Question 2 of 6

Question 2

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Proposed mechanism

The sequence — a minor blunt-trauma impact to the lower limb, followed by a period of immobility (the flight), followed days later by sudden dyspnoea and collapse — is the classic presentation of a deep vein thrombosis (DVT) that embolised to the pulmonary circulation. Virchow’s triad explains why the seemingly trivial impact is causally relevant: (1) endothelial injury to a lower-limb vein from the gentle collision provides a nidus for platelet adhesion and clot initiation; (2) venous stasis during the subsequent flight (prolonged immobile sitting, dependent legs, cabin hypobaric/dehydrating conditions) allows a thrombus to propagate in the calf/popliteal veins without being washed out by the calf-muscle pump; (3) a degree of hypercoagulability (the stress response to trauma and travel raises clotting factors and lowers fibrinolytic activity) further favours clot growth. Over the following days the thrombus enlarges and eventually a fragment (or the whole clot) detaches, travels through the right heart, and lodges in the pulmonary arterial tree as a pulmonary embolus (PE). A large saddle-embolus (straddling the main pulmonary artery bifurcation) or a large single-vessel occlusion acutely obstructs right ventricular outflow, causes acute right heart strain and hypoxaemia, and can produce sudden collapse and death from acute cor pulmonale/electromechanical dissociation — exactly the picture described.

Expected autopsy findings

• A residual thrombus (often with lines of Zahn, showing it formed before death, in flowing blood) in a deep vein of the lower leg — the embolic source.
• An occlusive thromboembolus lodged in the pulmonary artery or its major branches (a saddle embolus at the bifurcation is the classic sudden-death finding); the embolus's laminated, lines-of-Zahn appearance and its physical fit to the vessel confirm it embolised rather than formed in situ.
• Acute right ventricular dilatation and strain (thin-walled RV distension), reflecting the sudden afterload imposed on the right heart by the obstruction.
• If death was not immediate, a haemorrhagic, wedge-shaped pulmonary infarct in the lung periphery downstream of a smaller occluded branch, with pleural surface fibrin/haemorrhage.
• Systemic findings of hypoxic/shock death (petechial haemorrhages, congested viscera) if the terminal event was more protracted than an instantaneous large PE.