Introduction: A variety of submucosal lesions can be found in the colon and are often an incidental finding. Most are benign, including lipomas, leiomyomas, and lymphoid aggregates. Malignant causes also exist, including neuroendocrine tumors and metastatic lesions. Soft lesions generally represent lipomas, confirmed by a positive “pillow sign.” However, accurate diagnosis of a firm submucosal lesion requires histological assessment. We present a case of a rare benign firm submucosal lesion discovered on colonoscopy.

Case report: A 53-year-old woman underwent gastroscopy and colonoscopy for investigation of iron deficiency anemia. She had no history of weight loss and a normal bowel habit. Gastroscopy was unremarkable. At colonoscopy, one 3-mm firm submucosal nodule was found in the proximal ascending colon (Fig. 1).This was resected en bloc using a cold polypectomy technique. No other abnormalities were found. Histology showed a well-defined lesion in the mucosa and submucosa composed of abundant histiocytes admixed with small numbers of lymphocytes, plasma cells, neutrophils, and rare eosinophils. Many of the histiocytes contained characteristic Michaelis–Gutmann bodies, which were periodic acid–Schiff positive (Fig. 1).

Conclusion: Malakoplakia is a rare granulomatous disease that can involve many organ systems. The exact pathogenesis is poorly understood but is thought to be related to impaired macrophage ability to phagocytose bacteria, leading to formation of pathognomonic Michaelis–Gutmann bodies.1 It is mostly seen in the genitourinary tract but can also occur rarely in the gastrointestinal tract. Malakoplakia in the genitourinary tract has been reported to coexist with urothelial carcinoma, MALT lymphoma, and prostate cancer.1,2 However, no association between malakoplakia and malignancy of the colon has been found.3 It is generally thought to be a benign condition, with no specific follow-up required in the gastrointestinal tract.