Annular Pancreas

General Considerations

• Rare, congenital anomaly that may not become apparent until adult life
• Pancreas completely (or sometimes incompletely) encircles 2^nd portion of duodenum occasionally obstructing more proximal duodenum
• More commonly affects males
• Pancreas develops from two analogues
  • Larger is dorsal bud which forms body and tail of gland
  • Ventral bud is smaller and forms head of gland as well as parts of the hepatic duct and gallbladder
  • Annular pancreas is believed to develop as a result of abnormalities in migration of the ventral bud such that the two buds join to encircle the duodenum
• Pancreatic duct from the annular portion may drain into the main pancreatic duct or directly into the duodenum

*

Clinical Findings

• Frequently asymptomatic
• May present either in infancy or, more commonly, 4^th-5^th decade of life
  • In newborn, duodenal obstruction with bilious vomiting may be present
    • May be associated with duodenal stenosis or atresia
    • There is a 50% association with other congenital anomalies of involving the heart, trachea and esophagus and malrotation of the intestine
• In adult, there may be
  • Upper abdominal colicky pain
  • Postprandial fullness
  • Vomiting
  • Higher incidence of pancreatitis
  • Peptic ulcers may develop

Imaging Findings

• In newborn, there may be a double bubble sign from dilatation of the stomach and first portion of the duodenum
• In, adult the diagnosis is usually suggested first by CT and can be confirmed with MRCP (magnetic resonance cholangiopancreatography) or ERCP (endoscopic retrograde cholangiopancreatography)
• UGI series    
  • May show extrinsic compression on both lateral and medial walls of the  2^nd portion of duodenum
• CT
  • May be mistaken for thickening of the duodenal wall
    
    
• On MRCP or ERCP, the duct of the annular pancreas usually originates anterior to the duodenum
  
  sweeps posteriorly and opens into the main pancreatic duct or ampulla

Differential Diagnosis

• Pancreatic divisum
  • Failure of the dorsal and ventral pancreatic ducts to fuse resulting in the majority of secretions exiting via the accessory pancreatic duct of Santorini
• Pancreatic neoplasms
• Duplication cyst of the duodenum
• Duodenal atresia

Treatment

• Symptomatic newborns require surgical intervention
• Most symptomatic adults will undergo a surgical bypass of the duodenal obstruction

Complications

• Pancreatitis
• Peptic ulcer disease

Prognosis

• In newborn, except for the possible presence of other congenital anomalies, surgery is usually successful
• Surgery should be completely successful in an adult

Annular Pancreas. Three, contrast-enhanced axial CT images of the abdomen demonstrate the body and head of the pancreas (light blue arrows) completely encircling, but not obstructing, the duodenal loop (red *)
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Annular pancreas in the adult. W Lloyd-Jones, J C Mountain, and K W Warren; Ann Surg. 1972 August; 176(2): 163–170.

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