An abnormal ring of pancreas that encircles the duodenum and often causes intestinal obstruction. Annular pancreas: An abnormal ring of pancreas that encircles the duodenum and often causes intestinal obstruction. Nausea and vomiting are the usual symptoms and reflect the intestinal obstruction. Complete obstruction is usually evident in the newborn period. Partial obstruction may not present until later in childhood or adulthood. Diagnostic tests include upper GI series, abdominal CT scan, and endoscopy. The treatment is surgical. Complications include peptic ulcer disease and perforation of the intestine. "Annular" is the adjective for "annulus" (a little ring).