Extranodal Marginal Zone Lymphoma Presenting within the Meckel Diverticulum as Diverticulitis: A Case Report.

Meckel diverticulum is the most common congenital defect of the gastrointestinal tract. It can be asymptomatic or mimic appendicitis and may be complicated by bleeding, diverticulitis, obstruction, and, rarely, neoplasia. We report the first case of extranodal marginal zone lymphoma occupying a Meckel diverticulum. A 44-year-old man with history of colonic diverticulitis presented to the emergency department for evaluation of acute abdominal pain. Radiography showed enteric obstruction, prompting diagnostic laparoscopy. Above the level of mid-ileum an intact Meckel diverticulum was identified. Microscopy showed extensive infiltration of sheets of small lymphocytes with abundant cytoplasm (monocytoid B-cells) prominently in submucosa and focally transmural involving serosal adipose tissue with multiple reactive germinal centers. The immunostains showed positivity for CD20, BCL-2, and CD43 (weak) and negativity for CD3, CD5, BCL-1, CD10, and BCL-6 in monocytoid B-cells. Fluorescence in situ hybridization studies revealed API2-MALT1 fusion signals consistent with t(11;18)(q21;q21), which confirmed the diagnosis of extranodal marginal zone lymphoma, also known as mucosa associated lymphoid tissue lymphoma.