Annular pancreas
Annular pancreas is a rare congenital anomaly in which a ring of pancreatic tissue encircles the duodenum. It may cause duodenal obstruction in a newborn, or remain silent for decades and present for the first time in adult life. Many cases are found incidentally and need nothing done.
How it forms
During normal development the pancreas arises from two buds off the embryonic foregut. The ventral bud, which shares its origin with the biliary system, normally rotates clockwise behind the duodenum to lie alongside the dorsal bud, and the two fuse to form a single gland positioned entirely behind and to the left of the duodenum.
In annular pancreas this rotation goes wrong. The favoured explanation is that part of the ventral bud becomes fixed to the duodenal wall before rotation is complete, so that as the duodenum rotates, the tethered pancreatic tissue is dragged around it. The result is a collar of normal pancreatic tissue, complete or partial, encircling the second part of the duodenum. The tissue itself is histologically normal pancreas, containing its own duct which usually drains into the main pancreatic duct.
Two consequences follow. The ring may constrict the duodenum, producing obstruction — complete in the newborn, or partial and slowly progressive in the adult as the tissue undergoes fibrosis or inflammation over the years. And the pancreatic tissue within the ring is subject to the same diseases as the rest of the gland, so pancreatitis within an annulus can precipitate obstruction that was not previously apparent.
Annular pancreas is associated with other congenital abnormalities, particularly in neonates — Down syndrome, duodenal atresia or stenosis, malrotation, cardiac defects and oesophageal atresia among them — which is why a newborn with annular pancreas is assessed for associated anomalies rather than for the pancreas alone.
Symptoms
In infancy
Presents with features of duodenal obstruction: bilious vomiting in the first days of life, feeding intolerance, upper abdominal distension. Polyhydramnios may have been noted during pregnancy, and antenatal ultrasound may have shown the "double bubble" appearance of a distended stomach and proximal duodenum.
In adults
Often silent, and increasingly discovered incidentally on CT performed for another reason. When symptomatic, features are those of partial duodenal obstruction developing gradually:
- postprandial fullness, nausea and vomiting
- upper abdominal pain
- early satiety and weight loss
- episodes of pancreatitis
- peptic ulceration, which is described in association with the condition
- obstructive jaundice, uncommonly, where the biliary anatomy is also involved
How the diagnosis is made
CT with contrast is usually diagnostic in adults, showing pancreatic tissue encircling the duodenum and duodenal narrowing at that level. MRI with MRCP demonstrates the ductal anatomy, including the annular duct, which is valuable if surgery is contemplated.
Upper gastrointestinal contrast studies show narrowing of the second part of the duodenum with proximal dilatation. Endoscopy shows extrinsic compression and excludes intrinsic causes of obstruction — importantly, a tumour, which is the main alternative diagnosis in an adult presenting with duodenal narrowing. Endoscopic ultrasound assists where the distinction is unclear.
In neonates the diagnosis is frequently made at operation for duodenal obstruction, the annulus being found as the cause.
Treatment
No treatment
An incidental annular pancreas causing no symptoms requires no intervention. This is worth stating plainly, as the finding sounds alarming on a radiology report.
Surgery
Where obstruction is symptomatic, the operation bypasses the obstruction rather than removing the ring. This is the central surgical principle: dividing or resecting the annulus risks injury to the ducts within it and to the duodenum, with a substantial risk of pancreatic fistula, and it does not reliably relieve the obstruction because the duodenum is frequently intrinsically narrowed as well.
Standard options are:
- Duodenoduodenostomy — joining the duodenum above the obstruction to the duodenum below it. The preferred procedure in infants, commonly performed as a diamond-shaped anastomosis, and increasingly laparoscopically.
- Duodenojejunostomy — joining the dilated proximal duodenum to a loop of jejunum. Often used in adults.
- Gastrojejunostomy — bypassing at the level of the stomach, used in selected adult cases.
Resection — pancreaticoduodenectomy — is reserved for situations where a tumour cannot be excluded, or where established chronic pancreatitis or malignancy within the annulus requires it. It is not the operation for uncomplicated annular pancreas.
Recovery
After bypass surgery, recovery reflects the extent of the procedure. Infants typically feed within several days and do well long-term. Adults undergoing duodenojejunostomy usually stay in hospital around five to seven days, returning to normal activity within a few weeks. Symptom relief is generally good when obstruction was genuinely the cause of the symptoms.
Follow-up
Routine follow-up confirms relief of obstruction and adequate nutrition. In children, associated anomalies dictate longer-term care. In adults, no specific surveillance of the pancreas is required unless pancreatitis has occurred.
When to seek a specialist opinion
Any adult with persistent postprandial vomiting, early satiety or unexplained weight loss needs investigation, and annular pancreas is one of several causes of duodenal narrowing — with malignancy being the one that must not be missed. An incidental report of annular pancreas in someone eating normally requires reassurance rather than intervention, and the decision to operate rests on whether symptoms are genuinely attributable to the obstruction, assessed individually.
Common questions
What is annular pancreas?
A ring of pancreatic tissue encircling the duodenum, formed before birth when part of the developing pancreas failed to rotate normally and instead wrapped around the intestine. It is uncommon, and it may cause no trouble at all or may narrow the duodenum enough to obstruct it.
Why do some people present as babies and others only in adulthood?
Because it depends on how tightly the ring constricts the duodenum. A tight ring obstructs from birth and presents in the newborn period with vomiting and feeding difficulty. A looser ring may cause no problem for decades, only becoming apparent in adult life as the tissue becomes inflamed, fibrotic or associated with ulceration, gradually narrowing the passage.
Is it associated with other conditions?
In infants, yes — it is associated with Down syndrome, other intestinal atresias, malrotation and cardiac abnormalities, so a baby diagnosed with it is assessed for these. In adults presenting for the first time, associated abnormalities are much less common.
Does the ring need to be removed?
No, and this is an important point. The ring is not divided or removed, because doing so risks injuring the pancreatic duct running through it and causing a pancreatic leak or pancreatitis. Instead the obstruction is bypassed, leaving the ring untouched.
What does the operation involve?
Joining the duodenum above the obstruction to the duodenum below it, or to a loop of small intestine, so that food passes around the narrowed segment. It is a well-established operation with good long-term results, and in adults it can often be performed laparoscopically.
Will my digestion be normal afterwards?
Yes, in the great majority. The pancreas itself is left intact and continues to function normally, and food simply takes a slightly different route past the narrowed section. Most people eat an unrestricted diet afterwards.
Could my symptoms have been something else?
In adults, yes, and this should be checked. Peptic ulcer disease, gastric outlet obstruction from other causes, and tumours of the duodenum or pancreatic head can all produce a similar picture, and an endoscopy with biopsies is part of the assessment before attributing symptoms to the ring.
Does it increase the risk of anything later?
There is an association with peptic ulceration and with pancreatitis in the encircling tissue, and rare reports of tumours arising in it. This is why persistent or changing symptoms after diagnosis are investigated rather than assumed to be from the known abnormality.
Related conditions
Other conditions of the pancreas covered on this site:
- Pancreatic ductal adenocarcinoma
- Acute pancreatitis
- Chronic pancreatitis and its complications
- Pancreatic cysts — IPMN and MCN
- Pancreatic neuroendocrine tumours
- Solid pseudopapillary neoplasm and other rare pancreatic tumours
- Periampullary lesions
- Pancreas divisum
This page provides general information and does not replace an individual medical consultation. Assessment and treatment are decided for each patient after review of their history, examination and imaging.