Internal hernias are an uncommon cause of small bowel obstruction. They develop when an abdominal viscera, usually the small bowel, passes through a peritoneal orifice (either congenital or acquired), but remains in the peritoneal cavity. Depending on the location of the peritoneal aperture and the herniated viscera, different types of hernia have been described, but the most common are left-paraduodenal and transmesenteric hernias.
In the left paraduodenal hernia the small bowel invaginates through a congenital defect in the descendent mesocolon to the fossa of Landzert. Transmesenteric hernias occur due either to a congenital or acquired defect in the small bowel mesentery or transverse mesocolon. The increasing frequency of surgical procedures in which a Roux-en-Y anastomosis is performed is raising the incidence of this last type of internal hernia.
The risk of strangulation of the sac contents, especially in transmesenteric hernias, is high, and so a prompt diagnosis istherefore crucial.
Clinical diagnosis is challenging. Symptoms are nonspecific and sometimes intermittent. During asymptomatic intervals no abnormality might be found.
Imaging studies, especially CT, are helpful in establishing a preoperative diagnosis of the presence, type and possible complications. CT criteria of internal hernia include clustering of small bowel loops, stretched and engorged mesenteric vessels and displacement of other bowel segments with signs of intestinal obstruction. Fixed small bowel loops adjacent to the abdominal wall, the lack of omental fat overlying the herniated bowel and central displacement of the colon have been proposed as distinctive features of transmesenteric hernia. Superimposed signs of volvulus and ischaemia are frequently found as complications of this type of internal hernia.
