Annular Pancreas: Symptoms, Types, Causes and Treatment

Annular pancreas is a rare congenital anomaly where a ring of pancreatic tissue encircles the duodenum, potentially leading to a spectrum of digestive symptoms and complications across the lifespan. While often detected in newborns because of intestinal obstruction, it can remain silent until adulthood and appear incidentally on imaging. Understanding its symptoms, anatomical types, causes, and treatment options is crucial for timely diagnosis and effective care. In this article, we provide a comprehensive overview of annular pancreas, drawing from current research and clinical experience.

Symptoms of Annular Pancreas

Annular pancreas may not always cause symptoms. When it does, the manifestations differ between infants, children, and adults, and can range from mild discomfort to life-threatening obstruction. Recognizing the varied clinical presentations is essential for prompt diagnosis and management.

Age Group	Common Symptoms	Less Common Symptoms	Sources
Newborns	Vomiting (often nonbilious), feeding intolerance	Abdominal distension, failure to thrive	1, 3, 12
Children	Vomiting, partial/complete duodenal obstruction	Chromosomal/congenital anomalies	3, 1
Adults	Abdominal pain, nausea, vomiting, pancreatitis, duodenal obstruction	Peptic ulcers, obstructive jaundice, incidental finding	2, 4, 5, 6, 11, 13, 14

Table 1: Key Symptoms

Newborns and Children

Infants typically present within the first week of life, often with persistent vomiting that is usually nonbilious, reflecting obstruction above the ampulla of Vater. Feeding intolerance and abdominal distension may also be seen. In severe cases, failure to thrive and dehydration can develop rapidly, necessitating urgent intervention. Annular pancreas in children frequently coexists with other congenital anomalies, such as intestinal malrotation or chromosomal disorders like Down syndrome, although the association with trisomy 21 is weaker than with other duodenal atresias 1, 3.

Adults

In adults, annular pancreas may remain asymptomatic and only be discovered incidentally during imaging for other reasons 4. When symptoms do occur, they are often nonspecific and may mimic other gastrointestinal disorders:

• Abdominal pain is the most common symptom.
• Nausea and vomiting may reflect intermittent or chronic duodenal obstruction.
• Recurrent pancreatitis can arise when the encircling tissue impedes pancreatic drainage.
• Peptic ulcer disease and gastrointestinal bleeding may result from chronic obstruction and stasis.
• Obstructive jaundice is rare but can occur if the annulus constricts the bile duct 2, 4, 11, 14.

The duration of symptoms in adults can range from weeks to years, and the diagnosis is frequently delayed due to the non-specific nature of complaints and the rarity of the condition 2, 14.

Variable Severity and Diagnostic Clues

The severity of symptoms depends on the degree of duodenal narrowing. Some individuals cope with partial obstruction for years, reporting only intermittent symptoms such as vomiting after large meals or intolerance to solid foods 12. Radiological signs, like the classic "double bubble" appearance on abdominal X-rays, may provide clues, especially in neonates 12.

Types of Annular Pancreas

Annular pancreas is not a uniform entity; it can vary in both anatomical configuration and clinical significance. Understanding these variations helps guide diagnosis and treatment planning.

Type Name	Description	Clinical Relevance	Sources
Complete Annular	Full ring of pancreatic tissue encircles the duodenum	More likely symptomatic	6, 7, 12, 14
Partial Annular	Incomplete ring; tissue partially surrounds duodenum	May be asymptomatic or mild symptoms	12, 13, 14
Ductal Types	Divisional, branch, or main duct fusion patterns	Impacts imaging and diagnosis	7
Portal Annular	Pancreatic tissue encircling the portal vein or SMV	Surgical relevance; risk of complications	9, 10

Table 2: Types of Annular Pancreas

Classic (Duodenal) Annular Pancreas

The most widely recognized type is the classic annular pancreas, where a ring of pancreatic tissue, either complete or partial, surrounds the second (descending) portion of the duodenum.

• Complete annulus is more likely to cause symptoms, especially in newborns and children, due to a tighter constriction 6, 12.
• Partial annulus may be overlooked, as some duodenal passage remains, potentially delaying diagnosis until adulthood 12, 13, 14.

Ductal Variants

Based on the fusion pattern of pancreatic ducts, annular pancreas can be further classified into:

• Type I (Divisional): The annular duct drains separately from the main duct.
• Type II (Branch): The annular tissue drains via small branches into the main duct.
• Type III (Main Duct): The annular duct fuses to form part of the main pancreatic duct.

These ductal variants mainly impact imaging interpretation and the risk of complications during surgical or endoscopic interventions 7.

Portal Annular Pancreas

A recently recognized anatomical subtype is the portal annular pancreas (PAP), where pancreatic tissue encircles the portal vein or superior mesenteric vein rather than the duodenum 9, 10. While PAP does not typically cause gastrointestinal symptoms, it is of great importance to surgeons performing pancreatic resections due to the increased risk of postoperative pancreatic fistula and other complications if not identified preoperatively 9, 10.

Clinical Implications

• Complete annular pancreas is more often symptomatic in childhood.
• Partial forms may only become clinically evident in adulthood or remain undetected.
• Ductal and portal variants are important for surgical planning and avoiding intraoperative complications.

Causes of Annular Pancreas

Annular pancreas is a congenital anomaly, meaning it develops before birth. The underlying causes relate to errors in embryonic development, but genetic and environmental factors may also play a role.

Etiology	Description	Notes	Sources
Embryological	Incomplete rotation/fusion of ventral and dorsal pancreatic buds	Main cause; occurs during fetal life	6, 7, 12, 14
Genetic Factors	Possible association with chromosomal anomalies	Often seen with other congenital malformations	1, 3
Environmental	Not well defined	Unclear contribution	3

Table 3: Causes of Annular Pancreas

Embryological Development

The normal pancreas forms from two buds—dorsal and ventral—emerging from the primitive foregut. As the duodenum rotates during embryogenesis, the ventral bud usually moves behind the duodenum to fuse with the dorsal bud, forming the head of the pancreas. In annular pancreas, this process goes awry:

• The ventral bud splits into right and left components.
• If the left ventral bud persists (instead of regressing), it migrates in the opposite direction, wrapping around the duodenum and forming a ring of pancreatic tissue 6, 7, 12.
• Alternative theories suggest abnormal adherence or rotation of the right ventral bud may also result in the annular formation 12.

Genetic and Congenital Associations

Annular pancreas often coexists with other congenital anomalies, including:

• Intestinal malrotation
• Duodenal atresia or stenosis
• Trisomy 21 (Down syndrome)
• Cardiac malformations
• Meckel’s diverticulum 1, 3

While these associations suggest a possible genetic component, no specific causative genes have been identified. The condition appears sporadically in most cases.

Environmental Factors

There is currently no clear evidence of environmental factors contributing directly to the development of annular pancreas. The rarity of the condition and its sporadic presentation limit the identification of external risk factors 3.

Treatment of Annular Pancreas

The management of annular pancreas depends on the patient’s age, the severity of symptoms, and whether complications such as duodenal obstruction, pancreatitis, or peptic ulceration have developed.

Patient Group	Indications for Treatment	Preferred Approach	Sources
Newborns/Children	Symptomatic obstruction	Duodenoduodenostomy bypass	1, 3, 12, 14
Adults	Obstruction, persistent symptoms	Gastrojejunostomy, duodenojejunostomy, endoscopic intervention	2, 5, 14
All	Asymptomatic, incidental finding	Observation, no treatment needed	4, 6
Portal Annular	Undergoing pancreatic surgery	Careful preoperative planning to avoid fistula	9, 10

Table 4: Treatment Strategies

Newborns and Children

Surgical bypass is the standard of care for infants and children with symptomatic duodenal obstruction:

• Duodenoduodenostomy is the most commonly performed procedure. It creates a direct connection between two segments of the duodenum, bypassing the obstructed segment 1, 3, 12, 14.
• Occasionally, duodenojejunostomy or other modifications may be used if the anatomy is complex or associated anomalies are present 1, 3.
• Direct resection of the annular tissue is avoided due to the risk of damaging the pancreatic or biliary ducts, leading to pancreatitis or fistula formation 12, 14.

Prognosis after surgery is excellent, with most patients tolerating feeds within days and being discharged in good health 3.

Adults

Treatment is tailored to the individual's symptoms and the degree of obstruction:

• Surgical bypass (gastrojejunostomy or duodenojejunostomy) is preferred for significant obstruction 2, 5, 14.
• In select cases, especially when symptoms are mild or intermittent, endoscopic interventions (such as sphincterotomy or stenting) may be effective 2.
• Resection of the annular tissue is generally avoided unless there is a strong suspicion of malignancy or associated chronic pancreatitis 6, 14.
• If an incidental annular pancreas is found during imaging or surgery in an asymptomatic adult, no treatment is necessary 4, 6.

Portal Annular Pancreas

This anatomical variant does not usually require treatment unless the patient is undergoing pancreatic surgery. In such cases:

• Careful preoperative imaging (including MRCP) is crucial to identify the variant.
• Surgical techniques are adjusted to minimize the risk of postoperative pancreatic fistula, a major complication in this group 9, 10.

Complications and Follow-up

Postoperative complications are uncommon when proper surgical technique is used, but may include:

• Anastomotic leak
• Pancreatitis
• Bile duct injury
• Recurrent obstruction, especially if fibrosis develops at the anastomosis site 14

Long-term outcomes are generally favorable. Patients with underlying genetic or congenital syndromes may require multidisciplinary follow-up 3.

Conclusion

Annular pancreas is a rare but clinically significant congenital anomaly. Its manifestations span from severe neonatal duodenal obstruction to subtle or asymptomatic presentations in adults. Early recognition and appropriate surgical intervention offer excellent outcomes.

Key Points:

• Annular pancreas may cause vomiting and obstruction in newborns, and abdominal pain or pancreatitis in adults, but can be entirely asymptomatic 1, 2, 3, 4.
• Types include complete and partial annular forms, various ductal fusion patterns, and the portal annular variant with implications for pancreatic surgery 6, 7, 9, 10, 12, 13, 14.
• The primary cause is an embryological error in pancreatic bud rotation, sometimes associated with other congenital anomalies 6, 7, 12.
• Surgical bypass is the mainstay of treatment for symptomatic cases; asymptomatic patients require no intervention 1, 3, 4, 14.
• Awareness of the condition, especially in adults with unexplained gastrointestinal symptoms or in those undergoing pancreatic surgery, is essential for optimal care.

By appreciating the diversity of presentations and advances in diagnostic imaging and surgical technique, clinicians can ensure the best outcomes for patients with this remarkable pancreatic anomaly.