Misconstruction of the RNY conguration, termed a Roux-en-O, is rare and an underreported outcome of bariatric surgery with potentially devastating consequences for patients [42]. Improper construction occurs when the biliopan­creatic limb is mistakenly anastomosed to the gastric pouch resulting in a closed “O” loop (Fig. 16.1). Patients typically present with abdominal pain, biliary emesis, esophagitis, severe dehydration, and nutritional malnutrition. The nonspecic nature of these symptoms along with altered surgical anatomy can pose diagnos­tic challenges and often delay diagnosis [43]. Diagnostic tools such as endoscopy, CT with contrast, and swallow studies may fail to identify the incorrect conguration especially when intes­tinal dilation masks the actual pathology [44]. Indicators on CT scans suggesting a Roux-en-O conguration include dilation of the proximal small bowel between the gastric pouch and gas­tric remnant with decompressed distal small bowel and colon. Notably, the hepatobiliary imi­nodiacetic acid (HIDA) scan aids in the diagnosis of this misconguration when the radiotracer moves into the duodenum and then backows into the esophagus [40, 41]. Once a diagnosis has been conrmed, surgery is often required to cor­rect the anatomy.