Post-gastric bypass-associated internal hernia is a well-described complication associated with laparoscopic Roux-en-Y bypass surgery. The incidence of internal hernia in this population ranges from around 2% for those who had their mesenteric defect closed vs. 6% if the mesenteric defect was not closed. Different possible hernia sites include Petersen’s space, Jejunojejunostomy mesenteric defect, and the transverse mesocolon defect. Timely identification of internal hernias is extremely important, as they can become obstructed or incarcerated, leading to necrosis. Having a structured approach to CT reporting has been shown to improve diagnostic accuracy. We report a case of a 65-year-old woman who presented to the emergency department and was later diagnosed intraoperatively with an internal hernia after contrast-enhanced CT identified key diagnostic signs. Additionally, we will review other important signs not identified in this case that can be used to help healthcare providers identify internal hernia more accurately.

Case information: A 65-year-old female with a past medical history of gastric bypass, abdominoplasty, and cholecystectomy, with all surgeries occurring around 15 years ago, presents to the emergency department for severe cramping abdominal pain, nausea, and vomiting. Vital signs are stable; there is no leukocytosis, and a CT without contrast is performed due to deferral of contrast. CT demonstrates mesenteric edema and nonspecific changes. Her pain resolves, and she is again able to tolerate food. A diagnosis of Dumping syndrome was made, and she was discharged.

Two days later, she returns to the emergency department with similar symptoms. Metabolic panel shows elevated BUN and creatinine along with a mild anion gap of 18. Liver function tests, lipase, and magnesium are within normal limits. A CT with contrast is performed, and bariatric surgery is consulted.

Discussion and clinical findings: Contrast-enhanced CT demonstrated prior Roux-en-Y bypass, swirling and edema of the mesentery with a questionable transition point of the biliary limb in the midline upper abdomen. Signs of post-laparoscopic Roux-en-Y gastric bypass-associated internal hernia on CT include: (1) swirl sign, (2) small-bowel obstruction, (3) clustered loops, (4) mushroom sign, (5) hurricane eye sign, (6) small bowel behind the superior mesenteric artery, (7) right-sided anastomosis, (8) enlarged nodes, (9) venous congestion, and (10) mesenteric edema. The presence of the swirl sign is considered to have the highest combination of sensitivity and specificity for detecting a post-gastric bypass internal hernia on CT.