What's happening here? - Answer

So what we see here is air in the stomach and proximal duodenum but not in the rest of the digestive tract. This is the so-called "Double Bubble" sign.

The double bubble is indicative of obstruction of the duodenum. This can be from intrinsic or extrinsic etiologies. Far and away the most common consideration is duodenal atresia. The differential should include duodenal web and stenosis, annular pancreas, Ladd's bands, malrotation, preduodenal portal vein and duodenal or retroperitoneal tumor.

Considerations for next step - Depends on clinical appearance. Surgery consult, possible upper GI. If the patient has any signs of peritoneal symptoms - Ladd's bands and malrotation with volvulus must be considered and may urgently/emergently go to surgery. If the patient is doing well and surgery may be delayed then may want to do Upper GI to exclude malrotation.

This example - Annular Pancreas. The annular pancreas can present in a variable pattern. The pancreas may actually encircle the duodenum or the ventral pancreas could be incorporated into the wall of the duodenum. According to radiographics, only 10% actually obstruct the duodenum. According to emedicine, it always causes at least some stenosis if not outright atresia like in this case. It is a congenital variant. It can be isolated or associated with other congenital anomalies. In neonates when symptomatic - presents like above with obstructive symptoms such as biliary vomiting or as pancreatitis. In adults - if symptomatic at all - may present with "peptic ulcer" symptoms, pancreatitis, or duodenal obstruction.

Duodenal Atresia

• Extreme end of the spectrum (diaphragm or web, stenosis then atresia)
• Failure of recanalization (favored theory) vs. ischemia
• Death without surgery - due to electrolyte loss and fluid imbalance
• Associated with Trisomy 21 (Down's) - approximately 20-30%
• Anomalies (such as Down's and others) are found in 50% of patients - heart disease, VACTERL, renal anomalies, TE fistula
• If has esophageal atresia as well - stomach will be fluid filled midabdominal mass as it is obstructed on both ends
• Prenatally - polyhydramnios and double bubble on ultrasound.
• Clinically - often have bile stained vomiting
• Stenosis and web - are not complete obstructions so often will have some air beyond the narrowing in the 2nd portion of the duodenum.
• Patients should do well after corrective surgery.

references: http://radiology.rsnajnls.org/cgi/content/full/220/2/463 , http://radiographics.rsnajnls.org/cgi/content/full/26/3/715 , emedicine.com and Primer of Diagnostic Imaging by Weissleder et al.