Diagnostic Approach to Bilious Vomiting in Infants

Initial Evaluation

The American Academy of Pediatrics recommends obtaining an abdominal X-ray immediately as the first diagnostic step for a 5-month-old infant presenting with greenish vomiting and signs of obstruction, followed urgently by an upper GI contrast study if obstruction is confirmed 1, 2
Plain abdominal radiography is the recommended initial imaging study because it can rapidly identify critical signs of intestinal obstruction, including dilated bowel loops, air-fluid levels, and gas distribution patterns that guide subsequent management 3, 1, 2

A "double bubble" sign on the initial X-ray suggests duodenal obstruction 1
A "triple bubble" sign may indicate jejunal atresia 1, 4
Multiple dilated loops with absent/decreased distal gas on the X-ray suggests small bowel obstruction 1
The sensitivity of abdominal X-ray for detecting malrotation is 96%, though false-positives (10-15%) and false-negatives (up to 7%) can occur 1

Greenish vomiting in an infant indicates bile presence, meaning obstruction is distal to the ampulla of Vater, and represents a surgical emergency until proven otherwise 1, 2
The most life-threatening concern is midgut volvulus, which can cause complete intestinal necrosis within hours due to twisting around the superior mesenteric artery 1

Malrotation with midgut volvulus is the most urgent diagnosis to consider in a 5-month-old infant with bilious vomiting 1
Intussusception is a common diagnosis at this age and should be considered in the differential diagnosis 1, 2
Intestinal atresia (jejunal, ileal) is another potential diagnosis in this clinical scenario 1, 4

Intravenous crystalloid resuscitation with isotonic fluids should be initiated simultaneously with imaging 3
Nasogastric tube decompression is recommended to prevent aspiration pneumonia and decompress the proximal bowel 3
NPO status (bowel rest) should be maintained until further notice 3
Urgent pediatric surgical consultation is necessary given the potential for volvulus requiring immediate operative intervention 2

Complete blood count, electrolytes, and renal function tests should be ordered as part of the initial evaluation 3
Low bicarbonate, elevated lactate, and marked leukocytosis may indicate intestinal ischemia 3

Obtain abdominal X-ray immediately, followed by upper GI contrast series if obstruction is confirmed or high clinical suspicion persists despite normal X-ray 1, 2, 3
If upper GI confirms malrotation/volvulus, immediate surgery is necessary 1
If intussusception is suspected, ultrasound may be added, but should not delay definitive imaging 2