Annular pancreas

Annular pancreas, pancreas divisum, pancreatic hypoplasia and agenesis, heterotopic pancreas Inherited syndromes affecting the pancreas Cystic fibrosis... 

The main causes for a double bubble are duodenal atresia, annular pancreas, and midgut volvulus. Less frequently it may be secondary to duodenal web, Ladd s band, or preduodenal portal vein (Crowe and Sumner 1978). 

Fig. 1.5a-c. Annular pancreas. Supine (a) and lateral (b) views of the abdomen show complete obstruction at duodenal level identical to that seen in duodenal atresia. The stomach (st) and duodenal bulb (d) are distended and there is no distal air. c Surgical image shows the pancreatic tissue (arrow) encircling the duodenum (d)... 

Partial duodenal obstruction may be produced by duodenal stenosis, duodenal web, Ladd s bands, midgut volvulus, annular pancreas, preduodenal portal vein, and duplication cyst. Plain radiographs show gaseous distension of the stomach and duodenum with a normal or diminished quantity of air in the small bowel. Content studies may be necessary to differentiate between midgut volvulus and partial duodenal obstruction caused by a web or stenosis (Auringer and Sumner 1994). Sonography is helpful to rule out extraluminal causes such as a duplication cyst. 

H-type tradieo-esophageal fistula. The differential diagnosis for the double-bubble should include duodenal stenosis and annular pancreas (Rathaus et al. 1992 Poki et al. 2005). 

Gastric rupture is mainly seen in neonates due to acute distention of the stomach, ischemic necrosis associated with perinatal asphyxia and distal obstruction such as annular pancreas (Ibach and Inouye 1965) or duodenal atresia/stenosis. On the other hand, duodenal rupture in neonates is rare. 

Ibach JR, Inouye WY (1965) Neonatal gastric perforation secondary to annular pancreas. Am J Surg 110 985-987 Itha S, Yachha SK (2006) Endoscopic outcome beyond esophageal variceal eradication in children with extrahepatic portal venous obstruction. J Ped Gastroenterol Nutr 42 196-200... 

In annular pancreas, the duodenum is often compressed at a point distal to the ampulla of Vater, making bilious vomiting a hallmark symptom. Abdominal distention is typically not a feature because of the proximal location of the obstruction. Patients may not pass meconium, or bowel movements may cease abruptly. A more insidious form of chronic partial duodenal obstruction may also occur. 

On CT, an annular pancreas (with or without pancreatitis) may be seen as enlargement of the pancreatic head, surrounding the second portion of the duodenum. Follow up CT may demonstrate calcifications limited to the annulus of the pancreas (Gazelle et al. 1998). 

On ERCP, various ductal configurations may be seen. A classification of six types of annular pancreas according to the site into which the duct of the annulus drains has been reported (Gazelle et al. 1998). 

On MRI, the normal pancreatic tissue has higher signal intensity compared with other tissues on Tl-weighted images with fat saturation. This signal is due to the high concentration of proteins inside the acini. An annular pancreas will be seen on MRI as... 

Fig. 4.15. a Classic UGI image of annular pancreas, b MRCP image of an annular pancreas causing relative obstruction of the descending duodenum... 

Annular pancreas with complete or incomplete duodenal obstruction is another cause of duodenal obstruction. Its cause is persistence of the left lobe of the ventral pancreatic bud around the sixth week of gestation that then raps around the duodenum causing a ring-like eccentric narrowing (Fig. 5.7b). The clinical and radiological findings are the same... 

Fig. 5.7. a Duodenal stenosis caused by a duodenal web with a windsock appearance, b Eccentric narrowing of the descending duodenum at the level of the sphincter of Oddi annular pancreas... 

Fig. 2.37a-c. Annular Pancreas. Double Contrast barium study (a) demonstrates semicircumferential narrowing of the duodenum due to an annular pancreas. Note the biliary stent. ERCP (b) shows the pancreatic ductal system encircling the duodenum. MRI (c) shows the pancreatic head, folded around the duodenal lumen... 

A ring-like deformity of the mid-part of the descending duodenum is sometimes seen in cases of annular pancreas, i.e. incomplete rotation of the ventral component, leaving either a strand of pancreatic cells or just a fibrotic ring behind. This congenital defect is in most instances an incidental finding. 

Fig. 4.15. Annular pancreas. A typical stricture in the second part of the duodenum in a patient with an annular pancreas. Note the uninterrupted mucosal pattern explaining why endoscopy is often negative...

Jadvar H, Mindelzun RE (1999) Annular pancreas in adults imaging features in seven patients. Abdominal Imaging 24 174-177... 

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