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Difficulty: MediumOrdering Imaging Studies

A 68-year-old man presents to the emergency department with acute-onset dyspnea and right-sided pleuritic chest pain that began 2 hours ago. He has a history of hypertension, type 2 diabetes mellitus, and chronic kidney disease. He recently returned from a 12-hour international flight. Vital signs include a blood pressure of 135/85 mm Hg, a heart rate of 112/min, a respiratory rate of 22/min, and an oxygen saturation of 93% on room air. Physical examination reveals clear lungs bilaterally. His right calf is mildly swollen, erythematous, and tender to palpation. Laboratory studies show a serum creatinine level of 2.6 mg/dL (patient's baseline is 2.4 mg/dL). A chest radiograph demonstrates clear lung fields without consolidation, pleural effusion, or pneumothorax. Which of the following is the most appropriate next imaging study to establish the diagnosis?

  1. A
    Computed tomography angiography of the chest
  2. B
    Non-contrast computed tomography of the chest
  3. Ventilation-perfusion (V/Q) scanAnswer
  4. D
    Transthoracic echocardiography
  5. E
    Catheter-directed pulmonary angiography

Answer

The correct answer is a ventilation-perfusion (V/Q) scan.
The correct answer is the ventilation-perfusion (V/Q) scan. This patient has a high clinical probability of a pulmonary embolism (PE) based on his presentation (dyspnea, pleuritic pain, prolonged travel, and signs of concurrent deep vein thrombosis). While computed tomography angiography (CTA) of the chest is generally the first-line imaging modality to definitively diagnose a PE, this patient has significant chronic kidney disease with an elevated serum creatinine level of 2.6 mg/dL. The administration of intravenous iodinated contrast used in CTA can precipitate contrast-induced nephropathy. In patients with suspected PE who have contraindications to CTA, a V/Q scan is the imaging modality of choice, provided their baseline chest radiograph is normal (as abnormalities like pneumonia or large effusions can cause false-positive V/Q mismatch defects).

Step-by-Step Solution

1
Identify the most likely diagnosis based on the clinical presentation.
The patient has a high clinical probability of a pulmonary embolism (PE).
The patient presents with the classic triad of dyspnea, pleuritic chest pain, and signs of deep vein thrombosis (calf swelling and tenderness) following a period of prolonged immobilization (a 12-hour flight).
2
Assess the patient for contraindications to standard initial imaging modalities.
The patient has significant chronic kidney disease with an elevated serum creatinine.
While computed tomography angiography (CTA) of the chest is the typical first-line imaging for suspected PE, the required iodinated contrast carries a high risk of precipitating contrast-induced nephropathy in this patient.
3
Determine the best alternative imaging study.
A ventilation-perfusion (V/Q) scan is selected.
In a hemodynamically stable patient with a contraindication to CTA and a normal baseline chest radiograph, a V/Q scan is highly sensitive and specific for diagnosing a pulmonary embolism without risking kidney injury.

Key Concept

In a hemodynamically stable patient with a high clinical probability of a pulmonary embolism and an absolute or relative contraindication to iodinated contrast (such as severe chronic kidney disease), a ventilation-perfusion (V/Q) scan is the most appropriate diagnostic imaging study, provided the baseline chest radiograph is clear.
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Ordering Imaging Studies

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