ANNULAR PANCREAS DIVISUM

Annular Pancreas / Pancreas Divisum : The pancreas develops from an anterior and posterior anlage of the foregut early during gestation (28 days). The anterior bud leads to the liver and body and tail of the pancreas. The posterior diverticulum develops into the head of the pancreas. This bud rotates anteriorly and later fuses to achieve the relationship to the rest of the pancreas. Development of the pancreas in embryonic life requires a trophic stimulus from the associated mesenchyme. Under the influence of this mesenchyme the mature organ develops, being mainly composed of ductal, exocrine and endocrine cells. Exocrine and ductal pancreas are derived from the endoderm of the foregut. Recent evidence suggests that the endocrine cells derive also from the endoderm of the foregut as evidenced by the expression of the genes responsible for hormonal production. This challenges the theory that endocrine cells may originate from the neural crest cells (neuroectodermal) of the embryo reinforced by the enunciation of the amine precursor uptake decarboxylase (APUD) theory.

Annular pancreas is the most common congenital malformation of the pancreas in association with duodenal atresia. Embryologically the ring formation (annulus) originates from the ventral pancreas primordium (Lecco's theory). The pancreatic duct of the annular tissue passed from the anterior portion to the lateral and posterior portion finally joining with the main pancreatic duct. Two types of annular pancreas are recognized: 1) Extramural - causing high gastrointestinal obstruction; vomiting is the most common presenting symptom, and 2) Intramural - producing duodenal ulceration. Presentation at birth is affected by the degree of duodenal obstruction and coexistent anomalies. Polyhydramnios usually accompanies complete high intestinal obstruction in annular pancreas. Associated anomalies can range from malrotation, intrinsic duodenal obstruction, Down syndrome and duodenal bands. ERCP is the most important procedure to find the characteristic features and establish the therapeutic strategy in cases of annular pancreas. Experience militates against any direct attack on the offending annulus. Therefore, all children with this abnormality are generally treated with a bypass procedure, preferably a duodeno-duodenostomy. Long-term complications may include cholestatic jaundice, upper gastrointestinal motility disorder, failure to thrive, chronic diarrhea and chronic relapsing pancreatitis due to an incomplete divisum anomaly.

Pancreas divisum (PD), believed the most common congenital anomaly of the pancreas, is an embryologic variation of pancreas development where the dorsal (Santorini) and ventral portions (Wirsung) ducts drain separately. Diagnosis is made with ERCP (short duct of Wirsung that does not communicate with main pancreatic duct of Santorini). Not everybody with this ductal anomaly develops pancreatitis. Likewise with the minor papilla draining the bulk of the pancreas in PD, a small orifice size (< 0.75 mm) plays a role in outflow obstruction and development of pancreatitis. Children with PD and recurrent episodes of pancreatitis will need endoscopic sphincterotomy of the minor and sometimes major papilla. If not feasible technically, surgical sphincteroplasty of both papillae along with cholecystectomy (bile stasis leads to gallstones) is indicated. Intraoperative pancreatogram will help determine if both papilla are stenotic. Once chronic pancreatitis is established, ductal drainage or resection may be necessary.