What causes the double bubble sign on the neonatal abdominal radiograph and prenatal ultrasound?
Let me know in the comments.
Click to reveal the answer
Answer:
The double bubble sign is two gas-filled (or, antenatally, fluid-filled) upper abdominal structures: the distended stomach on the left and the dilated proximal duodenal bulb on the right, separated by the pylorus, with little or no gas beyond. It indicates complete or near-complete duodenal obstruction, most often duodenal atresia, and is seen on the neonatal abdominal radiograph and from the second trimester on prenatal ultrasound. The single most important observation is the distal bowel gas pattern. A completely gasless abdomen distal to the second bubble indicates atresia; gas beyond it points instead to duodenal stenosis, a fenestrated web, annular pancreas, or, critically, malrotation with midgut volvulus or Ladd bands, which is a surgical emergency and must be excluded by an upper GI study. Roughly 25-40% of infants with duodenal atresia have trisomy 21. Duodenal atresia does not always produce the sign: gas can bypass the atretic segment through an anomalous bifid biliary or pancreatic duct.
Why is it called so?
Two rounded gas or fluid collections sit side by side in the upper abdomen like a pair of bubbles.
Pathophysiology
Duodenal atresia arises from failure of recanalisation of the duodenal lumen around the eighth to tenth week of gestation, most commonly just distal to the ampulla. Swallowed air or amniotic fluid distends the stomach and the duodenum proximal to the obstruction, while nothing passes beyond it, so the two dilated segments are outlined against the airless remainder of the abdomen and the intervening pylorus separates them into discrete bubbles. Extrinsic causes such as annular pancreas, Ladd bands or midgut volvulus produce the same appearance by obstructing the same segment from outside, which is why the sign identifies the level of obstruction but not its cause.
Alternative names: Double bubble appearance
Other associated named signs: Triple bubble sign of jejunal atresia, whirlpool sign and corkscrew sign of midgut volvulus, and the gasless abdomen
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
Improve Content And Help Your Colleagues!
Found an error in the post? Please let us know using our contact page and we will update it with due credits!
If you wish to contribute radiological images for this case (or any other article on the website), you can submit them here and you will be duly credited: Submit radiology case