The presentation can be widely varied from severe acute abdominal pain requiring an emergency management to chronic intermittent abdominal pain requiring a conservative approach and semi elective laparoscopic exploration when needed [8]. Patients with Petersen’s hernia may have pain that could sometimes be ameliorated by adopting the hand and knee positions [11]. Considering the variability in the symptoms, the role of imaging assumes prime importance, especially in patients without any obvious signs of severe intestinal obstruction or peritonitis [8].

X-ray can identify intestinal obstruction, but most patients with internal hernias (IH) do not have evident signs of small bowel obstruction on plain films making contrast studies or CT necessary [11]. A CT scan can help make the diagnosis of an IH, especially when a mesenteric swirl sign is present, which is defined as a twisting pattern of mesenteric vessels indicating midgut volvulus. The other CT findings that can be seen are mushroom sign, hurricane eye, small bowel obstruction, clustered loops in the left hypochondrium, small bowel behind the superior mesenteric artery(SMA), right sided location of J-J anastomosis, dilated remnant stomach etc [12].

The sensitivity of the swirl sign varies between 60 and 100 % and specificity between 63 and 94 % [12–14]. The sensitivity and specificity of the other signs has a larger inter-observer variability and also lacks sensitivity. This variability could be related to the experience of the radiologist, as shown by Al-Mansour et al where a retrospective review by a board certified radiologist showed positive findings in a few CT films which were earlier reported normal [8]. This stresses the need for an experienced radiologist and also the need for surgeons to be familiar with the cross sectional imaging of these patients.

Marchini et al noticed two signs specific to Petersen’s hernia with small bowel obstruction [15]. A sac like cluster of small bowel loops displaced towards the left mid-abdominal wall, coming from behind the Roux limb and in front of the angle of Treitz, and a horizontal course of engorged superior mesenteric vessels towards the left abdominal wall.

The issue of mesenteric defect closure has been discussed in detail earlier in chapter 10 on the technique of RYGB. Petersen’s hernia has been more commonly encountered in patients with mesenteric closure only. While the incidence of overall IH did not change with Petersens defect closure, the rates of Petersens hernia has actually reduced from 84 to 33 % [8]. Rodriguez et al reported that with experience and change of technique, the incidence of IH can be reduced significantly [11]. From not closing the Petersens defect and dividing the mesentery until the base with closure of the defect with small bites to routine closure of the Petersens defect and avoiding the mesenteric division and thick interrupted bites on the mesentry reduced the IH incidence from 15.5 to 1.1 %. This highlights the importance of good mesenteric closure in preventing internal hernias.

The data is divergent about the incidence of Petersens and mesenteric hernias. Koppmann et al depicted a higher rate of Petersen hernia(56 %) while Ianelli et al believes mesenteric hernias to be more prone with gravity facilitating the intestine projection into the space with lower position [16, 17]. Karcz et al had noted no significant difference in the incidence of both the types of hernias [18]. It was also noted that biliopancreatic limb was the most common to herniate and in the direction of left-right. In cases of alimentary limb or the common channel the direction was opposite. It was also interesting to note that following BPD-DS, the hernias were seen only at the Petersens and not the mesenteric defect. A classification system called SDL(Space-Direction-Limb) classification system has been proposed to help in clinical understanding and communication of information and possible evaluation of severity [18]. Al-Mansour et a reported 3 cases of bowel gangrene with Petersens hernia. This was in patients in whom only the JJ defect was closed and not the Petersens [8].