RESUMEN
We encountered a case of spontaneous thymic carcinosarcoma in a young Crl:CD (Sprague Dawley) rat. Grossly, a white multinodular mass replaced the thymus in the thoracic cavity. Histologically, multiple nodules were separated by fibrous stroma, and each nodule included isolated regions that were composed of epithelial or non-epithelial tumor cells. The epithelial tumor cells were relatively large and round to polygonal cells with large nuclei and weakly eosinophilic cytoplasm. These cells were cytokeratin-positive and vimentin-negative. These cells infiltrated the lungs. The non-epithelial tumor cells were poorly differentiated, small, round to spindle-shaped cells with small nuclei and basophilic cytoplasm. These cells were vimentin-positive and mostly cytokeratin-negative. Many islands of cartilage were observed near non-epithelial cells. Based on these findings, the tumor was diagnosed as a primary thymic carcinosarcoma consisting of a malignant thymoma composed of epithelial tumor cells and a mesenchymal chondrosarcoma composed of non-epithelial tumor cells.
RESUMEN
We investigated the influence of repeated intravenous administration of dextrans (DEXs) to rats. Seven-week-old Sprague Dawley rats (6 males/group) were given intravenously 10% saline solutions of dextrans (DEXs), 40 kDa or 200-300 kDa, at a dose level of 5 mL/kg/day for 28 days and they were examined histopathologically. Another group (3 males/group) was administered saline in a similar manner and served as the control. Histopathological changes indicating accumulation of DEXs in the mononuclear phagocyte system (MPS) and the liver were noted in the treated groups. The incidence and severity of the findings were molecular weight-dependent, except for the lungs. These results are considered useful in interpreting data from preclinical studies, in which DEXs or their derivatives are administered as test or control substances.