An 82‐year‐old woman presented to hospital with worsening chronic dyspnoea without fever or other specific symptoms. Despite receiving 100% oxygen via non‐invasive ventilation, arterial oxygen saturation remained low at 70–80%. However, the oxygen saturation improved when positioned flat — a phenomenon known as platypnoea–orthodeoxia, which is associated with right‐to‐left shunts.1,2 Chest x‐ray revealed a left mid‐zone mass contiguous with the hilar vessels (Figure, A, arrow), and echocardiography excluded an intracardiac shunt. Computed tomography scan with intravenous contrast demonstrated a massive pulmonary arteriovenous malformation at the level of the pulmonary arteries (Figure, B [axial] and C [coronal], arrows). This was subsequently managed by radiological embolisation with a 20 mm type II Amplatzer plug (St Jude Medical; Figure, D), with good radiographic result and rapid improvement in arterial oxygenation.3 Pulmonary arteriovenous malformations are an important and reversible cause of hypoxaemia due to right‐to‐left shunting and can result in paradoxical embolic stroke if untreated.4
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