Annular Pancreas

Excerpt

Annular pancreas (AP) is a rare congenital anomaly characterized by partial or complete circumferential encasement of the second part of the duodenum by a band of pancreatic tissue during embryogenesis. It is usually located above the papilla of Vater in approximately 85% of diagnosed cases. Older studies have reported the prevalence of AP in three of 20,000 autopsies and three of 24,519 surgical cases. With the advent of newer and improved diagnostic modalities, this condition is being recognized more frequently. Many individuals with this anomaly remain asymptomatic throughout their lifetime and are often diagnosed incidentally on imaging or during autopsies. However, a fraction of patients with AP tends to present with clinical manifestations either early in life or during adulthood usually between 20 and 50 years of age.

Based on the morphologic distribution of pancreatic tissue, AP has been classified into a complete or incomplete type. Complete type AP shows pancreatic parenchyma or annular duct completely encircling the second part of the duodenum confirmed by macroscopic inspection, and incomplete type AP demonstrates partial circumferential encasement of the duodenum by pancreatic tissue confirmed by endoscopic retrograde cholangiopancreatography (ERCP) or surgical evaluation. The annular pancreatic duct (APD) commonly drains in the main pancreatic duct (MPD) but can communicate with the intrapancreatic common bile duct, the duct of Santorini, or the duct of Wirsung. Yogi et al. classified AP into six subtypes with type I type demonstrating communication of APD with the duct of Wirsung and type II showing the duodenum encircled by MPD. Types I and II are the most common subtypes with the other 4 subtypes being less frequently encountered and correspond to the communication of the APD with the duct of Santorini or the common bile duct (CBD).