Vaginal leiomyosarcoma in a degu (Octodon degus): a case report

A 6-year-old pet female degu (Octodon degus), in good body condition, was referred to a clinic with the presence of a large tumour in the anogenital area. The mass was bluntly dissected from the surrounding skin and muscles. The medial part of the tumour was associated with the vaginal wall which was also excised with 2 mm margins. No visible changes on the inner vaginal surface were seen. On gross examination the surface of the mass was glossy and pink-coloured; the cut surface was grey to red with greyish-white foci in a part of the mass. Histopathological examination showed a tumour composed of pleomorphic spindle to ovoid cells forming interlacing bundles and variably dense fibrous connective tissue separated by streams of neoplastic cells. Several smaller foci of coagulation necrosis were present within the tumour tissue. The neoplastic cells exhibited a high mitotic index, which ranged from six to seven mitoses per 10 high power fields. By immunohistochemical examination the positivity of neoplastic cells was demonstrated with smooth muscle actin (SMA) and vimentin, while no immunoreactivity was acquired for cytokeratins. Based on morphological features of the tumour and immunohistochemical examination a diagnosis of vaginal leiomyosarcoma was made. To our knowledge, this is the first report of a vaginal leiomyosarcoma in a degu.