Introduction: A duplication cyst in the alimentary tract is a rare congenital anomaly that most often occurs in the small bowel and rarely occurs in the colon. Most cases in the small bowel are diagnosed at childhood due to complications or symptoms caused by the duplication cyst. However, duplication cysts in the colon are often asymptomatic, despite resulting in rare complications, such as obstruction, infection, and inflammation. Thus, duplication cysts in the colon can be detected incidentally through imaging studies or during a colonoscopy, causing them to possibly be misdiagnosed as a submucosal tumor of the colon.
Case Report: We present a case of a duplication cyst of the sigmoid colon, which was preoperatively misdiagnosed as a submucosal tumor. A 64-year-old male was referred for treatment of the submucosal mass of the sigmoid colon. A large round submucosal mass was found in the sigmoid colon during colonoscopy, and computed tomography revealed an approximately 4 cm homogeneous enhancing mass of the sigmoid colon without evidence of lymphadenopathy. With a presumed diagnosis of submucosal tumor, laparoscopic anterior resection was performed. However, histologic examination showed that the mass was consistent with a duplication cyst in the sigmoid colon.
Conclusion: This case represents an unusual case of a duplication cyst in the sigmoid colon, which could not be preoperatively diagnosed. Although its preoperative diagnosis is difficult given its rarity, a duplication cyst can be considered one of the differential diagnoses of a submucosal colon mass.