Case 170317-1

Eleven-year-old, castrated, male Shetland sheepdog

During a prophylactic dental procedure at the referring veterinarian, a soft tissue mass was observed on the ventral aspect of the tongue, halfway between the base and midline. The mass was removed and it was diagnosed by histopathology as a moderately differentiated, incompletely excised liposarcoma (low-grade liposarcoma).

Approximately one month later a nodule was identified on the tongue in the region of the previous excision. The nodule was removed was diagnosed by histopathology as a completely excised xanthoma.

The original biopsy was evaluated for a second opinion, because of the apparently contradictory diagnoses.

No gross description was provided.

Two sections of tongue are examined, in which a poorly demarcated, infiltrative, unencapsulated mass of large vacuolated cells is embedded in the superficial submucosa. The mass extends to the section margins. The neoplastic cells are arranged in sheets that contain strands of pre-existing collagen and blood vessels. The cells are polyhedral, with distinct cell borders and moderate to large numbers of unstained, sharply demarcated vacuoles. The neoplastic cells have round to ovoid nuclei with hyperchromatic, often peripheralized chromatin. A single nucleolus is visible in some cells. Anisocytosis and anisokaryosis are moderate and no mitotic figures are seen. Numerous macrophages are scattered among the neoplastic cells. A few multi-nucleated cells are present and a small number of lymphocytes and plasma cells occasionally surround vessels, which are lined with plump (reactive) endothelium.

Immunohistochemistry was performed for CD204. Large numbers of macrophages that are scattered throughout the neoplastic population have strong cytoplasmic and membranous reactivity. Many neoplastic cells are limned by intensely stained, thin extensions of macrophage between and around them. However, the neoplastic cells, themselves, have no immunoreactivity for CD204.

Tongue: Liposarcoma

The sections from the subsequent re-excision of the mass were originally diagnosed at the VMTH as xanthoma. However, in this re-evaluation of the original mass, it was decided that the diagnosis of liposarcoma was apparently correct. The neoplastic cells in the original sample, evaluated here, have greater cellular atypia and anisokaryosis than the sample from the second biopsy. In addition, many large macrophages infiltrate the mass, and these macrophages partially obscured the neoplastic cells in the second sample. Immunohistochemistry helped to better contrast the inflammatory cells from the neoplastic population.

Multiple conference participants were skeptical of the diagnosis of liposarcoma. The possibility of a granular cell tumor was suggested, although these neoplastic cells lack the prominent granules, which are a feature of neoplastic granular cells. An Oil Red O stain was also suggested, however no unprocessed tissue is available. A periodic acid-Schiff stain (PAS) might also be helpful, because the cytoplasm of a granular-cell tumor would likely be PAS-positive. A PAS-positive reaction of the cytoplasm could also help rule out lipid in the vacuoles of the neoplastic cells. Both liposarcomas and granular-cell tumors are sporadically reported in the tongue of the dog.