Sphincter of Oddi Dysfunction (SOD)
The sphincter of Oddi is the muscular valve surrounding the exit of the bile duct and pancreatic duct into the duodenum, at the papilla of Vater. The sphincter is normally closed, opening only in response to a meal so that digestive juices can enter the duodenum and mix with food for digestion.
The mechanism of Sphincter of Oddi dysfunction is not completely known but, in theory, when an individual has SOD, his/her sphincter goes into "spasm", causing temporary back-up of biliary and pancreatic juices, resulting in attacks of abdominal pain.
Sphincter of Oddi dysfunction refers to two conditions that can affect the sphincter of Oddi – papillary stenosis and biliary dyskinesia.
Papillary stenosis is a condition that occurs when this sphincter (opening) mechanism is disturbed. When the hole is too tight, there is a backup of bile and pancreatic juices which can result in abdominal pain and/or jaundice. Also, blockage to the pancreatic orifice can cause pancreatic pain or attacks of pancreatitis.
Biliary dyskinesia is a gallbladder dysfunction where the biliary ducts fail to contract properly and/or a reduction in the speed of emptying of the biliary tree occurs. Often a symptom rather than a disease itself, biliary dyskinesia might signal the existence of other digestive disorders such as acute or chronic pancreatitis, chronic inflammation or gallbladder stones.
The experience of having SOD is unforgettable. Pain symptoms of SOD are very similar to those caused by bile duct or gallbladder stones. Indeed, sphincter of Oddi dysfunction most frequently occurs in patients who have previously undergone removal of the gallbladder (cholecystectomy). SOD may be one manifestation of other muscular spasm problems in different areas of the body such as the esophagus or large intestine. However, in some patients, it is the prevailing complaint, and requires immediate attention.
Symptoms of SOD
- abdominal pain
- located in mid- or right-upper abdomen
- might also be felt in the back and shoulders
- can last anywhere from several minutes to several hours
- can be a mild, dull throbbing pain, or ...
- can be so severe that the individual is incapacitated
- prolonged obstruction may result in bile leaking back into the blood stream
- results in abnormalities of the liver function tests
- can result in a yellowish discoloration of the eyes and skin
Diagnosis of SOD
Initially, tests are aimed to make sure that there are no other problems present, such as a stone or small tumor.
Tests may include:
- Standard ultrasound and CT scans are helpful, but not very accurate in detecting or excluding small stones.
- Newer techniques such as MRCP —a special type of MRI scan which mainly highlights the bile ducts and pancreatic ducts— and endoscopic ultrasound are more sensitive and useful.
- Most patients are investigated with ERCP, with Sphincter of Oddi Manometry (SOM).*
* This is only helpful when there is abnormal blood tests and/or MRI or EUS findings of enlarged bile or pancreatic ducts.
For ERCP, a doctor passes a special flexible endoscope down the throat and into the duodenum. This is done under sedation or anesthesia. The purpose of this procedure is to examine the drainage hole of the bile duct at the papilla of Vater. Locating the Sphincter of Oddi is often difficult, as it may be tightly closed, and sits in the folds of the duodenum. Once it is located, dye may be injected into the bile duct and pancreatic duct to double-check for stones and other forms of obstruction.
The possibility of sphincter spasm (dysfunction) is tested during the ERCP by measuring the "squeeze pressure" in the sphincter, with manometry (SOM). SOM is performed only in special referral hospitals. Like all types of ERCP examination, there are risks, particularly the chance of suffering an attack of pancreatitis. For this reason, ERCP in this context is usually done only after other simpler tests have been exhausted.
Treatment of SOD
Treatments may include:
- Mild forms of SOD can be managed by anti-spasm medicines.
- When attacks of pain cause considerable disturbance with life activities, a decision has to be made whether to cut the sphincter (sphincterotomy) during ERCP to either remove stones in the ducts or to improve drainage.
- ERCP is rarely indicacted if gallbladder is not removed.
- When sphincter of Oddi manometry has confirmed that the pressures are high, sphincterotomy gives good relief in more than half of patients.
- The performance of sphincterotomy carries a risk of complications, such as bleeding and perforation, in addition to pancreatitis; the risk of pancreatitis is as high as 20%.
- There is also the possibility of recurrent symptoms after months or years due to scarring of the sphincterotomy.
- Further cutting (repeat sphincterotomy) is sometimes possible, but there are limits; surgical treatment with a transduodenal sphincteroplasty —an open surgery performed under general anesthesia where an incision is made through the first part of the small bowel and the pancreas— may be necessary.
- Transduodenal sphincteroplasty may also be recommended in lieu of ERCP in patients who have undergone previous gastric surgery.
Sphincter of Oddi Dysfunction is a difficult condition, which should be approached and managed with considerable care. Patients may warrant referral to specialist centers, who often have special research protocols.