This newborn's presentation of bilious vomiting and feeding intolerance, combined with the radiographic findings above, is consistent with midgut obstruction secondary to volvulus. Intestinal malrotation results in midgut obstruction and volvulus, which may also lead to gut ischemia in severe cases.
During the course of development of the GI tract, the midgut first herniates through the umbilical ring at 6 weeks gestation. Subsequently, at 10-11 weeks gestation, the midgut rotates 270 degrees counterclockwise around the superior mesenteric artery while returning into the abdominal cavity. Abnormal progression of this embryologic sequence can lead to mechanical obstruction of the intestines as well as compromised intestinal blood supply secondary to the intestines twisting about themselves in an abnormal conformation.
Kimura and Loening-Baucke discuss the diagnosis and management of an infant with bilious vomiting. Bilious vomiting in an infant should be considered diagnostic of midgut malrotation with volvulus until proven otherwise. Initial management includes placement of an NG/OG tube to decompress the stomach, followed by physical exam and radiographs of the abdomen. Any suggestion at compromised blood flow to the bowel classifies this condition as a surgical emergency necessitating urgent operative intervention.
Lampl et al. discuss the radiographic evaluation of intestinal malrotation and volvulus. They state that upper GI contrast radiography remains the most efficient means of diagnosing this condition. Specific elements to look for include: signs of duodenal obstruction, positioning of the ligament of Treitz, and abnormal location of the cecum.
Figure A shows an upper GI contrast radiograph that demonstrates obstruction of the duodenum with classic "bird-beak" appearance. Illustration A is a graphical representation of the mechanism of malrotation and midgut volvulus. Illustration B summarizes normal intestinal rotation in a fetus.
Answer 1: Failure to recanalize the lumen of the duodenum is the mechanism of duodenal atresia; it classically presents as a "double bubble" sign on contrast radiographs. It would be easy to confuse this image with duodenal atresia were it not for the history which included duodenojejunal displacement.
Answer 2: Hypertrophy of the muscularis externa at the pylorus describes congenital pyloric stenosis, which presents with nonbilious projectile vomiting; it is most commonly seen in first-born males with a palpable olive like mass in the abdomen.
Answer 3: Failed fusion of lateral body folds is the mechanism of gastroschisis, where intestines extrude through the umbilical ring but are not covered by peritoneum.
Answer 5: Failed fusion of the dorsal and ventral pancreatic buds describes pancreas divisum; the majority of cases are asymptomatic and only discovered incidentally. The radiograph in this question could easily also be annular pancreas were it not for the history given.
Conclusion: Sometimes the double bubble sign of duodenal atresia can seem to appear in cases of malrotation of the gut and annular pancreas. It is important to assume the patient suffers from malrotation of the gut and rule that out given it has the most serious complications if left uncorrected. Use the history to determine the best answer.
Kimura K, Loening-Baucke V. Bilious vomiting in the newborn: rapid diagnosis of intestinal obstruction. Am Fam Physician. 2000 May 1;61(9):2791-8.
PMID:10821158 (Link to Abstract)
Lampl B, Levin TL, Berdon WE, Cowles RA. Malrotation and midgut volvulus: a historical review and current controversies in diagnosis and management. Pediatr Radiol. 2009 Apr;39(4):359-66. doi: 10.1007/s00247-009-1168-y. Epub 2009 Feb 25.
PMID:19241073 (Link to Abstract)
USMLE World Step 1 QBank Question #318. Copyright © USMLEWorld, LLC 2012