Patent Foramen Ovale Unmasked: A Contemporary Critical Review of Diagnostic Evaluation and Evidence-based Closure Indications

A patent foramen ovale (PFO) is present in roughly one quarter of adults, yet it becomes clinically consequential in only a small minority. This asymmetry defines the central difficulty of the field: distinguishing a causally implicated interatrial communication from an anatomical variant that happens to have been imaged. Over the past decade, four randomised trials and their pooled analyses have transformed transcatheter closure from a contested intervention into a guideline-supported therapy for selected patients with otherwise cryptogenic ischaemic stroke, while simultaneously exposing how strongly benefit depends on patient selection rather than on the procedure itself. This critical narrative review evaluates the contemporary evidence underpinning diagnostic evaluation and closure indications, and examines the methodological foundations on which current recommendations rest. Literature was identified through structured searching of biomedical and multidisciplinary scholarly sources, supplemented by citation tracking and examination of guideline documents, with critical appraisal directed at study design, comparator choice, outcome ascertainment, and generalisability. Four analytical themes are developed: the mechanistic plurality underlying PFO-associated stroke, which now encompasses paradoxical embolism, in-situ thrombosis within the tunnel, and an atrial arrhythmogenic substrate; the comparative performance and interpretive limits of contrast transthoracic echocardiography, transoesophageal echocardiography, contrast transcranial Doppler and cross-sectional imaging, none of which constitutes a validated reference standard; the migration from crude anatomical criteria to probabilistic causal attribution through the Risk of Paradoxical Embolism score and the PFO-Associated Stroke Causal Likelihood classification; and the calibration of net benefit against device-associated harm, principally atrial fibrillation. Evidence is strongest for closure in patients aged 18 to 60 years with an embolic-appearing infarct, no competing mechanism, and high-risk anatomy. Evidence remains weak or absent for older adults, for thrombophilic patients, for migraine, and for most non-stroke indications. Priority research needs are randomised evaluation in adults older than 60 years with high-risk anatomy, prospective validation of causal attribution instruments in unselected practice, and standardisation of shunt quantification.