SOM is regarded as the gold standard for the diagnosis of SOD and predicts response to sphincterotomy,23
but it is invasive and associated with complications.3,4,5,6,7
Given the technical difficulties and limited availability of SOM, interest has focused on non‐invasive surrogates for SOM that might identify patients with types II and III SOD likely to benefit from sphincterotomy. In a study using hepatobiliary scintigraphy (HBS) with morphine provocation and a cut‐off value of 15% radionuclide excretion at 60 min, the sensitivity and specificity for detecting raised sphincter of Oddi basal pressures in patients with SOD types II and III were 83% and 81%, respectively.24
In a large retrospective study, Rosenblatt et al25
reported that the combination of fatty meal sonography and HBS was useful in predicting the response to sphincterotomy in patients with manometrically documented SOD. However, some studies have reported a poor correlation between HBS and SOM.26
The use of ss‐MRCP in patients with suspected SOD has been limited. Preliminary data from the Indiana group showed a poor correlation between ss‐MRCP and pancreatic SOM.27,28
By contrast, in a study from Italy29
that included 15 patients with recurrent pancreatitis, ss‐MRCP and SOM were concordant in 13 patients; positive and negative diagnoses for SOD agreed in 82% and 100% of cases, respectively. This study has shown that ss‐MRCP is insensitive in predicting abnormal SOM in patients with type III SOD, but is moderately accurate in the diagnosis of patients with manometrically proved type II SOD, However, ss‐MRCP did correlate well with ERCP in detecting structural changes other than SOD, and emphasises the importance of initial non‐invasive imaging in patients with suspected SOD to exclude other pathologies such as chronic pancreatitis. Additionally, our findings suggest that ss‐MRCP may be useful in selecting patients with suspected SOD II who might benefit from endotherapy.
In this study, we used a duration of ss‐MRCP shorter than described previously,15,27,28,29
because we wanted to explore whether this approach would increase the sensitivity of the examination and improve patients' tolerance of the procedure. To date, ss‐MRCP has been used mainly for the evaluation of the pancreatic segment of sphincter of Oddi. However, secretin also stimulates biliary ductal secretion and increases bile flow.14
Stimulation of secretin receptors on biliary ductal epithelium induces cyclic AMP levels, activation of intracellular cyclic AMP‐dependent protein kinase and opening of cyclic AMP‐dependent channels, which in turn induces a [Cl−
] gradient favouring the activation of the apically located [Cl−
] exchange and resulting in a bicarbonate‐rich choleresis.
Patients with manometrically proved sphincter of Oddi abnormalities may benefit symptomatically from either biliary or pancreatic sphincterotomy, or even dual sphincterotomy. Clinical response varies among the three groups, being highest in biliary types I and II SOD, and lowest in type III SOD.1,25,30
A recent Cochrane review31
concluded that sphincterotomy for biliary SOD was effective for those patients with raised sphincter of Oddi pressures, but no better than placebo for those with normal sphincter of Oddi pressures. Furthermore, pancreatic sphincter hypertension has been described in 15–72% of patients with “idiopathic” recurrent pancreatitis22,27,32
and in some patients whose symptoms fail to improve after biliary endoscopic sphincterotomy.33,34
In patients with persistent symptoms and increased basal pancreatic sphincter pressures, performing a pancreatic sphincterotomy has been associated with an improvement in clinical symptoms in 15–77% of patients.35
In this series, an endoscopic sphincterotomy of the affected segment was performed in all patients with manometrically proved raised sphincter of Oddi pressures. During a mean follow‐up of almost 3 years, there was a marked improvement in pain scores in patients with SOD type II but not in those with SOD type III. This explains, partly, why patients with an abnormal ss‐MRCP, who were diagnosed with SOD type II in 83% of cases, had a considerably higher symptomatic response during follow‐up than those with normal ss‐MRCP.
There are large differences in reported success rates for managing type III SOD between specialist centres. According to a recent systematic review by our group,36
about 37% of such patients report long‐term benefit after sphincter ablation. In this series, patients with SOD type III had a generally poor symptomatic response after endoscopic sphincterotomy of the affected segment. Additionally, these patients have the highest risk of complications of ERCP, principally pancreatitis.37
Based on these results, there is a need for further prospective, controlled trials to justify the invasive management by ERCP and sphincterotomy of patients with SOD type III. The injection of botulinum toxin into the intraduodenal sphincter segment has been reported to predict the long‐term outcome after endoscopic sphincterotomy in patients with manometrically proved biliary type III38
and pancreatic SOD,39
but further studies are needed.
In conclusion, ss‐MRCP is insensitive in predicting abnormal manometry in patients with suspected type III SOD, but is moderately accurate in the diagnosis of patients with SOD type II, who are most likely to benefit from endoscopic sphincterotomy.