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Difficulty: Very hardOrdering Imaging Studies

Presenting to the emergency department is a 29-year-old pregnant patient at 27 weeks of gestation, complaining of acute-onset dyspnea and sharp, left-sided chest pain exacerbated by deep breathing. Her current pregnancy has been unremarkable, and she takes only prenatal vitamins. On arrival, her temperature is 37.2°C (99.0°F), blood pressure is 114/74 mm Hg, heart rate is 118/min, and respiratory rate is 24/min. Pulse oximetry indicates an oxygen saturation of 94% on room air. The patient appears acutely anxious. Auscultation of the lungs reveals diminished breath sounds at the left base. Cardiac auscultation shows tachycardia but no murmurs, rubs, or gallops. Examination of the lower extremities reveals no edema, erythema, or tenderness. An electrocardiogram shows sinus tachycardia. Bilateral lower extremity compression venous ultrasonography is negative for deep vein thrombosis. A portable chest radiograph demonstrates a small left-sided pleural effusion and atelectasis in the left lower lobe. Which of the following is the most appropriate next step in diagnostic imaging for this patient?

  1. A
    Ventilation-perfusion (V/Q) scan
  2. B
    Noncontrast computed tomography of the chest
  3. Computed tomography of the chest with intravenous contrastAnswer
  4. D
    Contrast-enhanced magnetic resonance imaging of the chest
  5. E
    Transthoracic echocardiography

Answer

The correct answer is computed tomography of the chest with intravenous contrast.
The patient's clinical presentation of acute dyspnea, pleuritic chest pain, and tachycardia in the setting of pregnancy is highly suspicious for a pulmonary embolism (PE). Pregnancy induces a hypercoagulable state, significantly increasing the risk of venous thromboembolism. The diagnostic algorithm for suspected PE in pregnancy begins with bilateral lower extremity compression ultrasonography, as finding a deep vein thrombosis (DVT) would warrant therapeutic anticoagulation without the need for further fetal or maternal radiation exposure. If the ultrasound is negative, the next required step is a chest radiograph. The choice of subsequent definitive imaging depends heavily on the radiograph results. If the chest radiograph is completely normal, a ventilation-perfusion (V/Q) scan is preferred because it delivers a lower radiation dose to maternal breast tissue compared to CT imaging. However, if the chest radiograph is abnormal (e.g., showing a pleural effusion, infiltrate, or atelectasis, as seen in this patient), a V/Q scan is highly likely to yield an indeterminate (non-diagnostic) result. In such cases, computed tomography of the chest with intravenous contrast (CT pulmonary angiography) is the most appropriate next step to definitively diagnose or exclude a PE.

Step-by-Step Solution

1
Evaluate the patient's clinical presentation and initial test results.
The patient is a pregnant woman with acute pleuritic chest pain, dyspnea, and tachycardia, which creates a high clinical suspicion for pulmonary embolism (PE). Her initial lower extremity ultrasound is negative for deep vein thrombosis.
Establishing the pre-test probability and reviewing prior diagnostics dictates the specific evidence-based algorithm for PE workup in pregnancy.
2
Analyze the chest radiograph findings in the context of the diagnostic algorithm.
The chest radiograph is abnormal, demonstrating a left-sided pleural effusion and atelectasis.
The chest X-ray result is the key decision point determining whether a V/Q scan or a contrast-enhanced CT is the appropriate next definitive imaging modality.
3
Select the most appropriate definitive imaging study based on the abnormal radiograph.
Computed tomography of the chest with intravenous contrast is selected as the next step.
An abnormal chest X-ray renders a V/Q scan likely indeterminate. Contrast-enhanced CT definitively images the pulmonary vasculature and avoids the delay associated with non-diagnostic testing.

Key Concept

In pregnant patients with suspected pulmonary embolism and a negative lower extremity ultrasound, an abnormal chest radiograph dictates that computed tomography of the chest with intravenous contrast is the preferred next imaging step, as a V/Q scan would likely be indeterminate.
Estimated Time:1m 30s
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Ordering Imaging Studies

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