Abstract Body (Do not enter title and authors here): Background
Purulent pericarditis is a very rare manifestation of infective endocarditis (IE) with a high mortality rate, particularly in the setting of Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. Even more perplexing is the rapid progression to hemodynamically significant cardiac tamponade in the context of early negative echocardiographic studies. This case demonstrates a unique presentation of MRSA endocarditis with an initial negative echocardiogram complicated by purulent pericarditis and pericardial tamponade.

Case Presentation
A 44-year-old woman with a history of intravenous drug use presented with altered mentation and multifocal intracranial hemorrhages. Imaging demonstrated cavitating lung lesions, wedge-shaped areas of decreased perfusion within the bilateral kidneys, raising suspicion for septic emboli. Serial blood cultures were positive for MRSA. Despite ongoing fevers, leukocytosis, and persistent bacteremia, both initial transthoracic and transesophageal echocardiograms (TTE/TEE) did not demonstrate vegetations or significant pericardial effusion.

Due to persistent bacteremia and worsening hemodynamics, a repeat TEE was performed, which revealed a new, large circumferential pericardial effusion with right atrial systolic collapse, right ventricular diastolic collapse, plethoric IVC, a 1.4 × 0.8 cm highly mobile vegetation on the mitral valve subvalvular apparatus, and multiple large echogenic structures in the pericardial space concerning for vegetation. Pericardiocentesis revealed a purulent, MRSA-positive fluid, confirming purulent pericarditis. The antibiotics regimen was intensified and the patient was transferred to a higher level of care facility for cardiac surgery evaluation.

Conclusion
This case underscores the importance of maintaining a high index of suspicion for infective endocarditis in patients presenting with atypical symptoms, particularly in those with a history of intravenous drug use and persistent MRSA bacteremia. Clinicians must remain vigilant for evolving cardiac pathology despite initially reassuring imaging results. The integration of clinical judgment and advanced imaging techniques is essential for optimizing patient outcomes in such challenging scenarios.