Echocardiographically occult nonbacterial thrombotic endocarditis with tumor cell-containing valvular vegetations in...

Nonbacterial thrombotic endocarditis (NBTE) is an uncommon but important cause of systemic arterial embolism, most often occurring in advanced malignancy. Diagnosis is frequently difficult because vegetations may be small, transient, or not visualized on echocardiography, which may delay recognition.

A 37-year-old woman presented with multifocal ischemic strokes and visceral infarctions. Initial transesophageal echocardiography (TEE) showed a small isoechoic structure on the mitral valve, interpreted as a possible vegetation. Despite empiric broad-spectrum antibiotics and therapeutic anticoagulation, she developed progressive thrombocytopenia, hemolytic anemia, disseminated intravascular coagulation, and multiorgan failure. Repeated blood cultures were negative, and repeat TEE showed no valvular masses. The patient died despite plasma exchange, plasma infusion, corticosteroids, and transfusion support. Postmortem examination revealed previously undiagnosed bilateral metastatic invasive lobular breast carcinoma. Histopathology demonstrated tumor cell-containing fibrin-platelet vegetations on the mitral and tricuspid valves, with fibrin-rich microthrombi in renal arterioles consistent with secondary paraneoplastic thrombotic microangiopathy.

This autopsy-confirmed case underscores that malignancy-associated NBTE may remain echocardiographically occult despite extensive arterial embolization. It also demonstrates that valvular thrombi may incorporate tumor cells, providing a direct substrate for embolic events.