Positional PFO shunt explains hypoxaemia in patient with multiterritorial strokes

A case report in Intensive Care Medicine describes multiterritorial ischaemic strokes with unexplained positional hypoxaemia. Brain MRI showed a right anterior cerebral artery infarct and, 24 hours later, a new cerebellar infarct. Transoesophageal echocardiography identified an atrial septal aneurysm and a patent foramen ovale (PFO), with minimal contrast passage supine but more than 20 microbubbles reaching the left atrium within three cardiac cycles when raised.

Supine on oxygen at 5 L/min, PaO2 was 75.8 mmHg and SaO2 96.5%; seated despite 15 L/min oxygen, these fell to 56.3 mmHg and 87%. There was no echocardiographic evidence of pulmonary hypertension. CT excluded pulmonary embolism and pulmonary arteriovenous malformation but showed a 19-cm hepatic cyst compressing and displacing the right-sided cardiac chambers, likely redirecting venous flow towards the PFO.

Cyst drainage yielded 3.5 L and enabled oxygen discontinuation within hours. Hypoxaemia recurred five days later as the cyst reaccumulated; subsequent PFO closure achieved oxygen independence within two hours. The authors recommend supine and raised-position contrast echocardiography for severe, posture-dependent hypoxaemia disproportionate to pulmonary imaging.

This single case supports an anatomical mechanism for substantial right-to-left shunting without pulmonary hypertension. However, paradoxical embolism remained unproven: no venous thrombosis was identified, and seven days of telemetry without atrial fibrillation could not exclude occult paroxysmal atrial fibrillation. The PFO’s causal contribution to the strokes therefore remains uncertain.