Based on the radiographic findings, an exploratory laparotomy was performed, which revealed a markedly distended stomach and proximal duodenum. Following mobilization of the duodenum, an annular pancreas, with complete duodenal obstruction, was found. Distally, the small bowel was normal. A duodenoduodenostomy was performed, and she had a normal post- operative course.
Both of the 2 main theories as to how annular pancreas develops involve the left and right ventral buds that normally form the head and neck of the pancreas. Malrotation of the ventral bud that results in pancreatic tissue surrounding the duodenum and failure of the left ventral bud to atrophy have both been proposed.4
Annuli most commonly affect the descending duodenum and may be partially or completely circumferential. Complete duodenal obstruction typically occurs below the level of the ampulla of Vater and presents as bilious vomiting that worsens with subsequent feeding. A partially circumferential presentation can occur later in life or can be asymptomatic.2 The most common abdominal radiographic finding is the double-bubble sign, which is composed of gaseous dilatation of the stomach and proximal duodenum, with a paucity of bowel gas distally. The double-bubble sign may also be observed on prenatal ultrasound as 2 adjacent fluid-filled structures in the fetal upper abdomen and may be accompanied by polyhydramnios. Differential diagnosis of this sign, detected either prenatally or postnatally, includes duodenal atresia, annular pancreas, duodenal stenosis, duodenal webs, and midgut volvulus.5
For neonates with the classic appearance of a double bubble, further radiologic investigation is unnecessary, since all congenital causes of duodenal obstruction require surgery. Surgical repair of annular pancreas with duodenojejunostomy or duodenoduodenostomy can relieve the obstruction and is commonly successful without complication.5
The double-bubble sign is commonly associated with duodenal atresia, but one must keep in mind that it actually represents duodenal obstruction and that other causes of obstruction should be considered. Annular pancreas is an uncommon cause of intestinal obstruction, and patients with this condition usually present in the first year of life. Radiographically, the double-bubble phenomenon is seen in most cases. As with duodenal atresia, annular pancreas is often associated with other congenital anomalies that necessitate thorough examination of these patients. Surgical correction of annular pancreas has a good prognosis.
Annular pancreas. Appl Radiol.