We experienced a case involving a transomental hernia that developed shortly after laparoscopic sigmoidectomy. A transomental hernia is a rare complication of surgery, and this is the first report of a transomental hernia that developed after laparoscopic colorectal surgery.
Transomental hernias are particularly rare, constituting only 1% to 4% of all internal hernias; only 24 cases have been reported in the English-language literature . The pathogenesis of a transomental hernia involves the development of a congenital defect of the omentum and omental fragility caused by emaciation or atrophy of the omentum secondary to aging, oral steroids, trauma, surgery, or inflammation [3, 4]. In the present case, no congenital omental defect was found, and the omentum was not dissected or roughly manipulated during the initial laparoscopic surgery. Additionally, factors including (1) omentum was relatively thin and transparent partially, and (2) no obvious omental adhesions to abdominal wall and adjunct organs were observed at the re-laparotomy, led us to make a conclusion that initial surgery had no direct causal effect with the occurrence of transomental hernia, however, could have influenced the secondary development of ometal fragility, followed by the formation of a hernial defect.
The short-term benefits and safety of laparoscopic surgery for colorectal cancer have already been demonstrated; however, a certain number of patients could develop postoperative complications [6, 7]. Although the incidence of an internal hernia after laparoscopic colorectal surgery is low (0.65%) , most internal hernias are caused by a previous surgical procedure . Left-sided colonic resection accounts the vast majority of primary laparoscopic surgeries that result in internal hernias. Most internal hernias are transmesocolic . One plausible cause is the formation of a relatively large defect of the mesocolon secondary to the procedure. Most such large mesocolic defects are not easily repaired because of the technical difficulty. Postoperative internal hernias frequently occur 4 months after surgery . In contrast, the internal hernia in the present case occurred just 12 days after surgery. The reason for the short time to onset in our case is unknown; however, two hypotheses are reduction of intra-abdominal adhesions with laparoscopic surgery and increased intra-abdominal pressure with early mobilization as part of an enhanced recovery program.
Seven types of internal hernias have been described: paraduodenal, pericecal, foramen of Winslow, intersigmoid, transmesenteric, transomental, and retroanastomotic hernias. Transomental hernias are the rarest type . Yamaguchi  classified transomental hernias as type A (peritoneal cavity → greater omentum → peritoneal cavity), B (peritoneal cavity → omental bursa → peritoneal cavity), or C (peritoneal cavity → omental bursa). Type A is the most the common, and the hernia in the present case was also type A.
In general, the preoperative diagnosis of an internal hernia itself is not challenging . Characteristic CT findings and the patient’s history allowed us to diagnose the internal hernia in this case; however, we could not identify the specific pathogenesis. Despite the high mortality of transomental hernias (30%) [2, 3], the definitive diagnosis is usually established intraoperatively, as in our case . Ito et al.  recently reported the clinical utility of the CT finding of displacement of the transverse colon posterior to obstructed intestinal loops, which distinguishes transomental hernia from other types of small bowel obstruction.
In this case, we resected the part of the omentum that formed the defect to eliminate the potential for future bowel incarceration. Korn et al.  reported complete omental resection in a patient with Swiss cheese omentum containing multiple defects of varying size. In contrast, Cao et al.  reported the closure of multiple mesenteric defects to preserve the omentum and thus prevent adhesional bowel obstruction.
A transomental hernia is a rare cause of small bowel obstruction after intestinal surgery. Diagnosis of an internal hernia by imaging findings is not difficult, but preoperative identification of the cause as a transomental hernia is challenging. When patients with an internal hernia are encountered, the decision-making process should be immediately implemented and based on surgical exploration, which is important to prevent further morbidity and mortality. Clinicians should be aware of the possibility of a transomental hernia.