Annular pancreas: a case of intermittent duodenal obstruction in an adult

Clinical History

The patient complained of recurrent left flank pain, associated with nausea and vomiting, but no fever. Prior history was not relevant and he did not take any medication. Physical examination revealed tender abdomen, especially in the left flank. Laboratory findings were negative. The attending physician requested an abdominal ultrasound.

Imaging Findings

The abdominal ultrasound showed complete duodenal encasement by pancreatic tissue (Fig. 1 - a, b and c).
This study was complemented by a post-contrast abdominal CT, better visualising the gastric and duodenal dilatation, and the ring of pancreatic tissue surrounding in a circumferential manner the 2nd portion of the duodenum (Fig. 2 -a, b, c and d). Wirsung and common bile duct were normal.

Discussion

Annular pancreas (AP) is a rare congenital anomaly, resulting from malrotation of the pancreatic ventral bud [1].

The pancreas develops from two embryonic buds of the primitive foregut at 5 weeks of gestation: one dorsal and one ventral. In the 6th week of gestation, the duodenum expands and rotates the ventral bud from right to left, causing its fusion with the dorsal bud. The ventral bud forms the uncinate process and inferior portion of the head, while the dorsal bud gives rise to the tail, body and superior portion of the head of the pancreas (see Figure 3).
AP develops due to failure of the ventral bud to rotate with the duodenum, causing its encasement [1].

It can be either complete or incomplete. In complete AP, the pancreatic parenchyma is seen to completely surround the 2nd duodenal portion, whereas in incomplete AP, the annulus does not surround the duodenum completely, showing a 'crocodile jaw' appearance at CT [2].

In children, it may be associated with other congenital anomalies (duodenal atresia, duodenal stenosis, oesophageal atresia, trachea-oesophageal fistula and Down’s syndrome) or cause duodenal obstruction, while in adults, pancreatitis is the usual presentation. However, it can cause duodenal obstruction in adults as well. More common symptoms in adults also include abdominal pain, post-prandial fullness, vomiting and GI bleed from peptic ulcers. In rare cases, biliary obstruction may also be seen [2].
Although annular pancreas in the adult is rare, it may be recognized with increased frequency as a result of more liberal use of pancreatic imaging studies in patients with chronic abdominal pain and suspected chronic pancreatitis [2].

The diagnosis may be suspected if barium studies show narrowing of the duodenum at the level of the major papilla or if duodenal dilatation is seen at ultrasound [1].
At CT, pancreatic tissue is seen to completely or incompletely surround the 2nd portion of the duodenum. Associated duodenal narrowing and dilatation of proximal duodenum may also be seen. Endoscopic retrograde cholangiopancreatography (ERCP) or magnetic resonance cholangiopancreatography (MRCP) can confirm the diagnosis by demonstrating a segment of pancreatic duct encircling the duodenum [1].

Surgery remains the procedure of choice in patients in whom symptoms can be attributed to AP. The goal of surgery is to relieve duodenal or gastric outlet obstruction. The preferred surgical approach is bypass surgery of the annulus, which can be achieved via a duodenoduodenostomy, gastrojejunostomy, or a duodenojejunostomy [3].

Differential Diagnosis List

Final Diagnosis

Annular pancreas

URL:	https://www.eurorad.org/case/11860
DOI:	10.1594/EURORAD/CASE.11860
ISSN:	1563-4086