The rectal tonsil: a reactive lymphoid proliferation that may mimic lymphoma.

The rectal tonsil (RT), a localized reactive proliferation of lymphoid tissue occurring in the rectum, can cause diagnostic difficulty; and awareness of this entity can prevent a misdiagnosis of lymphoma. A clinicopathologic analysis of 11 cases of RT was performed to determine the features that can aid in the recognition of this entity. The patients (6 males and 5 females) were middle-aged adults, except for 1 case affecting a young boy (age range, 1 to 62 y; mean, 49 y). All presented with either rectal bleeding or abdominal pain, or had the lesion found on routine screening. Endoscopic descriptions, available in all cases, reported a raised, polypoid lesion in 8 cases, a nodule in 2 cases, and a "mass" in 1 case. Histologically, all cases were composed of a lymphoid proliferation involving the lamina propria or submucosa. Lymphoid follicles could be identified in all cases, although some were difficult to appreciate without immunostains for follicular dendritic cells. Five cases showed overlying cryptitis and mild architectural distortion, but no cases showed crypt obliteration or crypt abscesses. Intraepithelial lymphocytes were present in 9 cases, and 5 cases showed nondestructive lymphoepithelial lesions. During a mean follow-up of 5.8 years, none showed a recurrence or developed lymphoma. In conclusion, RT, with its distinctive features, is an important entity to recognize. Familiarity with the range of histologic features characteristic of the RT is critical in avoiding misinterpretation as lymphoma.