A case of diverticulum of the appendiceal base resembling a submucosal tumor of the cecum under colonoscopy: a hitherto undescribed lesion

Diverticulosis of the appendix is an uncommon clinical entity, and a preoperative diagnosis is often difficult. Herein we report an unusual case of appendiceal diverticulosis. A 72-year-old male was referred to our hospital to examine the cause of hematochezia. A colonoscopy study showed a protruding lesion resembling a submucosal tumor (SMT), approximately 20 mm in diameter, at the site around the appendiceal orifice of the cecum. An abdominal computed tomography and magnetic resonance imaging showed a cystic lesion at the appendiceal base. The lesion was clinically diagnosed as a cystic tumor of the appendix, but the possibility of a malignant tumor could not be excluded. Therefore, a laparoscopic ileocecal resection with lymph node dissection was performed. The pathological examination of the resected specimen revealed that the lesion was a diverticulum (pseudodiverticulum) occurring solitarily at the appendiceal base, in which the mucosal layer of the appendix was invaginated into the submucosa of the adjacent cecum, thus forming an SMT-like lesion. To our knowledge, this is the first case report in the English literature showing that an appendiceal diverticulum can manifest as an SMT-like lesion in the cecum. This condition should be recognized as a differential diagnosis for such lesions.