Congenital Abnormalities Pancreas

Several systems are in use for classifying congenital pancreatic duct anomalies. A common scheme is to subdivide anomalies into migration and fusion. The most common is fusion failure between the dorsal and ventral pancreatic ducts (pancreas divisum). Migration variations include pancreatic rests, which are formed by incomplete migration of the prepancreatic anlage.As a result, pancreatic tissue remains in stomach wall, duodenum, and other structures.Likewise, failure of full rotation of the prepancreatic buds results in an annular. In some patients it is difficult to predict whether a detected congenital anomaly is indeed responsible for a particular clinical problem.
Agenesis
Complete agenesis of the pancreas is incompatible with life. Partial agenesis is rare,with either the ventral or dorsal segment failing to develop. This congenital anomaly is associated with polysplenia and intrathoracic anomalies. Agenesis of the dorsal segment results in only the head of the pancreas being present; CT and MR show this segment as an oval mass. Many of these patients also have diabetes mellitus, presumably because of islet cell agenesis, which normally are predominantly located in the body and tail of the pancreas. The uncinate process is either absent or hypoplastic in patients with intestinal nonrotation, presumably secondary to incomplete pancreatic primordial ventral bud rotation. Pancreas Divisum Pancreatography and immunohistochemical staining of pancreatic polypeptide identify two types of dorsal and ventral duct fusion: (1) one-point fusion at the junction of main duct and accessory pancreatic duct, and (2) twopoint fusion not only at the primary duct junction site but also at a second site. Abnormal embryologic fusion (or lack of fusion) of the ventral and dorsal primordia causes pancreas divisum.

radiology images of Schematic configuration of dilated pancreatic ducts. A: Drainage is via the duct of Wirsung. The minor papilla drains only a small portion of the pancreas. B: Pancreas divisum. Most of the pancreas is drained via the duct of Santorini (S). Insertion of the common bile duct marks the major papilla and identifies the duct of Wirsung (W). C: The ducts of Santorini and Wirsung communicate freely but drain through their respective papillae.

Pancreas divisum is the most common congenital anomaly of the pancreas, with autopsy studies showing about a 6% prevalence. Some consider pancreas divisum to be an innocuous congenital variant, while others believe that it is associated with a higher prevalence of pancreatitis. The frequency of pancreas divisum in patients with pancreatitis is significantly higher than in a general population. If found in several family members, is this hereditary pancreatitis in a setting of familial pancreas divisum? Pancreatitis in this patient population often is focal and limited to a dorsal distribution. It is
often technically difficult in these patients to cannulate the dorsal pancreatic duct (duct of Santorini); nevertheless, some endoscopy centers have achieved a high success rate and have become referral centers for this procedure. Pancreas divisum does not appear to predispose to an anomalous pancreaticobiliary duct union.
Pancreas divisum is generally detected by pancreatography.At times CT identifies distinct ventral and dorsal pancreatic ducts. Occasionally CT suggests pancreas divisum by an indistinct mass in the head of the pancreas.
An MRCP detects about half the pancreas divisum anomalies. Secretin administration appears to aid in this detection. The prevalence of both acute relapsing pancreatitis and chronic pancreatitis appears to decrease following minor papilla sphincterotomy and resultant accessory duct decompression. At times stenting of the dorsal pancreatic duct relieves symptoms.

Pancreas divisum. A: Endoscopic retrograde cholangiopancreatography (ERCP) with contrast injection into the main papilla outlines only a short,narrow caliber duct of Wirsung.Parenchymal contrast is evident. B: Computed tomography (CT) identifies a dilated duct (arrow) not conforming to the usual course of the main pancreatic duct.

Annular Pancreas
In neonates an annular pancreas is associated with esophageal atresia, tracheoesophageal fistula, duodenal stenosis or atresia, and malrotation. Rare instances of an annular pancreas and pancreas divisum in the same patient have been reported. Symptoms of an annular pancreas not uncommonly manifest during adulthood, the most common findings being abdominal pain, gastric outlet obstruction, pancreatitis, and a pancreatic tumor.

Radiology images of Duodenal stricture (arrow), believed to be secondary to pancreatitis in an annular pancreas.

In the newborn, conventional radiography of complete obstruction by an annular pancreas shows a “double-bubble” sign with no bowel gas distally. Only in a minority of older individuals does a barium study suggest annular pancreas. CT and MRCP also underdiagnose this condition. At times ERP suggests the diagnosis, although in some patients confirmation is made only at surgery. Computed tomography and MR identify the second part of the duodenum being surrounded by pancreatic tissue; at times a pancreatic duct segment is identified in the annular portion. In some patients this circumferential duodenal narrowing is due mostly to fibrotic tissue. A cyst developing adjacent to the duodenum in a patient with an annular pancreas and repeated attacks of pancreatitis should suggest a (pseudo)cyst.

Radiology images of Annular pancreas. After oral and IV contrast CT shows the pancreas surrounding descending duodenum (arrow).

Ectopic Pancreas
Ectopic (heterotopic) pancreatic tissue is most often found in the gastric antrum and proximal duodenum, although it can be located anywhere in the gastrointestinal tract, including a Meckel’s diverticulum. Inflammation does develop in ectopic pancreatic tissue (called cystic dystrophy of an ectopic pancreas by some authors). If chronic, fibrosis and bowel stenosis ensue. Acute pancreatitis and even a (pseudo)cyst have developed in an ectopic pancreas. Similarly, this tissue is not immune to tumor formation; a carcinoma originated in ectopic pancreatic tissue in the esophagus, and a papillary cystic neoplasm developed in ectopic pancreatic tissue in the omentum.
Aberrant Duct Insertion
During embryonic development a network of duct branches eventually fuses and forms a primary channel. Aberrant fusion leads to a number of duplication anomalies of the pancreatic ducts and results in one or more main duct. This congenital anomaly is often associated with an apparent tumor on CT imaging. The pancreatic duct can communicate with a duodenal duplication or even involve aberrant bile ducts and the patient presents with a periampullary  cystic tumor; CT and ERCP are helpful in defining the underlying anatomy and planning surgery.
Cysts
Congenital cysts of the pancreas are either true cysts or pseudocysts. Both are rare. They range from solitary to multiple. True cysts are lined by epithelium. These cysts in neonates tend to be large and their clinical differential diagnosis often includes renal, choledochal, mesenteric, ovarian, and gastrointestinal origin cysts. An increased prevalence of simple cysts is found in patients with polycystic kidney disease, tuberous sclerosis, and von Hippel- Lindau disease. Incidentally detected multiple pancreatic cysts, especially in a young patient without pancreatic disease, should suggest one
of these entities. Patients with von Hippel- Lindau disease are also prone to developing cystic pancreatic neoplasms. In fact, in an occasional patient pancreatic lesions are the only abdominal manifestation of von Hippel-Lindau
disease.
Computed tomography or MR confirms a cyst’s location and its relationship to pancreatic parenchyma; imaging tends not to differentiate among congenital cysts, a cystic neoplasm, and other cystic lesion. Precontrast CT of a lymphoepithelial cyst revealed a heterogeneous water-density tumor, with septa identified postcontrast; MRI showed a hypointense mass on T1- and a hyperintense mass on T2-weighted imaging, with septa identified on postgadolinium images. Endoscopic US confirmed the presence of septa and also detected fine hyperechoic structures within the cyst. A cystic neoplasm was suspected preoperatively.
Histiocytosis Langerhans cell histiocytosis is the current term for disorders previously known as histiocytosis X. This is a rare disorder, with pancreatic involvement being even rarer.

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