Native-Valve Staphylococcus epidermidis Endocarditis Complicated by Destructive Pseudoaneurysm of the Mitral-Aortic Intervalvular Fibrosa: A Case Report and Review of the Literature

Background Pseudoaneurysm of the mitral-aortic intervalvular fibrosa (MAIVF) represents a rare but severe complication of infective endocarditis, classically associated with highly virulent organisms such as Staphylococcus aureus. Staphylococcus epidermidis, a coagulase-negative staphylococcus traditionally considered a low-virulence commensal, is increasingly recognized as a cause of clinically significant native-valve endocarditis. Case Summary We report a 72-year-old man with native bicuspid aortic valve who presented with syncope and was found to have S. epidermidis bacteremia. Transthoracic echocardiography demonstrated an aortic valve mass, but transesophageal echocardiography revealed extensive periannular destruction including MAIVF pseudoaneurysm, posterior aortic annular abscess, and a large mitral valve vegetation with associated thrombus. Neuroimaging confirmed multiple embolic cerebral infarcts. Despite aggressive medical therapy, the patient's clinical trajectory precluded surgical intervention, and he ultimately transitioned to comfort-focused care. Conclusion To our knowledge, this represents one of the first reported cases of native-valve S. epidermidis endocarditis complicated by destructive MAIVF involvement in the absence of prosthetic material. This case underscores the underappreciated pathogenic potential of coagulase-negative staphylococci and highlights the critical role of transesophageal echocardiography in detecting periannular complications that may be missed on transthoracic imaging.