Would a pulmonary embolism (PE) show on a chest X-ray?

Chest X-Ray for Pulmonary Embolism Detection

A chest X-ray is rarely diagnostic for pulmonary embolism and cannot reliably detect or exclude PE, but it remains valuable for identifying alternative diagnoses that mimic PE and for guiding interpretation of ventilation-perfusion scans. 1

Diagnostic Limitations of Chest X-Ray

The chest radiograph is abnormal in 88% of patients with confirmed PE, making a normal chest X-ray uncommon but not exclusionary 2. However, the findings lack specificity:

• Atelectasis or infiltrate appears in 49% of PE cases but also in 45% of non-PE cases, making it a poor discriminator 3, 1
• Pleural effusion occurs in 46% of PE cases versus 33% in non-PE cases 3, 1
• Elevated diaphragm is present in 36% of PE cases and 25% of non-PE cases 3, 1

Specific Radiographic Signs and Their Limited Value

While certain findings are more suggestive of PE, they remain insufficiently sensitive or specific for diagnosis:

• Hampton's hump (pleural-based wedge-shaped opacity representing pulmonary infarction) appears in only 23% of PE cases 3, 1
• Westermark sign (decreased pulmonary vascularity) is found in 36% of PE cases but also in 6% of non-PE cases 3, 1
• Amputation of hilar artery occurs in 36% of PE cases but is more specific, appearing in only 1% of non-PE cases 3, 1

The PIOPED study definitively demonstrated that these classic radiographic findings are poor predictors of PE and cannot be used to confirm or exclude the diagnosis 2.

Primary Clinical Utility

The main value of chest X-ray is to exclude alternative diagnoses that clinically mimic PE, including 1, 2:

• Pneumonia
• Pneumothorax
• Heart failure
• Myocardial infarction
• Pericarditis
• Lobar collapse
• Tumor

Additionally, chest X-ray findings are essential for interpreting ventilation-perfusion scans, as radiographic abnormalities affect V/Q scan interpretation 3.

Definitive Diagnostic Approach

CT pulmonary angiography (CTPA) is now the primary imaging modality for evaluating suspected PE and should be performed when clinical suspicion warrants imaging 3, 1. The diagnostic algorithm should proceed as follows:

1. Assess clinical probability using validated scores (Wells, Geneva) or clinical gestalt 4

2. D-dimer testing in patients with low or intermediate probability:

   • D-dimer <500 ng/mL excludes PE with post-test probability <1.85% 4
   • Skip D-dimer in high-probability patients and proceed directly to CTPA 4

3. CTPA for definitive diagnosis when indicated by clinical probability and D-dimer results 3, 1

4. V/Q scanning as an alternative when CTPA is contraindicated (pregnancy, severe renal failure, contrast allergy) 3

Critical Clinical Pitfall

Do not rely on chest X-ray to diagnose or exclude PE—additional imaging with CTPA or V/Q scan is always required when PE remains in the differential diagnosis 1, 2. Recent evidence demonstrates that chest X-ray provides minimal incremental diagnostic value to validated clinical algorithms like YEARS, and routine CXR prior to CTPA is not necessary in all patients with suspected PE 5.

A normal chest X-ray in a patient with acute dyspnea, hypoxemia, and risk factors should increase rather than decrease clinical suspicion for PE 1.