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Annular pancreas

Annular pancreas
Literature review current through: Jan 2024.
This topic last updated: Sep 26, 2022.

INTRODUCTION — Annular pancreas is a rare congenital abnormality characterized by a ring of pancreatic tissue surrounding the descending portion of the duodenum. It is thought to originate from incomplete rotation of the ventral pancreatic bud. This topic will review the pathogenesis, clinical manifestations, diagnosis, and management of annular pancreas. Other causes of duodenal obstruction and congenital abnormalities of the pancreas, including pancreas divisum, are discussed in detail, separately. (See "Intestinal malrotation in children" and "Intestinal atresia" and "Pancreas divisum: Clinical manifestations and diagnosis".)

EPIDEMIOLOGY — The exact prevalence of annular pancreas is unclear as many individuals with annular pancreas are asymptomatic. In autopsy series in which duodenal dissection has been performed, the prevalence of annular pancreas ranges from 5 to 15 per 100,000 adults [1-3]. Annular pancreas has been associated with maternal polyhydramnios and congenital abnormalities such as Down syndrome, esophageal and duodenal atresia, imperforate anus, and Meckel's diverticulum [4-6]. (See "Down syndrome: Clinical features and diagnosis" and "Intestinal atresia" and "Meckel's diverticulum".)  

EMBRYOLOGY AND PATHOGENESIS — The pancreas develops from one dorsal and two ventral buds that first appear as evaginations of the primitive foregut at around the fifth week of gestation. Due to selective expansion of the duodenum, by approximately the seventh week, the ventral bud rotates with the gut, passing behind the duodenum from the right to left and eventually fusing with the dorsal bud. The ventral bud forms the inferior part of the head of the pancreas and the uncinate process, whereas the dorsal bud becomes the tail and the body. Fusion of the ductular network of the two buds gives rise to the main pancreatic duct. The accessory pancreatic duct, which often persists, is derived from the dorsal pancreatic duct proximal to the site of fusion (figure 1) [7-9].

Annular pancreas results from failure of the ventral bud to rotate with the duodenum, causing envelopment of duodenum. Three major theories have been proposed to explain the development of annular pancreas:

Adherence of the ventral bud to the duodenal wall prior to rotation, resulting in its persistence and encirclement of the duodenum (Lecco's theory) [10].

Persistence and enlargement of the left ventral bud (Baldwin's theory) [11].

Hypertrophy and fusion of the ventral and dorsal buds before rotation of the gut, resulting in complete encirclement of the duodenum [12].

In individuals with annular pancreas, the annulus is usually comprised of a band of pancreatic tissue that encircles the second portion of the duodenum (figure 1). On occasion, this encirclement is incomplete, leaving the anterior portion of the duodenum unconstricted. The pancreatic band is usually interspersed with the duodenal muscularis, although it can also be free from the duodenum. The ventral duct generally courses posteriorly to join the main duct on the left. However, the ventral duct can also course anteriorly from right to left, or there can be multiple small ducts, each with separate openings into the duodenum [12,13]. Approximately one-third to one-half of patients with annular pancreas also have pancreas divisum, a congenital anomaly characterized by failure of fusion of the ventral and dorsal duct system. (See 'Classification' below and "Pancreas divisum: Clinical manifestations and diagnosis", section on 'Embryology'.)

The pathogenesis of pancreatitis in individuals with annular pancreas remains unclear. It is hypothesized that pancreatitis may result from fibrosis leading to partial obstruction of the pancreatic duct in the head of the pancreas. Pancreatic fibrosis in acute pancreatitis is usually limited to the annulus and adjoining pancreatic head, whereas the body and tail are generally spared [14,15]. Peptic ulcers with annular pancreas are often postbulbar. Obstructive gastrointestinal symptoms result from duodenal obstruction due to scarring from repeated pancreatic inflammation or from peptic ulcer disease. Obstruction of the intrapancreatic portion of the common bile duct due to edema and fibrosis of the pancreatic head can result in obstructive jaundice [16-18].

CLASSIFICATION

Based on the anatomic distribution of the pancreatic parenchyma around the duodenum, annular pancreas is classified into the following [19]:

Complete annular pancreas – The pancreatic parenchyma or annular duct completely surround the second portion of the duodenum.

Incomplete annular pancreas – The annulus does not surround the duodenum completely but extends in the posterolateral or anterolateral direction to the second part of the duodenum or anterior and posterior to the duodenum.

Based upon the drainage site of the annular duct, annular pancreas is classified into six subtypes. Of these, type I and II are the most common variants [20].

Type I – The annular duct flows directly into the main pancreatic duct

Type II – The duct of Wirsung encircles the duodenum but drains at the major papilla

Type III – The annular duct drains into the common bile duct from the dorsal side

Type IV – The annular duct drains into the common bile duct without the duct of Wirsung

Type V – The annular duct drains into the duct of Santorini from the ventral site

Type VI – The annular duct drains into the duct of Santorini with malfusion

CLINICAL MANIFESTATIONS — Approximately two-thirds of patients with annular pancreas are asymptomatic. The age of onset of symptoms depends upon the severity of duodenal obstruction [14]. More than two-thirds of children present during the neonatal period with feeding intolerance, vomiting, and abdominal distension [21]. As annular pancreas often lies proximal to the major papilla, emesis is usually nonbilious [22].

Most adults present with symptoms between the ages of 20 and 50 years [23]. Adults usually present with chronic abdominal pain, nausea, postprandial fullness, and vomiting. Other symptoms include upper gastrointestinal bleeding from peptic ulceration, acute or chronic pancreatitis, and, rarely, jaundice due to biliary obstruction [23-26]. (See "Unusual causes of peptic ulcer disease", section on 'Obstruction'.)

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of annular pancreas varies based on the age at diagnosis and the clinical presentation. Annular pancreas can be differentiated from these by abdominal imaging. (See 'Diagnosis' below.)

In neonates, the differential diagnosis includes pyloric stenosis, intestinal atresia, and intestinal malrotation. (See "Approach to the infant or child with nausea and vomiting", section on 'Disorders primarily seen in neonates and young infants'.)

In adults presenting with abdominal pain, nausea, and postprandial fullness, the differential diagnosis of annular pancreas includes other causes of dyspepsia including peptic ulcer disease, gastroesophageal reflux disease, and biliary pain. Other causes of obstructive jaundice in adults include choledocholithiasis, biliary obstruction from other malignant tumors or adenomas, and intrahepatic cholestasis [18,20]. (See "Approach to the adult with dyspepsia", section on 'Etiology' and "Diagnostic approach to the adult with jaundice or asymptomatic hyperbilirubinemia", section on 'Evaluation for intrahepatic cholestasis'.)

DIAGNOSIS — Annular pancreas should be suspected in infants and children with feeding intolerance, abdominal distension, and vomiting. In adults, annular pancreas is usually diagnosed incidentally during the course of evaluation of abdominal pain. The diagnosis of annular pancreas is established by the presence of pancreatic tissue surrounding the descending portion of the duodenum on abdominal imaging. (See 'Abdominal imaging' below.)

The evaluation of nausea and vomiting in childhood and abdominal pain in adults is discussed in detail elsewhere. (See "Approach to the infant or child with nausea and vomiting", section on 'Evaluation' and "Evaluation of the adult with abdominal pain".)

Abdominal imaging — In infants, abdominal radiographic findings are suggestive of annular pancreas, but are not diagnostic. However, no further testing is usually required because all patients in this age group with complete or partial duodenal obstruction require surgical correction. A definitive diagnosis is therefore made at the time of laparotomy [12]. In older children and adults, the diagnosis is established with an upper gastrointestinal (GI) series or an abdominal computed tomography (CT) scan (image 1), respectively. We perform a magnetic resonance cholangiopancreatography (MRCP) when the results from upper GI series or abdominal CT findings are equivocal and in patients whose symptoms are unexplained. We reserve endoscopic retrograde cholangiopancreatography (ERCP) for patients in whom a periampullary malignancy is suspected on MRCP or abdominal CT scan. Although endoscopic ultrasound has been used in patients with annular pancreas, its role in the work-up of annular pancreas has not been established [27,28].

Abdominal radiographs — In symptomatic neonates, a plain abdominal radiograph will show the classic "double bubble" sign with air in the stomach and duodenum. However, the double bubble sign is not specific for annular pancreas since it can also be seen in other conditions including duodenal atresia and intestinal malrotation [29-32]. (See "Intestinal atresia", section on 'Imaging' and "Intestinal malrotation in children", section on 'Diagnosis'.)

Upper gastrointestinal series — Findings on upper GI series that are suggestive of annular pancreas include duodenal narrowing with an eccentric or concentric narrowing of the second portion of the duodenum and symmetrical dilatation of the proximal duodenum. Reverse peristalsis of the duodenal segment proximal to the annulus and dilation of the duodenum distal to the annulus may also be seen [23,26].

Abdominal CT scan — Abdominal CT scan findings consistent with annular pancreas include descending duodenal narrowing and ring of pancreatic tissue encircling the duodenum. The ring may completely encircle the pancreas or, in patients with incomplete annular pancreas, pancreatic tissue may extend posterolateral or anterolateral direction to the second part of the duodenum or anterior and posterior to the duodenum in a crocodile jaw configuration.

Cholangiopancreatogram — Secretin-enhanced MRCP and ERCP allow for the exact delineation of the anatomic structure of the accessory pancreatic duct and the annular duct encircling the descending duodenum [23,33-36].

ADDITIONAL EVALUATION — Specific studies may be required to evaluate infants and children for associated congenital anomalies, especially in the presence of Down syndrome (eg, cardiac assessment with an echocardiogram, renal ultrasound) [37]. In some cases, testing may be required prior to surgery. (See "Down syndrome: Clinical features and diagnosis" and "Down syndrome: Management", section on 'Cardiac disease'.)

MANAGEMENT — Most patients with annular pancreas are asymptomatic, and thus the presence of annular pancreas does not necessarily indicate that symptoms can be attributed to it. Although endoscopic therapy has been described, surgery remains the procedure of choice in patients in whom symptoms can be attributed to annular pancreas [38]. The goal of surgery is to relieve duodenal or gastric outlet obstruction by bypassing the annulus [12,26]. Resection of the annulus should be avoided since it is associated with pancreatitis, pancreatic fistula formation, and incomplete relief of obstruction [5,36].

In neonates, relief of obstruction is accomplished with a duodenoduodenostomy. In adults, a duodenojejunostomy or gastrojejunostomy is recommended as the duodenum is less mobile [39,40]. In patients with annular pancreas associated with obstructive jaundice, biliary bypass with choledochoenterostomy or placement of a biliary stent may be necessary to relieve the obstruction [16,17]. Pancreaticoduodenectomy has been recommended when annular pancreas is associated with obstructive pancreatic duct stones in the setting of chronic pancreatitis or a periampullary lesion that is suspicious for a malignancy [18,41]. (See "Pylorus-preserving pancreaticoduodenectomy" and "Chronic pancreatitis: Clinical manifestations and diagnosis in adults".)

PROGNOSIS — The prognosis of patients with annular pancreas depends largely upon the age of onset of symptoms [12]. In infants and children, the prognosis largely depends on the associated congenital abnormalities [22,42]. Most adults with annular pancreas have a good prognosis and do not require treatment. In adults, morbidity and mortality are mainly related to surgical complications of bypass procedures [6,12]. (See "Pylorus-preserving pancreaticoduodenectomy", section on 'Complications'.)

SUMMARY AND RECOMMENDATIONS

Annular pancreas is a rare congenital abnormality characterized by a ring of pancreatic tissue surrounding the descending portion of the duodenum. (See 'Introduction' above.)

In autopsy series, the prevalence of annular pancreas ranges from 5 to 15 per 100,000 adults. Annular pancreas has been associated with maternal polyhydramnios and congenital abnormalities such as Down syndrome, esophageal and duodenal atresia, imperforate anus, and Meckel's diverticulum. (See 'Epidemiology' above.)

Annular pancreas results from failure of the ventral bud to rotate with the duodenum, causing envelopment of duodenum. The pancreatic parenchyma or annular duct may completely surround the second portion of the duodenum or extend in the posterolateral or anterolateral direction to the second part of the duodenum or anterior and posterior to the duodenum. (See 'Classification' above.)

Pancreatitis may result from partial obstruction of the pancreatic duct, mainly occurring within the head of the pancreas. Peptic ulcers with annular pancreas are often postbulbar. Obstructive gastrointestinal symptoms result from duodenal obstruction due to scarring from repeated pancreatic inflammation or from peptic ulcer disease. Obstruction of the intrapancreatic portion of the common bile duct due to edema and fibrosis of the pancreatic head can result in obstructive jaundice. (See 'Embryology and pathogenesis' above.)

Approximately two-thirds of patients with annular pancreas are asymptomatic. The age of onset of symptoms depends upon the severity of duodenal obstruction. More than two-thirds of children present during the neonatal period, typically with features of gastric outlet obstruction including feeding intolerance, vomiting, and abdominal distension. Adults may present with abdominal pain, duodenal obstruction, peptic ulcers, acute or chronic pancreatitis, or obstructive jaundice. (See 'Clinical manifestations' above.)

Annular pancreas should be suspected in infants and children with feeding intolerance, abdominal distension, and vomiting. In adults, annular pancreas is usually diagnosed incidentally during the course of evaluation of the patient's symptoms of abdominal pain. The diagnosis of annular pancreas is established by the presence of pancreatic tissue surrounding the descending portion of the duodenum on abdominal imaging. (See 'Diagnosis' above.)

In infants, abdominal radiographic findings are suggestive of annular pancreas but not diagnostic. However, no further testing is usually required because all patients in this age group with complete or partial duodenal obstruction require surgical correction. A definitive diagnosis is therefore made at the time of laparotomy. In older children and adults, the diagnosis is established with an upper gastrointestinal (GI) series or an abdominal computed tomography (CT) scan (image 1), respectively. We perform a magnetic resonance cholangiopancreatography (MRCP) when the results from upper GI series or CT are equivocal. We reserve endoscopic retrograde cholangiopancreatography (ERCP) for patients in whom a periampullary malignancy is suspected on MRCP or abdominal CT scan. (See 'Abdominal imaging' above.)

Most patients with annular pancreas are asymptomatic and thus the presence of annular pancreas does not necessarily indicate that symptoms can be attributed to it. In both children and adults with symptomatic annular pancreas, we suggest bypass surgery of the annulus (Grade 2C). Resection of the annulus should be avoided since it is associated with pancreatitis, pancreatic fistula formation, and incomplete relief of obstruction. (See 'Management' above.)

  1. Ravitch MM. The pancreas in infants and children. Surg Clin North Am 1975; 55:377.
  2. THEODORIDES T. [ANNULAR PANCREAS]. J Chir (Paris) 1964; 87:445.
  3. RAVITCH MM, WOODS AC Jr. Annular pancreas. Ann Surg 1950; 132:1116.
  4. HAYS DM, GREANEY EM Jr, HILL JT. Annular pancreas as a cause of acute neonatal duodenal obstruction. Ann Surg 1961; 153:103.
  5. Sencan A, Mir E, Günsar C, Akcora B. Symptomatic annular pancreas in newborns. Med Sci Monit 2002; 8:CR434.
  6. Zyromski NJ, Sandoval JA, Pitt HA, et al. Annular pancreas: dramatic differences between children and adults. J Am Coll Surg 2008; 206:1019.
  7. Moodley S, Hegarty M, Thomson SR. Annular pancreas. S Afr Med J 2004; 94:28.
  8. Lee PC, Lebnethal E. Prenatal and postnatal development of the human exocrine pancreas. In: Pancreas: Pathology, Pathobiology and Disease, 2nd ed, Go VL, Dimagno EP, Gardner JD, et al (Eds), Raven Press, New York 1993. p.57.
  9. Kozu T, Suda K, Toki F. Pancreatic development and anatomical variation. Gastrointest Endosc Clin N Am 1995; 5:1.
  10. Laughlin EH, Keown ME, Jackson JE. Heterotopic pancreas obstructing the ampulla of Vater. Arch Surg 1983; 118:979.
  11. Baldwin W. A specimen of annular pancreas. Anat Rec 1910; 4:299.
  12. Hill ID, Lebenthal E. Congenital abnormalities of the exocrine pancreas. In: Pancreas: Pathology, Pathobiology and Disease, 2nd ed, Go VL, Dimagno EP, Gardner JD, et al (Eds), Raven Press, New York 1993. p.1029.
  13. Lin SZ. Annular pancreas. Etiology, classification and diagnostic imaging. Chin Med J (Engl) 1989; 102:368.
  14. Cunha JE, de Lima MS, Jukemura J, et al. Unusual clinical presentation of annular pancreas in the adult. Pancreatology 2005; 5:81.
  15. Gilinsky NH, Lewis JW, Flueck JA, Fried AM. Annular pancreas associated with diffuse chronic pancreatitis. Am J Gastroenterol 1987; 82:681.
  16. Baggott BB, Long WB. Annular pancreas as a cause of extrahepatic biliary obstruction. Am J Gastroenterol 1991; 86:224.
  17. Green JD, Fieber SS, Buniak B. Annular pancreas with dilated biliary and pancreatic ducts. Am J Gastroenterol 1993; 88:467.
  18. Shan YS, Sy ED, Lin PW. Annular pancreas with obstructive jaundice: beware of underlying neoplasm. Pancreas 2002; 25:314.
  19. Sandrasegaran K, Patel A, Fogel EL, et al. Annular pancreas in adults. AJR Am J Roentgenol 2009; 193:455.
  20. Yogi Y, Shibue T, Hashimoto S. Annular pancreas detected in adults, diagnosed by endoscopic retrograde cholangiopancreatography: report of four cases. Gastroenterol Jpn 1987; 22:92.
  21. Kiernan PD, ReMine SG, Kiernan PC, ReMine WH. Annular pancreas: May Clinic experience from 1957 to 1976 with review of the literature. Arch Surg 1980; 115:46.
  22. Jimenez JC, Emil S, Podnos Y, Nguyen N. Annular pancreas in children: a recent decade's experience. J Pediatr Surg 2004; 39:1654.
  23. Urayama S, Kozarek R, Ball T, et al. Presentation and treatment of annular pancreas in an adult population. Am J Gastroenterol 1995; 90:995.
  24. Chen YC, Yeh CN, Tseng JH. Symptomatic adult annular pancreas. J Clin Gastroenterol 2003; 36:446.
  25. England RE, Newcomer MK, Leung JW, Cotton PB. Case report: annular pancreas divisum--a report of two cases and review of the literature. Br J Radiol 1995; 68:324.
  26. Maker V, Gerzenshtein J, Lerner T. Annular pancreas in the adult: two case reports and review of more than a century of literature. Am Surg 2003; 69:404.
  27. Gress F, Yiengpruksawan A, Sherman S, et al. Diagnosis of annular pancreas by endoscopic ultrasound. Gastrointest Endosc 1996; 44:485.
  28. Papachristou GI, Topazian MD, Gleeson FC, Levy MJ. EUS features of annular pancreas (with video). Gastrointest Endosc 2007; 65:340.
  29. Poki HO, Holland AJ, Pitkin J. Double bubble, double trouble. Pediatr Surg Int 2005; 21:428.
  30. Imamoglu M, Cay A, Sarihan H, Sen Y. Rare clinical presentation mode of intestinal malrotation after neonatal period: Malabsorption-like symptoms due to chronic midgut volvulus. Pediatr Int 2004; 46:167.
  31. Yoshizato T, Satoh S, Taguchi T, et al. Intermittent 'double bubble' sign in a case of congenital pyloric atresia. Fetal Diagn Ther 2002; 17:334.
  32. Malone FD, Crombleholme TM, Nores JA, et al. Pitfalls of the 'double bubble' sign: a case of congenital duodenal duplication. Fetal Diagn Ther 1997; 12:298.
  33. Itoh Y, Hada T, Terano A, et al. Pancreatitis in the annulus of annular pancreas demonstrated by the combined use of computed tomography and endoscopic retrograde cholangiopancreatography. Am J Gastroenterol 1989; 84:961.
  34. Choi JY, Kim MJ, Kim JH, et al. Annular pancreas: emphasis on magnetic resonance cholangiopancreatography findings. J Comput Assist Tomogr 2004; 28:528.
  35. Chevallier P, Souci J, Buckley MJ, et al. Annular pancreas: MR imaging including MR cholangiopancreatography (MRCP). Pancreas 1999; 18:216.
  36. Hidaka T, Hirohashi S, Uchida H, et al. Annular pancreas diagnosed by single-shot MR cholangiopancreatography. Magn Reson Imaging 1998; 16:441.
  37. Kimble RM, Harding J, Kolbe A. Additional congenital anomalies in babies with gut atresia or stenosis: when to investigate, and which investigation. Pediatr Surg Int 1997; 12:565.
  38. Gromski MA, Lehman GA, Zyromski NJ, et al. Annular pancreas: endoscopic and pancreatographic findings from a tertiary referral ERCP center. Gastrointest Endosc 2019; 89:322.
  39. De Ugarte DA, Dutson EP, Hiyama DT. Annular pancreas in the adult: management with laparoscopic gastrojejunostomy. Am Surg 2006; 72:71.
  40. Thomford NR, Knight PR, Pace WG, Madura JA. Annular pancreas in the adult: selection of operation. Ann Surg 1972; 176:159.
  41. Benger JR, Thompson MH. Annular pancreas and obstructive jaundice. Am J Gastroenterol 1997; 92:713.
  42. Mustafawi AR, Hassan ME. Congenital duodenal obstruction in children: a decade's experience. Eur J Pediatr Surg 2008; 18:93.
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