The Heart-Brain Bypass: Paradoxical Septic Embolism Through a Patent Foramen Ovale (PFO)

Brain abscesses are rare sequelae of paradoxical septic embolism from cardiac sources, particularly in the absence of valvular endocarditis. Diagnosis remains challenging, and a high index of clinical suspicion is often required. We present a 65-year-old female with a past medical history of hypertension and dyslipidemia with a chief complaint of altered mental status. She was found to have left-sided focal seizures and dysarthria. Computed tomography (CT) of the head with and without contrast, with subsequent confirmatory magnetic resonance imaging (MRI) of the head with contrast, revealed a 3.5 cm ring-enhancing lesion in the right frontal lobe, consistent with a brain abscess. Craniotomy and drainage yielded <i>Streptococcus intermedius</i>, suggesting a likely dental source. A transesophageal echocardiogram (TEE) identified a large multilobular right atrial mass and an interatrial shunt, likely a patent foramen ovale (PFO), enabling paradoxical embolization. AngioVac (AngioDynamics, Latham, NY, USA) aspiration of the right atrial mass, targeted antibiotic therapy, and guideline-directed medical therapy (GDMT) provided a multimodal treatment plan to best suit the patient's individual needs. This case illustrates the importance of considering atypical sources in brain abscesses of unclear origin. The necroinflammatory infiltrate found on pathology of the right atrial mass, in addition to abscess cultures demonstrating heavy growth of <i>S. intermedius</i>, suggests that the right atrial mass served as a nidus for septic embolization to the brain through the patient's PFO. Due to a critical illness on initial presentation, the patient was started on empiric antibiotics on admission. Blood cultures and cultures of the right atrial mass were subsequently negative for any organisms. It was noted by clinical history that the patient had invasive dental work approximately two weeks prior to presentation. Given the above information, the most likely cause of the patient's brain abscess was culture-negative nonvalvular bacterial endocarditis. In the absence of a mechanical valve and intravenous drug use, turbulent flow induced endothelial injury, likely exposing fibrin on the lateral wall of the right atrium. The patient was ultimately discharged with close outpatient follow-up with marked improvement in symptoms. Early recognition, advanced imaging, and multidisciplinary management, including neurosurgical intervention, cardiothoracic surgery, and infectious disease consultation, were critical for optimizing outcomes.