Annular Pancreas

Annular pancreas is the second most common congenital pancreatic anomaly (after pancreas divisum), occurring in 1 in 2000 people. Its embryogenesis is unclear, but the end result is pancreatic tissue surrounding the second portion of the duodenum. This may be partial or complete.

Annular pancreas can be extramural or intramural. In the extramural type, the ventral pancreatic duct encircles the duodenum to join the main pancreatic duct. In the intramural type, the pancreatic tissue is intermingled with the duodenal wall muscle and small pancreatic ducts drain directly into the duodenum.

Patients with extramural annular pancreas can present with high gastrointestinal obstruction, sometimes with pancreatitis. Patients with intramural annular pancreas can present with symptoms of duodenal ulceration.

Contrast fluoroscopy can suggest the diagnosis by revealing narrowing at the level of the major papilla. ERCP or MRCP can show the duct of Wirsung encircling the duodenum in the patient with extramural annular pancreas. Cross sectional imaging will show pancreatic tissue around the second portion of the duodenum, as shown above in two patients with annular pancreas.

References

• Johnston DW. Annular pancreas: a new classification and clinical observations. Can J Surg. 1978 May;21(3):241-4.
• Mortelé KJ, Rocha TC, Streeter JL, Taylor AJ. Multimodality imaging of pancreatic and biliary congenital anomalies. Radiographics. 2006 May-Jun;26(3):715-31.
• To'o KJ, Raman SS, Yu NC, Kim YJ, Crawford T, Kadell BM, Lu DS. Pancreatic and peripancreatic diseases mimicking primary pancreatic neoplasia. Radiographics. 2005 Jul-Aug;25(4):949-65.