Mucosal prolapse syndrome-like inflammatory polyp protruding from the appendiceal orifice masquerading as an appendiceal neoplasm: A rare case report.

We describe a case of a mucosal prolapse syndrome (MPS)-like inflammatory polyp protruding from the appendiceal orifice, mimicking an appendiceal neoplasm. A 48-year-old man presented with lower abdominal pain and elevated white blood cell count and C-reactive protein level. Computed tomography showed a swollen appendix with multiple small saccular lesions and periappendiceal fat stranding and small saccular lesions in the ascending colon and cecum. Ultrasonography showed a swollen appendix 25 mm in diameter with multiple saccular structures and a periappendiceal high-echoic area, suggesting appendiceal diverticulitis. Colonoscopy revealed an erythematous lesion protruding from the appendiceal orifice. An ileocecal resection was performed based on a preoperative diagnosis of appendiceal diverticulitis and tumor. Histopathological examination of the appendix showed multiple mucosal herniations with infiltration of inflammatory cells, indicating appendiceal diverticulitis. The tumor was characterized by glandular duct hyperplasia and stromal expansion with smooth muscle hyperplasia and was diagnosed as an inflammatory polyp resembling an MPS lesion. Although several studies have shown the macroscopic and endoscopic appearance of MPS-like inflammatory lesions associated with colonic diverticular disease, this case was the first to present an inflammatory polyp associated with appendiceal diverticulitis in which the lesion protruding from the appendiceal orifice was masquerading as an appendiceal neoplasm.