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 (Figure 28.1). The high‐pressure zone generated by the sphincter varies 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.

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 pancreatobiliary 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 [1, 2]. SOM is considered by most authorities to be the most accurate means to evaluate patients for sphincter dysfunction [3, 4]. Although SOM can be performed intraoperatively [5–7] and percutaneously [8], it is most commonly done in the ERCP setting. 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 complication rates (in particular, pancreatitis) approaching 20% in several series. Its use, therefore, should be reserved for patients with clinically significant or disabling symptoms. 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 “Method of SOM”). Questions remain as to whether the short‐term observations (2‐ to 10‐minute recordings per pull‐through) reflect the “24‐hour pathophysiology” of the sphincter [9–13]. In this review, we will discuss the technique of SOM, with an emphasis on the technical and cognitive skill sets required.

Patient selection

The management and therapeutic approaches of suspected SOD have changed over the years. Historically, SOD has been categorized into three different subtypes for patients with abdominal pain in the post‐cholecystectomy state: SOD I, SOD II, and SOD III [14]. In SOD I, the patient has biliary (or pancreatic) type pain, with elevations in serum liver tests (or pancreatic enzymes) and a dilated common bile duct (or pancreatic duct) on abdominal imaging. In SOD II, the patient has biliary (or pancreatic) type pain, and either elevations in liver tests (or pancreatic enzymes) or a dilated duct. In SOD III, the patient has biliary (or pancreatic) type pain, and neither elevations in liver tests (or pancreatic enzymes) nor dilated ducts. More recently, however, this classification scheme has fallen out of favor, particularly following results of the EPISOD study [15]. This sham‐controlled randomized trial demonstrated no difference in outcomes between SOD III patients undergoing ERCP with sphincterotomy or sham therapy. The Rome IV criteria now refer to SOD I as “sphincter of Oddi obstruction,” SOD II as “functional biliary sphincter disorder,” and SOD III as “functional biliary‐type pain” [16].

Our current practice, and what we believe to be the standard of care, is to perform ERCP with sphincterotomy but without manometry in all patients with suspected SO obstruction (formerly SOD I). For patients with suspected functional biliary sphincter disorder (formerly SOD II), we typically pursue an initial course of medical therapy with antispasmodics and pain modulators. If symptoms are refractory and debilitating, we perform ERCP with manometry on one or both of the biliary and pancreatic sphincters, dictated by the clinical presentation. Patients with biliary‐type pain and elevated serum liver tests or a dilated bile duct may undergo biliary evaluation alone, while patients with unexplained acute pancreatitis may additionally undergo pancreatic manometry. If either sphincter or both are abnormal, we generally perform a biliary endoscopic sphincterotomy, as data have shown similar reductions in recurrent acute pancreatitis in patients with pancreas sphincter dysfunction with either a biliary sphincterotomy or a combined biliary and pancreatic sphincterotomy [17]. In patients with functional biliary‐type pain (previously known as SOD III), we generally treat with medical therapy alone if the supporting evaluation is unrevealing. However, we may consider ERCP with SOM in the patient with recurrent symptoms in whom a prior biliary or pancreatic sphincterotomy has been performed to determine whether sphincter stenosis post‐sphincterotomy has occurred, thus requiring retreatment. Further prospective trials are needed in these difficult‐to‐manage patient categories.

Method of SOM

Equipment

Virtually all standards have been established with size 5 Fr catheters; therefore, these should be used. Triple‐lumen catheters are state of the art and are available from several manufacturers. Catheters with a long intraductal tip may help secure the catheter within the bile duct, but such a long nose is commonly a hindrance if pancreatic manometry is desired. A sleeve catheter is a perfused channel system that records pressure along its length, potentially limiting motion artifacts during performance of SOM [38]. Limited data from Australia suggest that this sleeve method is comparable with standard SOM with triple‐lumen catheters [39], but more data are needed. Over‐the‐wire (monorail) catheters can be passed after first securing one’s position within the duct with a guide wire. Whether this guide wire influences basal sphincter pressure has not been definitively elucidated (see section “Technical performance of SOM”). Some triple‐lumen catheters will accommodate a 0.018‐inch‐diameter guide wire passed through the entire length of the catheter and can be used to facilitate cannulation or maintain position in the duct. Guide wire‐tipped catheters have also being evaluated. Early experience with performance of SOM using perfusion systems demonstrated unacceptably high post‐procedure pancreatitis rates [40–43]. Presumably, overdistension of small caliber pancreatic ducts by the perfusate may lead to this complication. Aspiration catheters (Figure 28.2) in which one recording port is sacrificed to permit both end‐ and side‐hole aspiration of intraductal juice and the perfusing fluid are therefore highly recommended for pancreatic manometry. These catheters have been shown to reduce the frequency of post‐SOM pancreatitis while accurately recording sphincter pressures [42]. Most centers prefer to perfuse the catheters at 0.25 mL/channel/min using a low compliance pump. Lower perfusion rates will give accurate basal sphincter pressure measurements, but will not give accurate phasic wave information. The perfusate generally is distilled water, although physiologic saline needs further evaluation. The latter may crystallize in the capillary tubing of perfusion pumps and must be flushed out frequently. Solid‐state catheters [43, 44] and microtransducer manometry systems [45] are also available and have been used by some investigators in an attempt to avoid volume loading of the biliopancreatic system during perfusion manometry [44]. Preliminary data from a few centers demonstrate comparable SOM results to those achieved with perfusing catheters [43, 45, 46], with a suggestion of a reduction of post‐ERCP pancreatitis in patients undergoing microtransducer manometry[45].

Technical performance of SOM (see accompanying Video 28.1)

SOM requires selective cannulation of the bile duct and/or pancreatic duct. Maximal efficiency is achieved by combining ERCP and SOM in a single session. It is preferable to perform cholangiography and/or pancreatography prior to performance of SOM, as certain findings (e.g., common bile duct stone) may obviate the need for SOM. This can simply be done by injecting contrast media through one of the perfusion ports. Alternatively, the duct entered can be identified by gently aspirating on any port (Figure 28.3). The appearance of yellow‐colored fluid in the endoscopic view indicates entry into the bile duct. Clear aspirate indicates that the pancreatic duct has been entered. This technique may prove useful when attempting to access the bile duct following pancreatic SOM, as repeated pancreatic duct injections may increase post‐ERCP pancreatitis rates [47]. If clear fluid is seen in the catheter, suggesting pancreatic duct entry, the catheter position is altered to achieve a more favorable angle for biliary cannulation. Blaut and colleagues [48] have shown that injection of contrast into the biliary tree prior to SOM does not significantly affect sphincter pressure characteristics. Similar evaluation of the pancreatic sphincter after contrast injection has not been reported. One must be certain that the catheter is not impacted against the wall of the duct in order to ensure accurate pressure measurements. On occasion, selective deep cannulation of the desired duct may only be achieved with a guide wire. However, a study in our unit found that stiffer‐shafted nitinol core guide wires used for this purpose commonly increase basal biliary sphincter pressure measured at ERCP by 50–100% [49]. Therefore, when wire‐guided cannulation is performed, we recommend withdrawing the wire back into the catheter, outside of the duct and not traversing the sphincter, during performance of SOM. Alternatively, stiff guide wires need to be avoided, and very soft‐core guide wires must be used. Once deep cannulation is achieved and the patient acceptably sedated, the catheter is withdrawn across the sphincter at 1‐ to 2‐mm intervals by standard station pull‐through technique. Ideally, both the pancreatic and bile ducts should be studied. Current data indicate that an abnormal basal sphincter pressure may be confined to one side of the sphincter in 35–65% of patients with abnormal manometry [50–55], and thus, one sphincter segment may be dysfunctional and the other normal. Raddawi and colleagues [53] reported that an abnormal basal sphincter pressure was more likely to be confined to the pancreatic duct segment in patients with pancreatitis and to the bile duct segment in patients with biliary‐type pain and elevated liver function tests.

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