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Gastrointestinal Imaging |
1 From the Departments of Radiology (R.M., M.G.B., S.S., G.M., A.V., P.M.) and Surgery (G.C., M.M.), A. Gemelli University Hospital, 8 Largo A. Gemelli, Rome, Italy 00168. From the 1999 RSNA scientific assembly. Received December 3, 1999; revision requested December 30; revision received February 14, 2000; accepted February 23. Address correspondence to R.M. (e-mail: rmanfredi@rm.unicatt.it).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: One hundred seven patients suspected of having pancreatic disease underwent MRCP before and after secretin administration (S-MRCP). S-MRCP images were evaluated for pancreas divisum and santorinicele and for size of the main pancreatic duct and santorinicele. The onset of duodenal filling was calculated on dynamic S-MRCP images.
RESULTS: Pancreas divisum was detected in five (5%) of 107 patients at MRCP and in 10 (9%) of 107 patients at S-MRCP. Santorinicele was detected in three (21%) of 14 patients at MRCP and in an additional four (seven [50%] of 14) patients at S-MRCP in patients with pancreas divisum. Santorinicele was confirmed in six of seven patients at endoscopic retrograde cholangiopancreatography (ERCP); in one of seven patients, ERCP was unsuccessful. The duct of Santorini was significantly (P < .05) larger in the pancreatic head in patients with pancreas divisum and santorinicele (3.6 mm) compared with those with only pancreas divisum (2.2 mm). A noteworthy reduction in size of the pancreatic duct (26%) and of the santorinicele (63%) was observed after sphincterotomy. The onset of duodenal filling was delayed significantly in patients with santorinicele (2.1 vs 1.3 minutes; P < .05).
CONCLUSION: S-MRCP helps in identifying pancreas divisum and santorinicele, which may be the cause of impeded pancreatic outflow.
Index terms: Endoscopic retrograde cholangiopancreatography (ERCP), 770.1222 • Magnetic resonance (MR), cholangiopancreatography, 770.121411, 770.121412, 770.121415 • Magnetic resonance (MR), comparative studies, 770.121411, 770.121412, 770.121415, 770.1222 • Pancreas, function • Pancreas, MR, 770.121411, 770.121412, 770.121415 • Pancreatic ducts, MR, 774.121411, 774.121412, 774.121415 • Pancreatitis, 770.291 • Secretin
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Cystic dilatation of the distal dorsal duct, just proximal to the minor papilla, termed "santorinicele," which is analogous to ureteroceles and choledochoceles, is believed to result from a combination, either acquired or congenital, of relative obstruction and weakness of the distal ductal wall (7). Furthermore, the santorinicele has been suggested as a possible cause of relative stenosis of the accessory papilla (8), which in association with unfused dorsal and ventral ducts results in the high intraductal pressure responsible for recurrent episodes of acute pancreatitis.
Magnetic resonance (MR) cholangiopancreatography (MRCP) is an imaging technique that noninvasively depicts biliary and pancreatic ducts (9–12); furthermore, dynamic MRCP of the pancreatic duct can be performed after secretin stimulation (13–16). This technique improves depiction of pancreatic ducts and may be effective in diagnosing the presence of santorinicele in patients who have pancreas divisum and unexplained recurrent episodes of acute pancreatitis and who might benefit from endoscopic treatment.
The aim of our study was to evaluate the usefulness of MRCP before and after secretin administration in diagnosing santorinicele in patients with pancreas divisum; we emphasized the possible role of dynamic S-MRCP in evaluating pancreatic fluid egression through the minor papilla.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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None of the patients showed a lesion occupying space within the pancreatic parenchyma or ductal alteration at ultrasonography (US; 107 patients) and/or computed tomography (CT; 26 patients). Biliary pancreatitis was excluded by means of laboratory data findings, during the acute episodes, and the absence of gallstones and choledocholithiasis at US and/or CT. Five patients had previously undergone cholecystectomy; one, a Billroth II procedure; and one, sphincterotomy of the major papilla, all at another institution.
The subjects were asked to fast for at least 4 hours before examination. The study was approved by the hospital review board, and written informed consent was obtained from all patients.
Thirty-eight of 107 patients underwent endoscopic retrograde cholangiopancreatography (ERCP; mean, 10 days after MRCP/S-MRCP; range, 0–173 days). During ERCP, sphincterotomy of the major papilla was performed in nine of 38 patients, whereas sphincterotomy of the minor papilla was performed in six of 38 patients. Twenty-three of 38 patients did not undergo any endoscopic treatment during ERCP.
Follow-up S-MRCP after sphincterotomy was performed in three patients (mean, 283 days after ERCP; range, 4–499 days). S-MRCP findings were compared with the ERCP findings that represented the standard of reference of diagnosis in our study.
MRCP Studies
The MR studies were performed with a 1.5-T clinical imager (Horizon Echospeed; GE Medical Systems, Milwaukee, Wis), with use of a phased-array surface coil and commercially available software (GE Medical Systems). Coronal T2-weighted images of the pancreas were obtained by using half-Fourier rapid acquisition with relaxation enhancement (single-shot fast spin-echo) and the following parameters: 
/110 (repetition time msec/echo time msec); matrix, 256 x 256; one-half of a signal acquired; section thickness, 6 mm; intersection gap, 1 mm; field of view, 40 cm.
A transverse T1-weighted spoiled gradient-echo pulse sequence, without and with fat saturation, was used subsequently in the pancreas. Imaging parameters were as follows: 160/4.2; flip angle, 90°, section thickness, 6 mm; intersection gap, 1 mm; matrix, 256 x 192; one signal acquired; field of view, 30 cm.
Transverse T2-weighted imaging was performed with half-Fourier rapid acquisition with relaxation enhancement and the following parameters: /110; matrix, 256 x 256; one-half of a signal acquired; section thickness, 6 mm; intersection gap, 1 mm; field of view, 30 cm. Heavily T2-weighted MRCP was performed along the coronal plane by using breath-hold two-dimensional half-Fourier rapid acquisition with relaxation enhancement. Parameters were as follows: /800; section thickness, 35–45 mm; matrix, 256–512 x 256; one-half of a signal acquired; field of view, 26–32 cm; total acquisition time, 2 seconds. No postprocessing was performed.
To eliminate overlapping fluid-containing organs, a negative contrast agent, ferumoxsil (Lumirem; Guerbet, Roissy, France), which consisted of 200 mL of superparamagnetic iron oxide particles, was administered orally before dynamic imaging.
A set of MRCP images was obtained before secretin administration to optimally position the image section, which included the entirety of the pancreatic ducts and their emergence in the papillae. After intravenous administration of secretin (Sekretolin, Hoechst, Frankfurt am Main, Germany; or Secrelux, Goldham-Bioglan, Zusmarhausen, Germany) in a dose of 1 clinical unit per kilogram of body weight, the optimal MRCP section was repeated every 30 seconds. In this manner, the pancreatic fluid entering the duodenum could be identified easily on dynamic S-MRCP images. The dynamic procedure was conducted during 10 minutes, and the overall examination time was 25–30 minutes.
Image Analysis
MRCP images were analyzed by two radiologists (R.M., M.G.B.) with experience in hepatic, biliary, and pancreatic imaging and without knowledge of the clinical data or ERCP results. Analysis was performed retrospectively and in a randomized fashion. For each patient, images obtained before and after administration of secretin were evaluated together for comparison; differences in interpretation were settled by means of consensus.
Qualitative image analysis.—Images were evaluated for the presence of pancreas divisum and of santorinicele. All evaluations were performed by using images obtained before and after administration of secretin.
Quantitative image analysis.—This included the size of the main pancreatic duct, in the head, body, and tail of the pancreas, and of the santorinicele before and 1, 3, 5, and 10 minutes after administration of secretin. The maximum size of the dorsal pancreatic duct and of the santorinicele were measured at follow-up S-MRCP in those patients who underwent sphincterotomy of the minor papilla. All measurements were performed on a workstation with an electronic caliper by a radiologist (S.S.) who did not perform the qualitative analysis.
The pancreatic fluid outflow was evaluated on the image time series by three radiologists (R.M., M.G.B., S.S.); namely, the onset of duodenal filling was calculated in the two groups of patients on dynamic S-MRCP images. When the physiologic duodenal fluid was not suppressed by the negative contrast agent, the increase in signal intensity was measured in the descending portion of the duodenum and in the duodenal bulb.
ERCP images were interpreted in a randomized fashion by an expert (G.C.) in biliary and pancreatic imaging. The presence of pancreas divisum and santorinicele was recorded. Pancreas divisum was diagnosed on the basis of the cannulation of both the major and minor papilla and filling of the respective ductal systems.
Statistical Analysis
A one-tailed Student t test was used to calculate the difference in the maximum diameter of the dorsal pancreatic duct at different time points in the group of patients with pancreas divisum and santorinicele versus that in the group of patients with pancreas divisum without santorinicele. Furthermore, a one-tailed Student t test was used to calculate the difference in the onset of duodenal filling between the group of patients with pancreas divisum and santorinicele and the group with pancreas divisum without santorinicele.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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During the past 2 decades, the extensive use of ERCP has permitted the evaluation of the prevalence of pancreas divisum in selected populations and has shown the prevalence to be in the range of 1.3%–6.7% (3,17). This is somewhat lower compared with that from an autopsy series (19), which ranges from 4% to 14%.
MRCP is able to depict the pancreatic ducts noninvasively, and pancreas divisum was diagnosed in six (16%) of 37 patients by using a non-breath-hold three-dimensional fast spin-echo pulse sequence and a body coil, with two false-positive results (9), and in 25 (9.3%) of 268 patients by using transverse images and a phased-array multicoil (12). In our series, pancreas divisum was depicted on MRCP images in five (5%) of 107 patients and on S-MRCP images in 10 more patients, for a total 15 (14%) of 107 patients (Table; Fig 1). This result is in the range of that reported for an autopsy series (19). However, in our series there was also one false-positive result; one pancreas divisum diagnosed at MRCP was a normally fused pancreas at ERCP, with a small reduction in the size of the ventral duct at the junction with the dorsal duct, which suggests a dominant dorsal ductal syndrome (Table). This is due to the substantially higher spatial resolution of ERCP, compared with that of MRCP, which enables depiction of minute communications between the two ductal systems.
One limitation of our study was that in only 12 of 15 patients with pancreas divisum could S-MRCP images be correlated with ERCP images; therefore, we might have other false-positive results in the three patients with diagnosis of pancreas divisum at MRCP who did not undergo ERCP. Furthermore, overall only 38 of 107 patients underwent ERCP; therefore, the accuracy of S-MRCP in the diagnosis of pancreas divisum may be impaired by the possibility of false-negative results—diagnoses not found at S-MRCP but possibly present at ERCP.
Santorinicele was detected in three patients at MRCP and in seven patients at S-MRCP (Table; Figs 2, 3). All patients with santorinicele underwent ERCP, and the diagnosis was confirmed in six of seven patients; in one patient, however, the minor papilla could not be cannulated because a Billroth II procedure had been performed.
Santorinicele is believed to result from a combination of obstruction and weakness of the distal ductal wall. Four cases of santorinicele detected at ERCP were described by Eisen et al (8), which suggests that santorinicele may be the cause of impeded egression of pancreatic secretions via the dorsal ductal orifice. Individual attacks of recurrent acute pancreatitis may be caused by temporary obstruction of the minor papilla during the passage of protein aggregates, which leads to increased intraductal pressure (5,8), when santorinicele occurs in patients with pancreas divisum, as happened in all of the patients in our series.
Secretin stimulates the exocrine pancreatic parenchyma, which leads to accumulation of fluid and bicarbonates within the pancreatic ducts. This effect increases the amount of protons, the source of MR signal, within the ducts and enlarges the pancreatic ducts (13–16), which improves depiction of the pancreatic ducts. In our series, secretin increased the size of pancreatic ducts (Fig 4). Furthermore, the size of the main pancreatic duct in the head of the gland (Fig 4) was significantly larger in patients with pancreas divisum and santorinicele compared with those with pancreas divisum without santorinicele, which most likely suggests the presence of impeded pancreatic secretion outflow at the level of the minor papilla, with subsequent increased intraductal pressure (5).
The hypothesis of increased pancreatic outflow is further sustained by the remarkable reduction in size of the main pancreatic duct and of the santorinicele on follow up S-MRCP images obtained in patients who underwent sphincterotomy of the minor papilla (Fig 5). Of note also is the fact that the patients who underwent endoscopic sphincterotomy also had clinical improvement with remission of symptoms.
A significant delay in duodenal filling after the administration of secretin in patients with pancreas divisum and santorinicele compared with those with only pancreas divisum may also be explained by the impeded pancreatic secretion outflow secondary to stenosis of the accessory papilla, with subsequent increased intraductal pressure (5). Therefore, this group of patients may benefit from endoscopic papillotomy or sphincteroplasty of the minor papilla, as suggested by some authors (20) (Fig 3).
In conclusion, pancreas divisum most likely should not be considered a morbid condition by itself; to cause disease, there must be an additional factor, such as santorinicele, that impedes pancreatic secretion outflow (21) and increases intraductal pressure (5). Identifying the subset of patients with pancreas divisum and pancreatitis who may benefit from therapeutic intervention is a formidable task that MRCP is able to help perform after secretin stimulation because of its capacity as a noninvasive functional examination.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, P.M.; study concepts and design, G.C., R.M.; definition of intellectual content, G.C.; literature research, S.S.; clinical studies, M.M., G.C., R.M.; data acquisition, R.M.; data analysis, R.M., S.S., M.G.B.; statistical analysis, R.M.; manuscript preparation and editing, R.M.; manuscript review, A.V., G.M.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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; n = 8) and those with pancreas divisum without santorinicele (
; n = 7).
= patient 6.