Highly aggressive non-metastatic splenic stromal cell tumor in 11-week-old Wistar rat

A rare case of splenic stromal cell tumor was diagnosed in a male Wistar rat during repeated dose oral gavage immunotoxicity study. The rat was eleven-week-old and weighing around 360.23 g. During terminal sacrifice, spleen showed prominent nodules protruding out of the splenic parenchyma. On incision, nodules were white and firm with multiple reddish pinpoint foci. Microscopically, nodules showed partially encapsulated, densely packed, highly pleomorphic anaplastic cells compressing the splenic parenchyma. These cells appeared round to oval to pear shaped with tapering ends. Cellular atypia and few bizarre cells arranged in whirling and storiform patterns. The cells had scant, inconspicuous, baso-eosinophilic cytoplasm with indistinct cytoplasmic borders. The nuclei were vesicular, hyperchromatic with finely granular nuclear chromatin and had one or two prominent nucleoli with mitotic figures. Area of necrosis and haemorrhages were encapsulated by a thick band of proliferating fibrous connective tissue surrounding the concentric layers of fibrin deposition. On the basis of gross and histopathological findings, the present case was diagnosed as splenic stromal cell tumor.