Phenotypic variation of thymic epithelial cells and partial spontaneous regression in thymoma of a cow

AbstractThymoma was recognized in a 12-year-old Holstein dairy cow presenting with no significant clinical signs. The animal was conventionally slaughtered at an abattoir and, on postmortem examination, a spherical tumor mass was found in the anterior region of the mediastinum. Histologically, the tumor was fibrously encapsulated and exhibiting varying-sized cystoid cavities containing serous fluid and necrotic and hemorrhagic foci. No architectural features showing distinct characteristics to a sufficient degree to allow identification of the thymus or other organs could be seen. The tumor showed diffuse solid sheet-like or nodular patterns of proliferation and consisted of a dual cell population: one was neoplastic epithelial cells that were immunohistochemically positive for cytokeratin, and the other was T lymphocytes that exhibited positive immunohistochemical staining with CD3. This finding enabled a diagnosis of mixed thymoma to be made. Neoplastic epithelial cells represented a wide spectrum of phenotypic expression, including (1) spindle shaped cells with a chiasmus-like, interlacing fascicular, or storiform growth pattern; (2) small, round to oval cells with scant cytoplasm showing indistinct boundary of cells; (3) large cells arranged in a solid sheet-like pattern; (4) vacuolated cells similar to signet ring cells; (5) clear cells that had defined cell membranes; and (6) occasional formation of micronodules composed of neoplastic epithelial cells. In addition, some...

Source: Comparative Clinical Pathology - September 14, 2017 Category: Pathology Source Type: research