Annular Pancreas

Annular pancreas (AP) is a rare congenital anomaly consisting of a ring of pancreatic tissue partially or completely encircling the second part of the duodenum (1). Most cases are diagnosed in the neonatal period with symptoms of gastric outlet obstruction. We report an unusual case of AP presenting with acute upper gastrointestinal (GI) bleeding in a child. A 12-year-old boy of Malay origin presented with a 1-day history of sudden onset of hematemesis and passing malaenic stools. Before presentation, he had a 1-year history of intermittent postprandial abdominal bloatedness with mild epigastric pain and rare episode of nonbilious vomiting. He tolerated his meals well and showed normal growth along the 75th percentile for both height and weight. Physical examination revealed a pale boy with clinical evidence of hypovolemic shock. He had epigastric tenderness and per rectal examination revealed malaenic stools. The abdomen was not distended and the rest of the physical examination was normal. He required fluid resuscitation to stabilize his vital parameters and was commenced on intravenous omeprazole infusion. Empirical triple therapy for Helicobacter pylori infection comprising amoxicillin, metronidazole, and omeprazole was also started. Initial blood tests showed hemoglobin of 12.6 g/dL (normal 9–14), which dropped to 10.4 g/dL the following day, subsequent to that hemoglobin was stable. Coagulation profile, liver function test, C-reactive protein, and amylase were normal. His GI bleeding resolved within 48 hours with conservative management. Upper GI endoscopy performed on day 3 showed severe gastric erythema at the gastric antrum with a 3-mm irregularly shaped healing ulcer. The stomach antrum and the first part of duodenum (D1) were markedly dilated with stenosis at the junction of second and third part of duodenum (D2-D3). Duodenal mucosa was slightly erythematous with no ulceration (Fig. 1). Histology of the mucosa showed chronic gastritis and mild reflux esophagitis with no evidence of H pylori. The initial clinical impression was duodenal stenosis caused by extrinsic compression or a duodenal web.FIGURE 1: Upper gastrointestinal endoscopy showing slightly erythematous duodenum, dilated D1, and stenosis at the D2/D3 junction.Magnetic resonance imaging of the abdomen was suggestive of AP; it showed an extension of the pancreatic head traversing from the left to the right side, with a component encircling the second (D2) segment of the duodenum. The first and second parts of the duodenum were dilated to the level of a short narrowing in distal D2 measuring 7 mm in width and extending for 15 mm (Fig. 2).FIGURE 2: Axial magnetic resonance imaging (Skyra) postcontrast image showing extension of pancreatic head (solid arrowhead) traversing anterior aspect of the dilated D2 segment of the duodenum (asterisk).The child underwent an elective Roux-en-Y duodenoduodenostomy to bypass the annulus. Intraoperative findings showed a large, dilated, and floppy duodenum (D1 and part of D2) surrounded by AP traversing the anterior aspect of the duodenum (Fig. 3). The duodenum below the narrowing was of normal calibre. The stomach and pylorus were normal. The child made an uneventful recovery from the operation, and on 3-month follow-up all of his symptoms had resolved.FIGURE 3: Intraoperative laparoscopy findings of annular pancreas (solid arrow head) traversing anterior aspect of the duodenum, which was abnormally dilated (asterix).DISCUSSION AP, first described by Tiedemann in 1818, is a rare congenital anomaly commonly presenting in infancy. Normally, the pancreas develops from 1 dorsal and 2 ventral buds that first appear as evaginations of the primitive foregut at around the fifth week of gestation. Because of selective expansion of the duodenum by the seventh week, the ventral bud rotates with the gut, passing behind the duodenum from right to left and eventually fusing with the dorsal bud. AP arises from the failure of the ventral bud to rotate with the duodenum, resulting in encircling of the duodenum. The encirclement may be incomplete, leaving the anterior portion of the duodenum unconstricted. The annulus usually comprises pancreatic tissue that encircles the second part of the duodenum (2) (Fig. 4).FIGURE 4: A–C, Normal embryonic development of pancreas. D, Embryonic development of annular pancreas. Adapted from (2).AP presents predominantly in infancy with features of gastric outlet obstruction, including feeding intolerance, vomiting, and abdominal distension (3). Up to 50% of cases are associated with congenital anomalies, including Down syndrome, tracheoesophageal fistula, esophageal atresia, imperforate anus, and Hirschsprung disease. In a retrospective review of cases with AP in 2 pediatric surgical centers (4), all 16 patients presented with nonbilious vomiting: 75% within the first week of life, whereas the remainder presented within the first year. Lin et al (5) also described vomiting as the most common presenting symptom in a series of 15 pediatric patients with median age at operation of 4 days. AP is rare in adults, usually presenting in the fourth or fifth decade. In contrast to children, predominant features are chronic low-grade obstructive symptoms and pancreatitis (6). To our knowledge, this is the first reported case of a child with AP presenting with sudden-onset upper GI bleeding. The gastritis and peptic ulcer in the antrum seen during upper GI endoscopy was the most likely cause for the GI bleeding. The endoscopic findings of duodenal obstruction were unexpected but are in keeping with AP. Duodenal obstruction may have caused the dilated duodenum and stomach to become ptotic over time and resulted in angulation at the portion of duodenum fixed by the AP (6). Stasis of food within the antrum occurs, which in turn accentuates the hormonal phase of gastric secretion. The annulus may also prevent regurgitation of the neutralizing alkaline secretions of the duodenum. As a result, peptic ulcers may have developed in the duodenum or stomach, which can lead to acute upper GI bleeding. Diagnosis of AP is usually established by radiological imaging. In older children or adults, upper GI series or computed tomography/magnetic resonance imaging is the study of choice, showing extrinsic compression of the duodenum. Endoscopic retrograde cholangiopancreatography allows for the exact delineation of the anatomic structure of the accessory pancreatic duct and the C-loop duct encircling the duodenum (7). Magnetic resonance cholangiopancreatography is a noninvasive alternative for visualizing the pancreatic duct encircling the duodenum (8); however, the definitive diagnosis remains at surgery. The treatment of choice is surgical bypass of the annulus, which can be achieved via a duodenoduodenostomy or duodenojejunostomy (3). In summary, AP commonly presents with duodenal obstruction and children undergo surgical bypass early in life, thus precluding the complications of chronic duodenal obstruction, including development of bleeding peptic ulcerations. Our case highlights a rare and potentially life-threatening presentation of AP, especially in an older child. Endoscopists should consider this differential diagnosis when faced with an unusual obstructive anatomy in the duodenum.