RD7.3 | Imaging in Pulmonary Embolism — Summary & Reflection

KEY TAKEAWAYS

Imaging in Pulmonary Embolism — Key Points

• Imaging is the endpoint of a structured pathway: estimate pre-test probability (Wells / revised Geneva), then use D-dimer in 'unlikely' patients (age-adjusted cut-off = age × 10 ng/mL over age 50), then definitive imaging only when indicated.
• D-dimer is sensitive but not specific — a normal value excludes PE in low-probability patients; a raised value never confirms it.
• CT pulmonary angiography (CTPA) is the first-line modality of choice (fast, available, ~83% sensitivity/~96% specificity in PIOPED II, and reveals alternative diagnoses). The diagnostic sign is an intraluminal filling defect (polo-mint / railway-track signs; saddle embolus when central).
• V/Q scintigraphy is the principal alternative when CTPA is contraindicated — chiefly iodinated contrast allergy and renal impairment (eGFR <30) — and performs best with a normal chest radiograph; the hallmark is a mismatched (ventilated, non-perfused) defect.
• Pregnancy: consider leg compression ultrasound first; if chest imaging is needed with a normal CXR, a perfusion-only (Q) scan gives a lower breast dose; CTPA is also acceptable.
• Chest radiograph is usually normal in PE; its role is to find alternative diagnoses. Classic (insensitive) signs: Westermark (oligaemia), Hampton's hump (infarct), Fleischner (enlarged PA).
• Right-ventricular strain matters: RV/LV ratio >1.0 on CTPA, septal bowing and echocardiographic RV dilatation/McConnell sign identify higher-risk patients.
• Management is risk-stratified: stable PE → anticoagulation (DOAC/LMWH); high-risk (massive) PE with shock and RV strain → systemic thrombolysis (or catheter-directed/surgical reperfusion); normotensive patients are stratified by sPESI, troponin and RV/LV ratio; a negative scan safely excludes PE.

REFLECT

When you are next on the medical admissions unit and a breathless patient is being assessed, consciously trace the diagnostic chain: Was a pre-test probability score calculated, or was the decision to scan (or not scan) made on a hunch? Was a D-dimer used appropriately, and was the age-adjusted cut-off applied? If a CTPA was ordered, ask whether the patient's renal function and contrast history were checked first, and what the alternative would have been. When the result comes back, notice whether the team integrated the right-ventricular findings into the treatment decision or simply 'started anticoagulation'. Making this chain explicit — probability, modality, findings, management — is how the abstract competency becomes reliable clinical judgement.