitotic figures. The myxoid matrix presented strong positive labeling to mucin by the Alcian blue staining. Based on the anatomopathological and histochemical findings, a diagnosis of myxoma was established.
Discussion: Neoplasms of connective tissue originate from poorly differentiated fibroblasts and can produce collagenous (fibroma/fibrosarcoma) or mucinous (myxoma/myxosarcoma) stroma. In some cases, it is difficult to establish a histopathological classification and to distinguish between benign and malignant neoplasms, for which assessment of cell morphology, mitotic index, and biologic behavior are required. Very few cases of myxoma have been previously reported in cattle, this neoplasm and it was never diagnosed in the oral cavity of this species. Thre majority of neoplasms diagnosed in the oral cavity of cattle are squamous cell carcinomas and papillomas, although sporadic cases of lingual fibroma, lingual mastocytoma, odontoma and ameloblastic fibroma have been described. In the current case, the steer presented weight loss and difficulty in feeding and drinking water, probably due to the large volume of the neoplasm. Similar clinical signs can occur in cattle affected by other types of large neoplasms in the oral cavity. After surgical excision, the animal of the current report presented general improvement and considerable weight gain. The myxoma-related pathologic findings observed in the present case are similar to those described in other studies. Because myxoma is considered an infiltrative neoplasm, postoperative recurrence can occur; however, this was not noted in the current case and reports of myxoma in other species. The main differential diagnosis for myxoma is fibroma; the presence of mucin (Alcian blue positive) in the intercellular matrix as seen in the current case confirms the diagnosis of myxoma.
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