Case Presentation: A 36-year-old male with a medical history significant for IV heroin abuse and bipolar disorder presented to the hospital with confusion, fever and chills. Initial vitals were concerning for septic shock, and the patient was promptly started on broad-spectrum antibiotics and aggressively fluid resuscitated following sepsis protocols. Physical examination was concerning for a general toxic appearance, left knee effusion, cervical spine tenderness, and diffuse pulmonary rhonchi. Blood cultures were drawn and MRSA was isolated within 24 hours. The patient was unable to provide a reliable history secondary to his mental status, but family members note that he is an active IV drug user. Work-up revealed multiple cavitary pulmonary lesions concerning for septic emboli, cervical osteomyelitis, and left knee septic arthritis. A transesophageal echocardiogram (TEE) was obtained to evaluate for endocarditis. This revealed a 4.6 cm x 3 cm mobile, heterogeneous mass in the right atrial appendage without valvular involvement. The patient remained bacteremic for 8 days despite appropriate antibiotics, necessitating surgical intervention for source control, which was suspected to be the intracardiac mass. Given the overall clinical situation as well as the TEE findings, the patient was placed on cardiopulmonary bypass and a sternotomy with right atriotomy was performed. This revealed a large, multilobulated, densely adherent mass in the right atrial appendage which required the excision of a significant amount of atrial wall tissue and aggressive debridement. The appearance was not consistent with an atrial tumor. The postoperative course was complicated by respiratory failure requiring ECMO and prolonged intubation. This was determined to be secondary to an overwhelming inflammatory response from intraoperative manipulation of the infected atrial mass. The patient subsequently made a full recovery and was discharged 3 weeks later in good health.

Discussion: Valvular vegetations in the setting of bacteremia is a common clinical situation, with Staphylococcus aureus being the most commonly isolated bacteria affecting healthy, native valves. Given the turbulent nature of cardiac valvular hemodynamics, valves tend to be the primary sites of infective endocarditis. Free wall and atrial appendage vegetations are quite rare and frequently mimic an atrial thrombus or tumor. This case describes a giant right atrial appendage vegetation, without valvular involvement, in the setting of MRSA bacteremia.

Conclusions: Intra-cardiac vegetations pose a unique diagnostic challenge, even in the setting of bacteremia. They may mimic tumors or thrombi if sufficiently large, and surgical intervention is often required to make a definitive diagnosis in these cases. Although the advent of high-resolution cardiac MRI is increasing our ability to characterize these masses non-operatively, its utility remains adjunctive. Transesophageal echocardiography remains the diagnostic gold standard for cardiac mass evaluation. The case described is unusual based on the location and size of the vegetation, as well as the severe intraoperative inflammatory response.