Robert Aaron Yost MD, Presenter: Nothing to Disclose

David Maitland Hough MD, Abstract Co-Author: Nothing to Disclose

Magnetic Resonance (MR) imaging is an accepted adjunct to Ultrasonography (US) in evaluation of acute appendicitis (AA) in pregnant patients.  Most MR protocols advocate an oral preparation of Gastromark and barium sulfate, typically administered 60-90 minutes prior to the study.  Iron oxide particles provide negative contrast, and susceptibility effects on T2*-weighted images in the appendix imply lumen patency and allow exclusion of appendicitis (Pedrosa et al. Radiographics 27 (3):721). These exams are often performed off hours, and logistics of administering the oral agent and delay in exam performance is problematic.  However, many investigators find oral agents to be an essential component of the exam.  The purpose of this retrospective review is to examine our data, which does not  include oral contrast agents.

The data of 40 consecutive pregnant women who underwent MR examination for suspected appendicitis from September 2006 through November 2008 were retrospectively reviewed after obtaining institutional review board-approval.  Age of the patient, gestational age, US findings, MR findings, number of pregnancies, and white blood cell (WBC) count were recorded.

The MR exam was interpreted as positive in 6 of 40 cases (15%).  The appendix was not visualized in 9 of 40 (22.5%) of cases.  One of these cases was positive at laparotomy.  The other 8 cases either did not undergo laparotomy or were negative at surgical exploration.   There was 1 false positive and 1 false negative case.  Sensitivity was 5/6=83.3%, specificity 33/34=97.1%, positive predictive value (PPV) 5/6=83.3%, negative predictive value (NPV) 33/34=97.1%.

Recent work reported visualization of a normal appendix in patients without AA in 87% of MR examinations (Pedrosa et. al. Radiology 250 (3): 749). Without the use of oral contrast, the normal appendix was identified in 26/34 (76%) of our cases without AA.  Despite reduced visualization of the appendix without a negative oral contrast, results from our small series suggest adequate performance without waiting for an oral preparation. Ultimately, oral contrast may be reserved for inconclusive cases and be left to the radiologists' discretion.

While improving visualization of the normal appendix, the oral preparation delays the MR exam, can be logistically challenging when performed off hours, and may not increase technique performance.

Yost, R, Hough, D, Effectiveness of MRI in Excluding Appendicitis in Pregnant Women with Right Lower Quadrant Pain without Oral Contrast Agents.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8005236.html