Pontine Infarction Presenting With Right Internuclear Ophthalmoplegia in a Patient With Patent Foramen Ovale and May-Thurner Syndrome: A Case Report.

Patent foramen ovale (PFO) is a common congenital cardiac anomaly associated with cryptogenic ischemic stroke in adults. The likelihood of PFO-associated stroke is increased in the presence of high-risk anatomical features such as substantial right-to-left shunting or an associated atrial septal aneurysm (ASA). Brainstem ischemic events associated with PFO, however, are less frequently reported. We present the case of a 59-year-old man who developed dizziness, binocular diplopia, right internuclear ophthalmoplegia (INO), and gait instability. Magnetic resonance imaging demonstrated an old pontine infarct without evidence of recent or acute infarction; however, based on the acute clinical presentation and neurologic examination, neurology considered the presentation clinically consistent with a subacute pontine ischemic infarct. Subsequent cardiac evaluation demonstrated a PFO with right-to-left shunting and an associated ASA, and the patient later underwent successful percutaneous PFO closure. The coexistence of May-Thurner syndrome (MTS) provided a potential venous thrombotic substrate for paradoxical embolism, although no active venous thrombus was documented. This case highlights an uncommon brainstem presentation in a patient with high-risk PFO anatomy and emphasizes the importance of distinguishing a plausible paradoxical embolic mechanism from proven causation.