My Patient Had a Magnetic Resonance Cholangiopancreatography to Evaluate for Common Bile Duct Stones, but the Reading Includes a “Double Duct Sign.” What Does This Mean? Does It Need Endoscopic Retrograde Cholangiopancreatography?
Although controversial in the past, the current accepted term, double duct sign, refers to narrowing of both the pancreatic and the common bile duct with dilatation of the ducts proximal to the site of narrowing. It is usually discovered through such studies such as magnetic resonance cholangiopancreatography (MRCP) (Figures 39-1 and 39-2), endoscopic retrograde cholangiopancreatography (ERCP), computed tomography (CT) scan (Figure 39-3), and transabdominal or endoscopic ultrasounds (EUS). These studies are usually prompted by obstructive jaundice and other signs and symptoms including abdominal pain, anorexia, abnormal liver function tests, weight lost, cholelithiasis, and choledocholithiasis.
Figure 39-1. Magnetic resonance cholangiopancreatography showing double duct sign: dilatation of both the common bile duct and pancreatic duct from either strictures or external compression.
Figure 39-2. Full-size magnetic resonance cholangiopancreatography of the patient from Figure 39-1.
Figure 39-3. Computed tomography scan of patient with double duct sign.
The significance of double duct sign is its high predictive value for pancreatiobiliary malignancy. In a study by Kalady et al1 of 355 patients, the double duct sign was found to have a sensitivity of 77%, positive predictive value of 65%, specificity of 79.9%, and a negative predictive value of 87.6%. In one Japanese study,2 its positive predictive value can be as high as 80%. Combined with other ductal characteristics, such as severe stenosis and marked proximal dilatations, it is a very useful indicator of malignancies. Benign causes of the double duct sign include chronic pancreatitis, pancreatic pseudocyst, pancreatic duct stones, pancreas divisum, and, in one case report, Strongyloides Stercoralis infection.
The formation of the double duct sign is postulated as a mass at the head of the pancreas or at the ampulla compressing both the distal ends of the common bile duct and pancreatic duct causing an obstruction and dilatation of the ducts. In cases where there is no obvious mass, stricture formation from ductal pancreatic carcinoma or cholangiocarcinoma is felt to be the culprit. In chronic pancreatitis, scar tissue formation in the pancreas causes strictures and dilatation of the ducts. Many studies have been done to look at the size, length, irregularity, and location of the strictures to better differentiate malignant and benign strictures radiologically, although the results are currently inconclusive.3
In general, EUS, helical CT scan, and MRCP/magnetic resonance imaging (MRI) are accurate means for the detection of pancreatic adenocarcinoma and determination of resectability. If the patient is deemed a surgical candidate, ERCP would not be needed. Preoperative ERCP does not add further staging information and may result in complications (pancreatitis, perforation) that may make operative intervention more difficult and/or may considerably delay operative intervention resulting in a decreased potential for curative resection. If an MRCP/MRI or helical CT scan does not reveal an obvious mass or cyst at the head of the pancreas, rather than starting the work-up with ERCP, a less invasive option would be to pursue further evaluation with an EUS with biopsy and fine needle aspiration if a mass can be visualized. This is also a less invasive way to evaluate the ampulla as well.
ERCP serves 2 purposes in a patient with the double duct sign. If no obvious mass is seen on the radiologic study such as MRI or CT scan, the ERCP can be of value. It can serve as a diagnostic tool for tissue confirmation via forceps biopsy, needle aspiration, bile or pancreatic juice aspiration, and brush biopsy for ductal pancreatic carcinoma, however, as noted above this should not be first line.4 ERCP can also be used for confirmation of the diagnosis to guide chemotherapeutic treatment in patients who are not surgical candidates secondary to unresectability and/or co-morbid medical conditions. The sensitivity rate for ERCP-directed brush cytology or biopsy is 30% to 50%, with a combination achieving sensitivity rates of 65% to 70%.5 Techniques to enhance the accuracy of cytology and pancreatic juice appear to be significant, but are experimental or not widely available. The second and most important purpose of ERCP is it can be used for palliation with insertion of metallic or plastic stents for relief of obstructive symptoms from the strictures. In general, the self-expanding metal stents (SEMS) are preferred over the plastic stents if the patient’s life expectancy is greater than 4 months. This is because plastic stents tend to get occluded from bacterial biofilm and have the risk of falling out of the duct. Biliary SEMS offer significantly longer patency rates than 10 French plastic stents. Surgical options have shown to have greater immediate complication rates and a longer initial hospitalization than endoscopic stenting, but provide longer term palliation without the need for intervention. If ERCP is unsuccessful, surgical percutaneous transhepatic cholangiography and stent placement remains an option.6
1. Kalady MF, Peterson B, et al. Pancreatic duct strictures: identifying risk of malignancy. Ann Surg Oncol. 2004;11(6):581-588.
2. Inoue K, et al. Severe localized stenosis and marked dilatation of the main pancreatic duct are indicators of pancreatic cancer instead of chronic pancreatitis on endoscopic retrograde balloon pancreatography. Gastrointest Endosc. 2003;58(4):510-515.
3. Menges M, Lerch MM, Zeitz M. The double duct sign in patients with malignant and benign pancreatic lesions. Gastrointest Endosc. 2000;52:74-77.
4. Rosch T, et al. ERCP or EUS for tissue diagnosis of biliary strictures? A prospective comparative study. Gastrointest Endosc. 2004;60:390-396.
5. ASGE guideline: the role of ERCP in diseases of the biliary tract and the pancreas. Gastrointest Endosc. 2005;62: 1-8.
6. Baron TH, Mallery JS, et al. The role of endoscopy in the evaluation and treatment of patients with pancreaticobiliary malignancy. Gastrointest Endosc. 2003;58:643-649.