Potential role of conventional and contrast-enhanced magnetic resonance cholangiography in the evaluation of the acute abdomen in the emergency setting

Abstract

The imaging evaluation of the acute abdomen in the emergency department usually begins with plain films of the abdomen, although the use of computed tomography (CT) is becoming more prevalent and appropriate. Several studies have shown that CT produces an earlier diagnosis, earlier treatment and improvement in patient care. Furthermore, the use of CT produces a decrease in hospital admissions, unnecessary procedures and cost [1, 2, 3]. Finally, CT is minimally invasive and is readily available, which allows easy scheduling. With the development of rapid magnetic resonance (MR) sequences, torso phased-array coils and stronger gradients, the quality of abdominal MR images has significantly improved over the past decade. Imaging can now be acquired in a breath-hold, with a significant reduction in motion-related artifacts and an increase in contrast and spatial resolution. With the use of modern techniques, MR has been shown to be accurate in the diagnosis of acute appendicitis [4, 5]. Furthermore, Regan et al. demonstrated the accuracy of MR imaging in detecting the presence, location, and cause of small bowel obstruction [6]. However, MR imaging of the acute abdomen is rarely performed in the emergency setting, for several reasons. First, CT can accurately reveal the cause of an acute abdomen in most cases. Second, the literature does not support the use of MR over CT for evaluating the acute abdomen. Third, MR is more expensive than CT. Finally, the limited availability of MR scanners makes it more difficult to schedule an MR imaging study and, as with all new uses of advanced modalities, there is a significant learning curve for interpretation. The greatest potential advantage of abdominal MR imaging over CT in the emergency setting is in the workup of patients with suspected gallbladder and biliary disease. Several studies have demonstrated very good accuracy and greater sensitivity of MR imaging over ultrasound for the diagnosis of acute cholecystitis using fast MR techniques [7, 8]. Since CT is inferior to ultrasound, then MR imaging should be superior to CT for the diagnosis of acute cholecystitis. In addition, even though CT can detect the presence and location of biliary obstruction, it cannot accurately detect the cause of obstruction (stones, strictures) in many cases. MR cholangiography has been shown to be more accurate than CT or ultrasound in detecting the presence, location and cause of biliary obstruction [8, 9, 10, 11]. In fact, the accuracy of MR cholangiography approaches that of endoscopic retrograde cholangiography (ERC), without the invasiveness, cost, contrast or radiation associated with ERC. Therefore, it may be argued that MR cholangiography should replace invasive ERC for the diagnosis of biliary disease [12]. However, this clinical situation should not be considered acute enough to warrant after-hours specialized biliary imaging. Finally, the potential best emergency use of MR imaging of the abdomen is in patients with suspected bile duct leaks. CT can only show secondary findings of a leak (fluid collections, inflammation), but cannot determine the presence of an active leak, detection of which is usually reserved for contrast cholangiography and hepatobiliary scintigraphy. Several studies have shown that MR is valuable in detecting postoperative biliary complications [13, 14]. Contrast-enhanced MR cholangiography is a new technique being investigated for its utility in demonstrating biliary anatomy and detecting the presence and location of bile duct leaks [15, 16]. This exam is acquired with gradient echo (GRE) images between 1 and 2 h after intravenous administration of mangafodipir trisodium (Teslascan, Amersham Health, Princeton, New Jersey) (K.M. Vitellas et al., presented at the American Roentgen Ray Society, May 2001). Since manganese is a paramagnetic metal ion, it shortens the longitudinal Emergency Radiology (2002) 9: 73–74 DOI 10.1007/s10140-002-0196-9