What is Annular Pancreas?
An annular pancreas (AP) is a rare birth defect where a band of pancreas tissue partly or completely surrounds the second part of the small intestine, known as the duodenum. Most of the time (about 85% of cases), it’s found above a particular part of the small intestine called the papilla of Vater. It used to be found in about three out of every 20,000 autopsies or 24,519 surgeries. However, now that medical testing has improved, doctors are identifying it more often.
Many people who have this condition do not display symptoms and it might just be found during imaging tests or autopsies. But some patients with an annular pancreas do show symptoms. These symptoms usually start earlier in life or when they’re adults between 20 and 50 years old.
There are two main types of annular pancreas, named for how the pancreatic tissue winds around the duodenum: the complete type and the incomplete type. In the complete type, pancreas tissue fully encloses the duodenum, while in the incomplete type, it only partly wraps it. The annular pancreatic duct, a tube that drains digestive juices from the pancreas, often drains into the main pancreatic duct. But, sometimes it connects up with other ducts like the bile duct or a duct in the pancreas called the duct of Santorini, or another called the duct of Wirsung.
One specific classification of AP, proposed by Yogi and colleagues, divides the condition into six types based on the ducts architecture. The most common types I and II involve the duct of Wirsung and the main pancreatic duct respectively. The four less common types involve the annular pancreatic duct communicating with the duct of Santorini or the common bile duct.
What Causes Annular Pancreas?
An Annular Pancreas (AP) is a rare birth defect that doesn’t have a clearly defined cause. But, it’s generally believed to be an abnormality that happens during the embryonic stage. Usually, in the early weeks of an embryo’s development (4 to 8 weeks), the pancreas is formed from the combination and rotation of two parts, known as the dorsal and ventral buds. The ventral bud becomes the lower part and a section called the uncinate process of the pancreas, whereas the dorsal bud develops into the body and tail of the pancreas.
It’s suggested that the formation of an annular pancreas happens when the ventral bud doesn’t rotate and extend correctly to wrap around a part of the small intestine, the duodenum. As a result, the duodenum can be partially or wholly encased by the pancreas.
Several theories have tried to explain why an annular pancreas forms, dating back to the 1900s, but none has been able to provide an explanation for all cases. Certain studies have suggested that the origin of an annular pancreas could be traced to the ventral pancreatic tissue. While it isn’t well researched, genetic factors might play a role as well, judging from rare reports of families having multiple members with an annular pancreas and conditions where a specific gene called transmembrane 4 superfamily member 3 (tm4sf3) is overly active.
Risk Factors and Frequency for Annular Pancreas
The actual number of cases of annular pancreas, a rare birth defect, is difficult to determine due to its infrequency and underreporting. In the past, this condition was incidentally discovered in 3 out of 20,000 autopsy cases and 3 out of 24,519 patients who underwent abdominal surgeries. Nowadays, with advancements in medical imaging, the reported instances of annular pancreas have increased slightly, with an estimated prevalence of about 1 in 1,000 cases. This condition impacts both males and females, but there seems to be a small bias towards males, though this is a debated point.
Signs and Symptoms of Annular Pancreas
An annular pancreas is a condition that can affect people at any age, from infants to adults. The symptoms can differ based on the patient’s age and the severity of the condition. Infants with an annular pancreas typically display non-bilious vomiting, bloating, and feeding problems. However, those with minimal or no constriction may not show any symptoms for their entire lives. Some individuals can start showing symptoms between their thirties and sixties, which may include abdominal pain, obstruction in the small intestine, and inflammation of the pancreas. Other less common symptoms in adults can be peptic ulcers and biliary obstruction.
People with annular pancreas often have chromosomal abnormalities, with trisomy 21 being the most common. This condition can also be associated with various other birth defects in infants as well as in adults.
- In Infants:
- Malrotation of the intestine
- Tracheoesophageal fistula
- Esophageal atresia
- Small intestinal atresia
- Renal anomalies
- Duodenal diverticulum
- Pancreas divisum
- Biliary atresia
- Anorectal malformations
- Congenital heart disease
- In Adults:
- Pancreatic divisum
- Malrotation of the intestine
- Duodenal webs
- Schatzki ring
Testing for Annular Pancreas
Annular Pancreas (AP) isn’t diagnosed by any specific genetic or biochemical test. The identification of this condition mostly happens incidentally during medical checkups or when assessing the patient’s symptoms associated with AP. Several non-invasive and invasive diagnostic methods can be used to recognize this condition, either before birth, before surgery, or during surgery.
Prenatal ultrasound is one technique that can detect AP in unborn children. For infants showing symptoms of a blocked intestine, ultrasound or plain stomach X-rays can uncover a characteristic “double bubble sign”. However, this sign isn’t exclusively associated with AP.
Medics are now using newer ultrasound methods combined with a saline-contrast gastro-intestinal test to minimize mistakes while diagnosing newborn babies with AP. In adults, the diagnosis of AP is typically made using imaging techniques such as CT (Computerized Tomography) scans or MRI (Magnetic Resonance Imaging).
Besides these, other imaging methods such as Magnetic Resonance Cholangiopancreatography (MRCP), Endoscopic Retrograde Cholangiopancreatography (ERCP), or Endoscopic Ultrasonography (EUS) can aid in diagnosing AP. According to some studies, a full wrap of the duodenum with pancreatic tissue isn’t necessary to confirm AP. Advanced imaging techniques like PET (Positron Emission Tomography) coupled with CT scans and radiotracers have also demonstrated their ability in diagnosing AP.
Despite the advancements in these diagnostic techniques, the most reliable method to diagnose AP remains to be a thorough physical examination of the duodenum and the head of the pancreas during surgery.
Treatment Options for Annular Pancreas
There aren’t currently any set guidelines for managing annular pancreas, a condition affecting the pancreas, so treatment is personalized based on the patient’s symptoms. If a person with annular pancreas doesn’t show any signs or symptoms, doctors may simply monitor them closely rather than intervene.
When patients with annular pancreas show symptoms of acute pancreatitis (an inflammation of the pancreas), supportive care is usually administered. If the patient continues to experience debilitating episodes of pancreatitis, a type of surgical procedure known as a pylorus-preserving Whipple’s procedure may be considered, but this is decided on a case-by-case basis.
Doctors generally avoid a surgical procedure that involves dividing the pancreatic annulus, as it can increase the likelihood of postoperative complications such as pancreatitis, pancreatic fistulas (abnormal connections between the pancreas and other parts of the body), and duodenal stenosis (narrowing of the first part of the small intestine). When the annular pancreas is causing obstructions, surgery that bypasses the duodenum (the first part of the small intestine) is typically done. These surgeries can include procedures such as gastrojejunostomy, duodenoduodenostomy, or duodenojejunostomy and are performed in both children and adults.
The treatment approach can differ between children and adults. A study by Zyromski and colleagues showed that, in contrast to children, 20% of adults with annular pancreas required more complex surgeries. These included procedures like pancreaticoduodenectomy (removal of part of the pancreas), lateral pancreatojejunostomy, sphincteroplasty (widening of the pancreatic or bile ducts), and bypass of the biliary system (rerouting the flow of bile).
What else can Annular Pancreas be?
An annular pancreas (AP) can have symptoms that show up either in babies or adults, which is why doctors consider different causes based on the patient’s age.
Babies with an annular pancreas often have a blockage in the upper part of their small intestine. This is visible as a “double bubble” shape on an imaging scan. Some of the causes for this blockage could come from within the intestine itself, like a narrow or closed-off portion of the intestine, a protrusion called a Meckel diverticulum, or thin walls of tissue known as duodenal webs.
Apart from annular pancreas, some other reasons for the blockage might be related to incorrect positioning or twisting of the gut, known as malrotation or midgut volvulus.
In adults, the diagnosis might consider other diseases like ulcers, pancreatic divisum (a birth defect in which the ducts in the pancreas don’t form properly) or even cancers of the intestine and pancreas. If the patient comes from a region where tuberculosis is common, the doctor might also want to rule out an infection of tuberculosis in the stomach and upper part of the small intestine.
What to expect with Annular Pancreas
The outlook for children with annular pancreas is generally very good and they have high survival rates, even if they have other related birth defects or chromosomal abnormalities. This improved outcome is due to better newborn care practices, the management of their nutrition, early detection, and treatment of associated anomalies. For adults, the outlook is also positive for annular pancreas, as long as it isn’t complicated by cancer.
Possible Complications When Diagnosed with Annular Pancreas
An annular pancreas can lead to several complications. These are usually caused by the shifting or migration of the early forms of the pancreas. The complications can include both acute and chronic inflammation of the pancreas, blockage of the tube that transports bile from the liver to the intestine, peptic ulcers, gallstones, and inflammation of the pancreas. Furthermore, recent research data from large case studies shows an increased incidence of abnormal cell growth or tumor formation in adults with an annular pancreas.
- Acute pancreatitis (Inflammation of the pancreas)
- Chronic pancreatitis
- Common bile duct obstruction (Blockage in the tube moving bile from the liver to the intestine)
- Peptic ulcer disease
- Cholecystolithiasis (Formation of gallstones)
- Pancreatitis (Inflammation of the pancreas)
- Increased risk of abnormal cell growth or tumors
Preventing Annular Pancreas
An annular pancreas is an unusual condition that is present at birth, where a ring of extra pancreatic tissue surrounds the small intestine known as the duodenum. In the past, this anomaly was usually discovered during autopsies or abdominal surgeries. However, with the development of new diagnostic techniques, it is being detected more frequently.
Many people living with this condition don’t show any symptoms. However, it can cause blockage in the intestine in infants and result in symptoms like stomach pain, peptic ulcer disease (stomach ulcers), and pancreatitis (inflammation of the pancreas) in adults. It’s also important to note that this condition is often found in individuals with chromosomal abnormalities, with Down syndrome (trisomy 21) being the most common association.
If a person with an annular pancreas does start to show symptoms, the treatment involves surgery. Doctors perform procedures – such as gastrojejunostomy, duodenoduodenostomy, or duodenojejunostomy – that help to bypass the part of the small intestine that is blocked. These surgeries can be performed on both adults and children.