A Case of Mucosa-Associated Lymphoid Tissue Lymphoma of the Sigmoid Colon Presenting as a Semipedunculated Polyp
A 54-year-old man visited Daegu Catholic University Hospital after a screening colonoscopy that revealed a sigmoid colon polyp that was diagnosed pathologically as a tubular adenoma. He denied other symptoms such as abdominal pain, weight loss, fever, general weakness, loss of appetite, or hematochezia. His blood pressure was 106/64 mm Hg, pulse rate 73 beats per minute, respiratory rate 20 breaths per minute, and body temperature 36.7℃. His consciousness was clear, and no lymphadenopathy was evident in the head and neck, axillary, or inguinal region. Abdominal examination revealed no tenderness or rebound tenderness. Bowel sounds were normal, and the liver and spleen were not palpable. The laboratory findings were as follows: white blood cells, 11,400/mm3 (neutrophils 81.8%, eosinophils 0.4%, lymphocytes 12.4%); hemoglobin, 13.4 g/dL; and platelet count, 202,000/mm3. The blood chemistry test showed the following results: aspartate aminotransferase, 16 IU/L; alanine aminotransferase, 21 IU/L; total bilirubin, 0.6 mg/dL; alkaline phosphatase, 129 IU/L; total protein, 6.5 g/dL; albumin, 4.4 g/dL; blood urea nitrogen, 12.2 mg/dL; creatinine, 0.9, mg/dL; Na, 139 mEq/L; K, 3.4 mEq/L; and Cl, 98 mEq/L. The serum carcinoembryonic antigen level was 2.69 ng/mL, which was within the reference range.\nColonoscopy revealed a semipedunculated polyp, approximately 2 cm in size, in the sigmoid colon. The surface of the polyp showed redness and nodularity (). In private clinics, the tumor was diagnosed as a tubular adenoma; however, a diagnosis of submucosal tumor was not completely ruled out. We performed EMR by en bloc resection of the polyp with a flex knife and a snare after injecting a glycerin solution into the submucosa ().\nResected specimens histologically showed lymphoepithelial lesions with diffuse proliferation of atypical lymphocytes, which immunohistochemically stained positively for CD20, CD5, and Bcl-6, but negatively for CD3, Bcl-2, and cyclin D1. In addition, the Ki-67 labeling index was 10% to 20%. These findings were compatible with low-grade B-cell MALT lymphoma ().\nThere was no evidence of lymph node metastasis or involvement of any other organ, except for a gallstone, in the thoracic and abdominal computed tomography performed for staging. According to the Ann Arbor staging system, the tumor was stage IE.\nThe resected lesion was replaced with normal mucosa on sigmoidoscopy 2 months after the EMR (). He has been free of disease during 10 months of follow-up.