Prepared by Maria E. Pace, MD, CT/MR Fellow, and Barry Daly, MD, FRCR, Associate Professor, Department of Radiology, University of Maryland, Baltimore, MD.

PROBLEM:

A 63-year-old female presented with epigastric abdominal pain. Laboratory values demonstrated an amylase of 67, lipase of 2630, and elevated liver function tests. An image from a coronal reformatted single breath-hold magnetic resonance cholangiopancreatogram (MRCP) is shown (figure 1). What is the most likely diagnosis?

DISCUSSION:

The noninvasive radiologic evaluation of biliary tract obstruction has, until recently, been primarily evaluated by CT or ultrasound. While these modalities are useful for determining the presence of obstruction, direct cholangiography or ERCP remains the gold standard, having the highest sensitivity for visualizing biliary tract anatomy and for determining the level of obstruction. However, ERCP is an expensive, invasive procedure which is operator dependent and can be associated with major complications.

MRCP provides a safe, noninvasive alternative to ERCP which can be performed as an out-patient procedure, usually without sedation. MRCP images are rapidly obtained utilizing a heavily T2-weighted sequence which relies on the inherent brightness of fluid to delineate biliary anatomy. Cholangiogram-like images can be obtained by acquiring signal from a single thick slab through the upper abdomen using a prolonged echo time to suppress solid background tissues. Oral contrast agents can also be administered to suppress adjacent bowel signal. In this patient, the slab of data for figure 1 was acquired in a 2-second breath-hold utilizing an EXPRESS fast-spin echo sequence on a 1.5-Tesla MR scanner. This technique virtually eliminates any motion misregistration, as well as increases signal-to-noise ratio and improves spatial resolution. Software that can provide a single-shot acquisition is available on some MR systems. Such techniques include the single-shot fast-spin echo (SSFSE) sequence and its counterpart, half-Fourier single-shot turbo-spin echo (HASTE) acquisition.

The role of MRCP is broad. It can be used as a primary diagnostic cholangiography and pancreatography study. In cases of failed or incomplete ERCP, MRCP can be used to delineate biliary tree anatomy, both proximal and distal to the level of obstruction. Additionally, MRCP can be used in conjunction with T2-weighted and gadolinium-enhanced gradient dynamic, or fat-saturated SE T1-weighted sequences of the liver and pancreas to determine the cause of obstruction, as well as to identify the extent of local and metastatic liver spread in the setting of malignant obstruction. MRCP allows the determination of patients who need biliary drainage and the selection of the most appropriate route--either via ERCP or percutaneous intervention. Fulcher et al demonstrated an accuracy of 98.2% for the diagnosis of malignant obstruction utilizing MRCP. In that study, use of MRCP obviated the need for ERCP by excluding biliary stones in 95 of 300 patients (32%) with undiagnosed abdominal pain or acute pancreatitis.

Recent studies of the MRCP diagnosis of choledocholithiasis are favorable, with sensitivity ranging from 81 to 100% and specificity ranging from 97 to 100% for the detection of biliary stones. Biliary stones appear black on the background of bright/white bile. This is compared to ERCP data, published by Frey et al, which report a sensitivity of 90.4% and a specificity of 98% in the detection of choledocholithiasis.

MRCP also can be used to assess variant and postoperative biliary anatomy, acute or chronic pancreatitis, and cholangitis.

The disadvantages of MRCP compared to ERCP include the inability to biopsy tissues, the inability to perform a therapeutic role (such as stent placement or endoscopic sphincterotomy), and slightly diminished image resolution.

Overall, the role of MRCP is increasing as a reliable and sensitive exam that can perform a rapid acquisition, yielding diagnostic information comparable to that of ERCP.