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Magnetic Resonance Cholangiopancreatography

Is it Becoming the Study of Choice for Evaluating Obstructive Jaundice?

Fulcher, Ann S., MD

Journal of Clinical Gastroenterology: November-December 2004 - Volume 38 - Issue 10 - p 839-840
Editorial
Free

From the Department of Radiology, Virginia Commonwealth University Medical Center, Richmond, VA.

Reprints: Ann S. Fulcher, MD, Department of Radiology, Virginia Commonwealth University Medical Center, Sanger Hall 4-050, Richmond, VA 23298 (e-mail: asfulche@vcu.edu).

Since the introduction of magnetic resonance cholangiopancreatography (MRCP) into the clinical arena in the early 1990s, MRCP has evolved from a technique barely able to depict the biliary tract to an accurate and increasingly widely accepted means of imaging pancreaticobiliary disease. MRCP has been shown to have sensitivities and specificities equal to or approaching those of endoscopic retrograde cholangiopancreatography (ERCP) in the evaluation of choledocholithiasis, neoplastic obstructions, postoperative strictures, primary sclerosing cholangitis, chronic pancreatitis, and congenital anomalies such as choledochal cysts.1-20

MRCP represents an application of MR technology that permits evaluation of the biliary tract, pancreatic duct, and gallbladder without the use of contrast material or instrumentation and thereby avoids the complications of ERCP and percutaneous cholangiography (PTC), such as pancreatitis, bleeding, and perforation. MRCP depicts the pancreaticobiliary tract and gallbladder as high signal intensity or bright structures owing to the fluid within them. The high signal intensity of the ducts provides an optimal background that facilitates the detection of stones, masses, strictures, and other intraluminal or lumen-narrowing abnormalities. The multiplanar capability of MR permits the display of the images in virtually any plane and in three dimensions and thereby allows for the generation images of the pancreaticobiliary tract comparable to those obtained at ERCP and PTC.

MRCP offers several advantages when compared with more invasive techniques used to evaluate the pancreaticobiliary tract such as ERCP and PTC. In addition to the entirely noninvasive nature of MRCP, MRCPs are rapidly acquired such that the entire biliary tract or pancreatic duct can be imaged in less than 20 seconds. Because MRCP is an application of MR technology, patients are not exposed to ionizing radiation.

In this issue of the Journal of Clinical Gastroenterology, Vaishali et al report their experience with MRCP in diagnosing the level and cause of obstruction in 30 patients with obstructive jaundice. Their findings are in agreement with those of other investigators who have found high sensitivities and specificities of MRCP in determining the level and cause of biliary obstruction.1-5 Specifically, they noted an overall diagnostic accuracy for the detection of level and cause of obstruction of 96.3% and 89.65%, respectively.

Vaishali et al correctly diagnosed all causes of obstruction except three. In 1 patient, a small calculus in a nondilated distal bile duct was not identified. Major technical advances in MR and MRCP that have occurred over the past decade have improved the resolution of MRCP such that stones as small as 2 mm can be identified.5 Despite these advances, stones measuring less than 2 mm may go undetected, especially if located in the distal duct or if they occur in the absence of ductal dilatation.

The two other cases in which the cause of obstruction was not correctly diagnosed included focal chronic pancreatitis mistaken for pancreatic head carcinoma and a small pancreatic head carcinoma diagnosed as a distal duct cholangiocarcinoma. These distinctions are often difficult to make even with gross examination of the resected specimens. In many cases, the diagnosis must be made histologically. The preoperative distinction between a small pancreatic head carcinoma and a distal cholangiocarcinoma is primarily academic and of questionable clinical value as both are treated in an identical fashion. It is important to note that Vaishali et al did not perform MRCP in conjunction with a conventional abdominal MR. However, Kim et al found that the addition of conventional MR to MRCP aids in differentiating benign and malignant causes of biliary dilatation.10 In addition, when conventional MR is performed in conjunction with MRCP, a comprehensive examination results that allows not only for evaluation of the ductal systems but also the solid organs and lymph nodes of the abdomen. The importance of this information is underscored in the setting of a malignant cause of biliary obstruction as this comprehensive examination allows not only for diagnosis but also staging.

Although sonography is usually the initial modality used to detect biliary obstruction and detects obstruction in nearly all instances, the diagnosis of obstruction can be made with an accuracy of 90% to 95% with a careful history, physical examination, and serum markers of biliary and hepatic dysfunction.21,22 Despite the ability of sonography to detect obstruction in almost all instances, it assists in the determination of the level and cause of obstruction in only 60% to 92% and 38% to 71% of cases, respectively.23,24

The introduction of helical CT in 1988 and more recent advances in multidetector CT technology have resulted in improved image quality. A study of patients with suspected biliary obstruction performed with helical CT technology showed that the level of obstruction was identified in all but that the cause was correctly diagnosed in only 78%.25 Although multiplanar images of the biliary tract may be rendered with CT cholangiography, this technique requires the intravenous administration of contrast material (iodipamide meglumine), which is excreted by the biliary tract and has been associated with severe systemic effects in approximately 0.02% of patients.26

Prior to the advent of MRCP, direct visualization of the biliary tract and the generation of cholangiographic images were possible only with the performance of invasive examinations such as ERCP and PTC. While these techniques render high resolution images of the ducts and provide an access for therapeutic interventions, they are associated with complications that range in severity from subclinical to life-threatening.

When consideration is given to the various modalities available to evaluate the biliary tract, MRCP particularly when performed in conjunction with conventional MR 1) provides cholangiographic images comparable to ERCP and PTC, 2) yields information about the solid organs comparable to CT and ultrasound (US), and 3) is able to diagnose the presence, level, and obstruction with accuracies superior to those of US and CT and equal to or approaching those of ERCP without placing the patient at risk for complications. It is for these reasons that MRCP has replaced invasive procedures such as ERCP and PTC as a means of diagnosis at many centers and may well obviate the need to perform US and CT. In essence, MRCP and conventional MR may well represent the most efficient means of identifying the presence, level, and cause of obstruction with a single examination.

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