To describe a case of recurrent embolic ischemic strokes in a patient where atrial septal aneurysm (ASA) was the likely cause.

Atrial septal aneurysm (ASA) is underrecognized potential cardioembolic source of ischemic stroke. While patent foramen ovale (PFO) and atrial arrythmias are well-established cardioembolic etiologies, isolated ASA without PFO or arrhythmias remains a diagnostic and therapeutic challenge.

A 66-year-old woman with history of four embolic-appearing ischemic strokes over one year, including left M1 occlusion treated with thrombolysis and thrombectomy involving multiple bilateral cortical, subcortical, and cerebellar territories, presented with new-onset slurred speech. Brain MRI demonstrated an additional acute infarct. Extensive prior evaluations, including cerebral angiography for large-artery disease, prolonged cardiac rhythm monitoring, cerebrospinal fluid studies for vasculitis, and comprehensive hypercoagulable testing, were unremarkable. A prior transesophageal echocardiogram (TEE) had shown a mobile interatrial septum not meeting criteria for aneurysm. She had received 21-day courses of dual antiplatelet therapy after each cerebrovascular event. During this admission, CT imaging of the abdomen revealed new splenic hypodensities, suggestive of systemic emboli, prompting repeat TEE 9 months after the first one, which demonstrated a hypermobile interatrial septum with aneurysmal dilation measuring 12 mm, without intracardiac thrombus or right-to-left shunt. Anticoagulation with apixaban 5 mg twice daily was initiated for indefinite duration. Over six months of follow-up, she remained free of recurrent cerebrovascular events. Residual deficits include mild cognitive impairment consistent with vascular dementia, reflected by a Montreal Cognitive Assessment score of 18/30 with language and executive dysfunction, precluding return to work.

This case highlights atrial septal aneurysm as an underrecognized yet independent source of cardioembolism in the absence of PFO or arrhythmia. According to expert consensus from the 2021 stroke guidelines, indefinite anticoagulation should be considered in such patients with recurrent embolic events to reduce future stroke risk.