When the Brainstem Is the Target: Cryptogenic Paramedian Pontine Infarction Associated With Patent Foramen Ovale

A 46-year-old woman without traditional vascular risk factors presented with one week of persistent vertigo and a nonfocal neurologic examination. Brain MRI revealed an acute to early subacute infarct in the left paramedian pons. CT angiography of the head and neck demonstrated no large-vessel disease, and a thrombophilia panel was unremarkable. Further evaluation identified a patent foramen ovale (PFO) with an atrial septal aneurysm and septal bowing, with a large right-to-left shunt on transthoracic echocardiography and a moderate shunt on transesophageal echocardiography bubble study. She had a Risk of Paradoxical Embolism (RoPE) score of 7 and met PFO-Associated Stroke Causal Likelihood (PASCAL) "Probable" criteria. Isolated paramedian pontine infarction is classically attributed to branch atheromatous disease, but the absence of small-vessel disease markers, the posterior circulation lesion location, and high-risk PFO anatomy together favored a paradoxical embolic mechanism. She received dual antiplatelet therapy followed by aspirin monotherapy, with referral for percutaneous PFO closure. This case illustrates how RoPE and PASCAL can help estimate whether a detected PFO is likely pathogenic rather than incidental in a perforator-territory stroke, and underscores that persistent vertigo without focal deficits warrants timely stroke imaging.