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Just MoRe Imaging?
MRI Evaluation of Acute Abdominal Pain
David A. Boyajian, MD
Dr Boyajian is clinical director of radiology at New York-Presbyterian/Lower Manhattan Hospital, and vice chairman and assistant professor of radiology, Department of Radiology, Weill Cornell Medical College, New York.
For the past few decades, the established cross-sectional imaging modalities used to evaluate acute abdominal pain in the ED have been computed tomography (CT) and ultrasound. Advantages of these modalities include the widespread availability of equipment and qualified technologists and radiologists, the ability to obtain images quickly, and relative cost-effectiveness. There are, however, several subsets of indications for which traditional cross-sectional imaging approaches are either undesirable or have a low sensitivity for accuracy (eg, suspected nonobstetric pathology in the pregnant patient, biliary ductal pathology).
Magnetic resonance imaging (MRI) has become more widely available to ED practices across the country and an increasingly important tool in the arsenal of the emergency radiologist. Advantages of MRI include better soft-tissue characterization, ability to directly image in any plane, and the lack of ionizing radiation.
There are, however, barriers to using MRI in the emergency setting, including availability and location of the MRI scanners, long examination time, difficulty in monitoring unstable patients, and higher cost.1 In addition, relative to CT and ultrasound, there is poorer spatial resolution and greater potential for artifacts. Advances in MRI technology and workflow, including rapidly acquired imaging sequences and active radiologist management of such cases, can significantly reduce examination acquisition time and improve image quality. Due to the significant advantages in visualizing the brain and spine, MRI has become the gold standard in many emergent conditions such as suspected stroke and spinal cord compression. Increasingly, MRI is being used to diagnosis causes of abdominal pain, examples of such are discussed below.
Appendicitis in Pregnancy
Although acute appendicitis is the most common nonobstetric surgical condition during pregnancy, several factors such as physiological leukocytosis and appendiceal displacement (which reduces the sensitivity of ultrasound) confound the diagnosis. Due to the radiation conveyed by CT, MRI is considered a more appropriate imaging modality in this patient population.2 In a retrospective study of 23,290 pregnant patients, Pedrosa et al3 reported a sensitivity of 100%, specificity of 93.6%, and accuracy of 94% in detecting acute appendicitis in patients for whom ultrasound was inconclusive.
Biliary Pathology
Biliary pathology, particularly choledocholithiasis, may not be demonstrated to advantage with cross-sectional imaging. For example, CT sensitivity for detection is decreased in the absence of ductal dilatation and/or in poorly mineralized stones. Technical factors, such as obesity, patient positioning, and bowel gas, limit evaluation with ultrasound. MRI is able to depict both the intrahepatic and extrahepatic biliary ducts and identify any intraductal lesions (eg, masses, stones). Special MRI contrast agents that are excreted through the bile ducts have come to market in recent years and can assist in evaluation for biliary pathology. The sequences have replaced many of the diagnostic endoscopic retrograde cholangiopancreatograms (ERCP) that used to be performed. An advantage of magnetic resonance cholangiopancreatography (MRCP) is that structures outside of the biliary system may also be evaluated (eg, liver, kidneys).