Embolism Syndromes
Overview
An embolus is any material (thrombus, fat, gas, amniotic fluid, tumour) that travels via the vascular system to obstruct a vessel at a distant site. Pulmonary Embolism (PE) is the most clinically important, but several other embolic syndromes carry significant mortality.
Pulmonary Embolism (PE)
- Source: Most commonly from deep vein thrombosis (DVT) in the iliofemoral system (proximal DVT = high embolic risk).
- CTPA Findings: Filling defect(s) within the pulmonary arteries (saddle embolus = central; lobar/segmental/subsegmental peripheral). RV:LV ratio >0.9 = RV strain. 'Hampton's hump' = peripheral wedge-shaped infarct. 'Westermark sign' on CXR = oligaemia distal to obstruction.
- V/Q Scan: For patients with renal impairment or contrast allergy. High-probability = >2 segmental mismatches with normal ventilation ('V/Q mismatch').
Fat Embolism Syndrome
Fat emboli are released from fractured long bone medullary fat, producing a triad: Petechial rash, Hypoxia, and Neurological dysfunction appearing 24-72 hours after injury. CXR shows bilateral diffuse alveolar infiltrates ('fluffy infiltrates'). MRI brain shows 'starfield' pattern of DWI restricted cytotoxic lesions.
Amniotic Fluid Embolism (AFE)
AFE occurs when amniotic fluid enters maternal circulation during labour, triggering an anaphylactoid-type immune reaction. Presents with acute cardiorespiratory collapse, DIC, and altered consciousness. Highly fatal (mortality 20-60%). No specific imaging — diagnosis is clinical/post-mortem (fetal squames in maternal pulmonary vasculature).
WarningMassive PE Management
Massive PE = PE with haemodynamic instability (SBP <90 mmHg). CT shows large central filling defects with RV dilatation, interventricular septal bowing leftward ('D-sign'), and RV:LV ratio >1.0. Treatment: systemic thrombolysis (tPA) unless contraindicated. Catheter-directed thrombolysis or surgical embolectomy as alternatives.
High Yield Facts
LightbulbFRCR / MD Prep Pearl
Wells Score stratifies pre-test probability of PE. PERC rule rules out PE in low-probability patients without imaging. For subsegmental PE: evidence favours anticoagulation in patients with DVT or poor cardiorespiratory reserve. Gold standard for DVT = venous duplex ultrasound (non-compressibility of vein = DVT).