A 36-year-old female presented to the emergency department with intense upper abdominal pain. Her pain started 5 hours ago, was progressively worsening with intermittent peaks and increased after water ingestion. Previous history included Roux-en-Y gastric bypass (RYGB) 2 years ago and laparoscopic closure of mesenterial defects (Petersen and jejunojejunostomy) one year ago.
Contrast-enhanced CT of the abdomen in portal venous phase with positive oral contrast was performed. No distended bowel loops were present, the jejunojejunostomy was located in the normal location in the left middle abdomen and oral contrast had passed to the distal ileal loops. The superior mesenteric vein (SMV) had a decreased calibre with a beaked appearance (“SMV beaking”). (Figure 1, arrowhead)
A small bowel loop had a stretched course posterior to the superior mesenteric artery (SMA) branches (“small bowel behind SMA sign”). (Figure 2, arrowhead)
A swirled appearance of the mesenteric vessels was present in the anterolateral left middle abdomen at the level of the jejunojejunostomy (“swirl sign”) with slightly enlarged lymph nodes and mesenterial infiltration in this region. (Video 1)
There were clustered small-bowel loops in the anterolateral left middle abdomen, near the jejunojejunostomy (“clustered loops sign”). These findings were not present at the previous abdominal MRI of one year ago. (Figure 3, circle) No other signs of internal herniation were present.
These findings indicated internal herniation after RYGB without significant bowel obstruction. The location of the clustered loops and “swirl sign” near the jejunojejunostomy and absence of “hooking intestine sign” (Figure 4) suggested an internal herniation through the jejunojejunostomy mesenteric defect. These findings were confirmed on laparoscopy.
Background and clinical perspective:
In Roux-en-Y gastric bypass (RYGB) a gastric pouch is connected to an alimentary limb, which is joined to a biliary limb at the jejunojejunostomy. Internal herniation (IH) typically occurs after significant weight loss, with upper abdominal pain and signs of bowel obstruction (SBO). However, signs of SBO may be absent and pain may be intermittent. 
In retrocolic RYGB, three mesenteric defects are created: a transmesocolic defect, a defect at the jejunojejunostomy between the mesentery of the alimentary limb and biliopancreatic limb and the Petersen defect between the mesentery of the alimentary limb and transverse mesocolon. Antecolic RYGB lacks the transmesocolic defect and has a lower risk of IH. Closure of mesenteric defects reduces but does not eliminate the risk of IH. Laparoscopic RYGB induced less formation of adhesions and has been shown increased the risk of IH compared to open RYGB. 
CT is the first-line non-invasive investigation in suspected IH, at least 13 signs associated with IH have been described. [2, 3, 5]
Although SBO combined with a “swirl sign” has the highest diagnostic accuracy, no single sign is required for diagnosis. As demonstrated in this case, a presentation without signs of SBO could be missed when not evaluating all signs. 
Transmesocolic IH is the most frequent type of IH after retrocolic LRYGB and can be identified by clustered bowel loops in the left upper quadrant posterior to the excluded stomach and a transition point at the level of the transverse mesocolon in case of SBO, best appreciated on sagittal images. [4, 6]
IH through the Petersen and the jejunojejunostomy mesenteric defect are more difficult to distinguish. The “hooking intestine sign” was highly specific for Petersen hernia in a recent study by Yamashita et al , this sign results from bowel loops herniating through the Petersen defect between the mesentery of the alimentary limb and transverse mesocolon.  Clustered loops and a “swirl sign” near the jejunojejunostomy are suggestive of IH at the jejunojejunostomy mesenteric defect, these clustered loops can be located either in the right or left middle abdomen. [4, 6]
Outcome: therapeutic options, prognosis, impact of imaging on therapy planning
Treatment consists surgical hernia reduction and closure of mesenteric defect(s). Prognosis is depended on the viability of the herniated bowel loops.
Take-Home Message / Teaching Points
Internal herniation after RYGB can be a challenging diagnosis. However, this case report illustrates that evaluating all signs and comparing with previous imaging allows diagnosis and subtyping of IH, even in the absence of signs of SBO in a patient with a history of closure of mesenteric defects.
Written informed patient consent for publication has been obtained.
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