Diagnosing pregnant women suspected of appendicitis is tricky business. Often the enlarged uterus will displace the appendix, making it hard to find with ultrasound. Using CT because the physician can't see the appendix on ultrasound raises the issue of fetal radiation exposure. These problems are pushing many physicians to MR.

Acute appendicitis occurs in approximately one in 1500 pregnancies, according to one study, and it is one of the leading indications for surgery in pregnancy (Mil Med 1999;164:671-674). Researchers in another study found that acute appendicitis complicates approximately one in 766 pregnancies (Acta Obstet Gynecol Scand 1999;78:758-762).

The standard of care for pregnant women suspected of appendicitis uses ultrasound first, then MR or CT, according to Dr. Marcia Javitt, section editor for women's imaging at the American Journal of Roentgenology and section head of body MRI at Walter Reed Army Medical Center in Washington, DC.

Dr. Gary Israel, an associate professor of diagnostic radiology and chief of body CT at Yale University, expects physicians eventually to forgo ultrasound and move directly to MR. Others share Israel's opinion. Dr. Ajay Singh, an assistant professor of radiology at Harvard Medical School, calls MRI of the appendix “the next frontier for widespread use,” citing concerns of radiation effects.

“When ultrasound findings are nondiagnostic or equivocal, MR imaging is the most appropriate modality for the evaluation of acute appendicitis in pregnant women,” Singh wrote in a study published in RadioGraphics (2007;27[5]:1419-1431).

“Although the high cost and restricted availability of MR imaging limit its utility in the emergency setting, the absence of ionizing radiation and the improved contrast resolution make MR imaging an appropriate modality for use in selected patients.”

Several studies suggest MR may be the best option when it comes to diagnosing pregnant women suspected of appendicitis.

Dr. Lodewijk P. Cobben from the radiology department at Medisch Centrum in Haaglanden, the Netherlands, and colleagues conclude in their 12-patient study that MRI is a valuable and safe technique for the evaluation of pregnant patients clinically suspected of having acute appendicitis (AJR 2004;183:671-675).

A study by Dr. Ivan Pedrosa, director of body MRI at Beth Israel Deaconess Medical Center in Boston, and colleagues evaluated 51 pregnant women suspected of acute appendicitis using MRI (RadioGraphics 2007;27:721-753). Four patients had findings suspicious for appendicitis, and three were inconclusive. Overall sensitivity was 100%, and specificity was 93.6%.