Lymphoma arising in mucosa-associated lymphoid tissue of the duodenal bulb.

We report a case of low-grade B-cell lymphoma of the duodenal bulb arising from mucosa-associated lymphoid tissue. A barium swallow and an endoscopic examination showed multiple elevated, irregularly contoured lesions limited to the duodenal bulb. Endoscopic biopsy specimens were highly suggestive of non-Hodgkin's lymphoma. The resected specimen showed a gyriform mucosal elevation measuring 3 x 2cm in extent, with multiple small polypoid elevations scattered around it. Histologically, the small lymphocytes constituting the tumor infiltrated the duodenal mucosa and submucosa. The neoplastic centrocyte-like cells tended to grow around reactive lymphoid follicles and to invade epithelial structures, forming characteristic lymphoepithelial lesions. Monoclonal proliferation of the lymphoid tissue was demonstrated by the polymerase chain reaction method. The histologic appearance and the demonstration of monoclonality fulfilled the criteria for malignant lymphoma arising from mucosa-associated lymphoid tissue, which is extremely rare in the duodenum.