Transmesenteric internal hernia: an unexpected adverse event induced by colonoscopy.

Transmesenteric internal hernia is an uncommon cause of small bowel obstruction that occurs when small bowel loops protrude through a mesenteric defect into the abdominal cavity. Herein, we present an unexpected case of colonoscopy-induced transmesenteric internal hernia. An 81-year-old male patient presenting with intermittent hematochezia and constipation had undergone a laparoscopic left nephrectomy for ureteral cancer. A colonoscopy was performed to identify the etiology of his symptoms. He complained of severe abdominal pain 2 h after the examination despite uneventful endoscopic procedures, including cold snare polypectomy. Contrast-enhanced computed tomography revealed a strangulated small bowel obstruction with a closed-loop formation outside the descending colon. The small bowel loop was incarcerated into the left retroperitoneal space. Emergency laparotomy detected small bowel loops that prolapsed into the nephrectomy pedicle via a descending mesenteric defect, developed during the laparoscopic left nephrectomy. The incarcerated small bowel was detached from the hernia and returned to its normal position, and the mesenteric defect was closed. He demonstrated an uneventful postoperative course, with no internal hernia recurrence after discharge. This case indicates the risk of transmesenteric internal hernia through inadvertently created mesenteric defects should be borne in mind, especially when performing colonoscopies in patients who underwent laparoscopic nephrectomies.