A 65-year-old man presented with intermittent abdominal distension for 1 month, along with absence of passage of stool and gas for 3 days. Physical examination revealed abdominal distention, mild tenderness in the lower abdomen, and hypoactive bowel sounds. Abdominal CT revealed a 4-cm mass in the sigmoid colon, causing lumen stenosis; the adjacent mesentery and omentum exhibited nodular hyperplasia and swelling, with invasive involvement around the left ureter (A). Advanced colon cancer was highly suspected, and an emergency transverse colostomy was performed.

Water exchange (WE) and cap-assisted colonoscopy separately have been shown to reduce pain during insertion in unsedated patients. We hypothesized that compared with WE, WE cap-assisted colonoscopy (WECAC) could significantly lower real-time maximum insertion pain (RTMIP).