American Board of Internal Medicine (ABIM) Certification Practice Exam

If the ultrasound is normal in a pregnant patient suspected of having a pulmonary embolism, which is the next diagnostic modality?

1. CT pulmonary angiography

2. Magnetic resonance imaging (MRI)

3. Ventilation-perfusion (V/Q) lung scan

4. Lower extremity venous duplex ultrasonography

The correct answer is: Ventilation-perfusion (V/Q) lung scan

In a pregnant patient suspected of having a pulmonary embolism (PE) with a normal ultrasound, the next appropriate diagnostic modality is a ventilation-perfusion (V/Q) lung scan. This imaging technique is particularly useful because it assesses the blood flow and air flow in the lungs, helping to identify any mismatches that suggest the presence of a PE. V/Q scanning is favored in pregnancy due to its lower risk of radiation exposure to the fetus compared to other imaging modalities like CT pulmonary angiography. Although CT pulmonary angiography is a sensitive and specific test for PE, the concern regarding radiation exposure to the developing fetus makes it a less favorable first-line choice in pregnant patients. MRI, while it does not involve ionizing radiation, is not typically used to diagnose PE as its availability and the specific protocols required (e.g., using MR angiography) limit its practicality in acute settings for this diagnosis. Lower extremity venous duplex ultrasonography is useful in cases where a deep vein thrombosis (DVT) is suspected, serving as a proximal source for the PE, but a normal ultrasound indicates that there is no DVT, thus making it an inappropriate next step in confirming or ruling out a PE. Therefore, the V/Q lung