Localized lymphoid hyperplasia of the rectum representing progressive transformation of the germinal center. A report of two cases.

Histologically, benign lymphoid hyperplasia (BLH) of the rectum is usually characterized by large lymphoid follicles with active germinal centers, and a narrow surrounding mantle zone and marginal zone. We present two cases of BLH of the rectum demonstrating progressive transformation of the germinal center (PTGC). The patients were 50- and 71-year-old Japanese women. Colonoscopy demonstrated small sessile polyps in both cases. The resected specimen contained numerous lymphoid follicles with active germinal centers and a portion of the lymphoid follicles exhibited PTGC. The area showing PTGC contained a few large lymphoid cells resembling lymphocytic and histiocytic Reed-Sternberg cells of nodular lymphocyte-predominant Hodgkin lymphoma. These PTGC contained small- to-medium clusters of epithelioid cells in both cases. In situ hybridization studies demonstrated scattered Epstein-Barr virus (EBV)-encoded small RNA-positive medium and large lymphoid cells and crypt epithelium in both lesions. EBV may be involved in the etiology of a subset of BLH of the rectum. However, reactivity of lymphoid cells for EBV has been reported in lymphoid tissues in a high percentage of "normal" individuals. The etiology of BLH of the rectum remains unclear.