4v14 0010 Mp 174 Sunday Jan 24 02:47 PM SV-Ab Image (v. 23, #6) 0010 (1597) Abdom Imaging 24:174-177 (1999) Abdominal I maging  Springer-Verlag New York Inc. 1999 Annular pancreas in adults: imaging features in seven patients H. Jadvar, R. E. Mindelzun Department of Radiology, Stanford University School of Medicine, 300 Pasteur Drive, Room H-1307, Stanford, CA 94305-5105, USA Received: 22 October 1997/Revision accepted: 17 December 1997 Abstract Background: Annular pancreas is a rare congenital ab- normality that may be associated with variable degrees of duodenal obstruction. This diagnosis is often over- looked in adult patients who present with symptoms suggestive of duodenal obstruction. Imaging evaluation aids in establishing the diagnosis. We evaluated the im- aging findings in seven adult patients with known an- nular pancreas. Methods: Seven adult patients with abdominal symptoms had evaluation with one or more of the following imaging studies: upper gastrointestinal (UGI) series, computed to- mography (CT), and endoscopic retrograde cholangio- pancreatography (ERCP). All patients underwent subse- quent laparotomy as a part of routine care. Surgical and imaging findings were correlated in each patient. Results: UGI series is suitable for demonstrating different degrees of duodenal narrowing at the level of pancreatic annulus. Contrast-enhanced abdominal CT is useful in visualizing directly the complete or partial annular pan- creatic tissue. ERCP is particularly useful in visualizing the annulus duct coursing around the duodenum. Conclusions: Imaging plays a pivotal role in the diag- nosis of annular pancreas in adult patients avoiding sur- gery for confirmation with its associated cost and risks. Key words: Annular — Pancreas — Duodenum — Obstruction. An annular pancreas is a rare congenital anomaly that normally presents in childhood as the second most com- mon pancreatic aberration, after pancreas divisum [1]. Although the exact etiology is unknown, several theo- ries have been proposed. Tieken proposed that the an- Correspondence to: R. E. Mindelzun nulus represents hypertrophy of the pancreatic head tis- sue [2]. Lecco suggested that adherence of the tip of the right ventral pancreatic tissue to the duodenal wall re- sults in a ring of tissue around the duodenum at the time of dorsal rotation [2]. Baldwin postulated that the an- nulus results from the abnormal migration and rotation of the ventral anlagen of the pancreatic head, leaving a ring of normal pancreatic tissue around the duodenum [2]. The more accepted theories are those by Lecco [1] or Baldwin [2]. It involves the descending duodenum in 85% of cases and the first and third portions in the re- maining 15% [1, 3]. The ring may be complete, or in some individuals only a smaller portion of pancreas (partial ring) will incompletely encircle the duodenum. Histologically, approximately 2–5 cm of normal pan- creatic tissue is intermixed with the smooth muscle of the duodenal muscularis extending close to the mucosa [1]. Several congenital anomalies are associated with an- nular pancreas in up to 75% of patients. These congen- ital anomalies include trisomy-21 (Down syndrome), tracheoesophageal fistula, esophageal atresia, imperfo- rate anus, and Hirschsprung disease [1]. Duodenal ob- struction may also occur in association with annular pancreas. However, the significance of annular pancreas as the cause of duodenal obstruction is unclear because there are often associated abnormalities such as duo- denal atresia, web, or stenosis. The degree of obstruc- tion prescribes the age when the clinical manifestations are observed. The greater the obstruction, the younger will be the patient at the time of clinical presentation. Discovery at autopsy is rare [1]. In adults, symptoms are directly related to the de- gree of duodenal obstruction. In some cases, the ob- struction is not significant until inflammation of the an- nulus narrows the duodenum or the diagnosis is made incidentally when the patient is evaluated for symptoms of pancreatitis or peptic ulcer disease [1]. In adults, the