Low-Grade Cystic Mucinous Neoplasm of the Colon: A New Entity? Case Report and Review of Literature

Low-grade cystic mucinous neoplasm of the sigmoid colon has never been previously reported and a classification for such a tumor does not currently exist. Here, we present a case of low-grade cystic mucinous neoplasm of the sigmoid colon and discuss the differential diagnosis especially as it relates to clinical management. Our case is a 68-year-old male who presented with anemia and a history of a lower gastrointestinal tract bleed. He denied abdominal pain and weight loss. A colonoscopy was done for further investigation, and he was found to have a 4-cm nonbleeding submucosal mass in the descending colon. Mucosal biopsies were inconclusive. An MRI of the abdomen and pelvis showed a 7.4 × 4.6 cm complex fluid collection involving the mid sigmoid colon with extensive diverticulosis and wall thickening of the sigmoid colon. The differential diagnosis included sequela of diverticulitis vs. neoplasm. Due to the increased risk of obstruction or perforation, a sigmoid resection was recommended. The patient underwent a robotic low anterior resection (LAR). Histological examination demonstrated a cystic mucinous neoplasm filled with acellular mucin and lined by pseudostratified columnar cells with low-grade dysplasia. The tumor involved the muscularis propria and subserosa. Cystic mucinous neoplasm of the colon is not currently recognized among tumors of the colon. Its malignant potential is uncertain. This is the first case report describing a cystic mucinous neoplasm of the sigmoid colon. Recognition of this unusual tumor can help to guide appropriate clinical management and guide further treatment.