Spleen - Hyperplasia, Lymphocyte

Lymphocyte hyperplasia of the spleen is an increase in the number of lymphocytes outside the range of normal compared with concurrent controls. The result can be variable increases in the area and number of white pulp elements (periarteriolar lymphoid sheaths [PALS], follicles, and/or marginal zones) (Figure 1 and Figure 2, arrows). This lesion can be focal or generalized. Lymphocyte hyperplasia in the spleen occurs more frequently in mice than in rats, and female mice are more commonly affected than male mice. Marked lymphocyte hyperplasia can be difficult to distinguish from early lymphoma of the spleen; however, the splenic architecture (white pulp and red pulp compartments) should be maintained with lymphocyte hyperplasia (Figure 1 and Figure 2), whereas loss of the splenic architecture would be expected with lymphoma. With generalized lymphocyte hyperplasia, there can be confluency of the PALS regions (Figure 1), so cellular morphology should be evaluated to differentiate from lymphoma. Lymphoma consists of monomorphic (or pleomorphic) neoplastic lymphocytes with increased cellular atypia, whereas lymphocyte hyperplasia consists of increased numbers of normal, mature lymphocytes.