Sphincter of Oddi Manometry

The sphincter of Oddi (SO) is a complex smooth muscle structure surrounding the terminal common bile duct, main pancreatic duct, and the common channel, when present ( Fig. 16.1 ). The high-pressure zone generated by the sphincter ranges from 4 to 10 mm in length. The SO regulates the flow of bile and pancreatic exocrine juice and prevents duodenum-to-duct reflux (i.e., maintains a sterile intraductal environment). The SO possesses a basal pressure and phasic contractile activities; the former appears to be the predominant mechanism regulating flow of pancreatobiliary secretions. Although phasic SO contractions may aid in regulating bile and pancreatic juice flow, their primary role appears to be maintaining a sterile intraductal milieu.

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A–D, Schematic representation of the sphincter of Oddi, demonstrating the circular smooth muscle that surrounds the common channel, distal common bile duct, and pancreatic duct.

Sphincter of Oddi dysfunction (SOD) refers to an abnormality of SO contractility. It is a benign noncalculous obstruction to the flow of bile or pancreatic juice through the pancreatobiliary junction (i.e., the SO). This may cause pancreaticobiliary-type pain, cholestasis, and/or recurrent pancreatitis. The most definitive development in our understanding of the pressure dynamics of the SO came with the advent of sphincter of Oddi manometry (SOM). SOM is the only available method to measure SO motor activity directly. SOM is considered by most authorities to be the most accurate means to evaluate patients for sphincter dysfunction. Although SOM can be performed intraoperatively and percutaneously, it is most commonly performed endoscopically at the time of endoscopic retrograde cholangiopancreatography (ERCP). The use of manometry to detect motility disorders of the SO is similar to its use in other parts of the gastrointestinal tract. However, performance of SOM is more technically demanding and hazardous, with adverse event rates (in particular, pancreatitis) approaching 20% in several series. Its use therefore should be reserved for patients with clinically significant or disabling symptoms. Other noninvasive and provocative tests designed to diagnose SOD have therefore been evaluated. Secretin-stimulated endoscopic ultrasonography and magnetic resonance cholangiopancreatography (MRCP) have low sensitivity and specificity for the diagnosis of SOD. Furthermore, nuclear cholescintigraphy, once advocated as an alternative noninvasive test of choice, has led to disappointing results. One needs to appreciate, however, that SOM is not likely an independent risk factor for post-ERCP pancreatitis when the aspirating manometry catheter is used (see section, “Equipment”). Questions remain as to whether the short-term observations (2-minute to 10-minute recordings per pull-through) reflect the “twenty-four-hour pathophysiology” of the sphincter. Despite these problems and lingering doubts as to its clinical utility, SOM has gained more widespread application after 3 decades of evaluation. In this chapter, we will discuss the technique of SOM, with an emphasis on the technical and cognitive skill sets required.