Imaging the acute abdomen in pregnancy: a radiological decision-making tool and the role of MRI

Acute abdominal pain in pregnancy poses a significant diagnostic challenge. The differential diagnosis is wide, clinical assessment is difficult, and the use of conventional imaging methods is restricted due to risks to the fetus. This can lead to delay in diagnosis, which increases the risk of maternal and fetal harm. Imaging techniques not involving ionising radiation are preferred. Sonography remains first line, but anatomical visualisation can be limited due to displacement of adjacent structures by the gravid uterus. MRI provides excellent cross-sectional soft-tissue assessment of the abdomen and pelvis, and no study to date has demonstrated significant deleterious effects to the fetus at any gestation; however, there remains a theoretical risk of tissue heating by radiofrequency pulses, and there must be consideration of benefit versus potential risk for any use of magnetic resonance imaging (MRI) in pregnancy. With a limited protocol of sequences, a broad spectrum of pathologies can be evaluated. Computed tomography carries the highest exposure of ionising radiation to the fetus, but may be necessary, particularly in cases of trauma. The patient must be kept informed and any potential risks to the patient and fetus should be clearly explained. We present a radiological decision-making tool to guide choice of imaging and best establish the underlying diagnosis in the acute pregnant abdomen. In addition, using illustrative examples from our practice at a large tertiary centre, we review the advantages and disadvantages of each imaging method, with particular focus on the utility of MRI.