Will a CT (Computed Tomography) chest show a pulmonary embolism?

CT Chest for Pulmonary Embolism Detection

A standard CT chest will not reliably show pulmonary embolism - a dedicated CT Pulmonary Angiography (CTPA) is required for accurate diagnosis of PE. 1, 2

Differences Between Standard CT Chest and CTPA

Standard CT Chest with Contrast

• Not optimized for pulmonary artery visualization
• Contrast timing may not coincide with pulmonary arterial phase
• May miss smaller emboli, particularly at subsegmental level
• Not recommended as first-line test for suspected PE

CTPA (Dedicated Protocol)

• Specifically designed with thin-section acquisition
• Precisely timed contrast administration to coincide with peak pulmonary arterial enhancement
• Includes specialized reconstructions and reformats
• Highly sensitive (74-81%) and specific (89-91%) for central and segmental pulmonary emboli 1, 3
• First-line diagnostic imaging tool for suspected PE 1, 2

Diagnostic Algorithm for Suspected PE

1. Clinical Probability Assessment:

   • Use validated clinical prediction rules (Wells score, Geneva score)
   • Categorize patients as PE likely or unlikely

2. D-dimer Testing:

   • For patients with low/intermediate clinical probability
   • If negative in low probability patients, safely excludes PE without imaging 1
   • If positive, proceed to imaging

3. Imaging Selection:

   • CTPA: First-line imaging test for suspected PE 1, 2
   • V/Q scan: Alternative when CTPA is contraindicated
   • Lower extremity ultrasound: For patients with symptoms of DVT

Clinical Pitfalls to Avoid

• Relying on standard CT chest: A routine CT chest with contrast may detect large central emboli but will miss smaller, peripheral emboli 2
• Skipping D-dimer testing: In low probability patients, D-dimer testing can safely exclude PE in approximately one-third of patients, avoiding unnecessary radiation exposure 1, 4
• Overlooking alternative diagnoses: CTPA may reveal alternative diagnoses in approximately 35% of patients without PE, including pneumonia (7%), emphysema (7.6%), atelectasis (5.5%), and heart failure (3.3%) 4

Additional Benefits of CTPA

• Allows assessment of right ventricular dilatation (RVD), which has prognostic significance 5
• High sensitivity (92%) for detecting right ventricular dysfunction 4
• May demonstrate alternative pathology causing symptoms 1
• Fewer "nondiagnostic" studies compared to V/Q scans 1

In summary, while a standard CT chest with contrast may incidentally detect pulmonary embolism, it is not the appropriate test for this specific diagnosis. For patients with suspected PE, a dedicated CTPA protocol is required for accurate diagnosis and should be ordered following appropriate clinical probability assessment and D-dimer testing when indicated.