Nonbacterial thrombotic endocarditis, gross specimen. Nonbacterial thrombotic endocarditis is usually associated with neoplastic diseases, autoimmune diseases, and valvular diseases. It is characterised by the presence of granular lesions on valve leaflets. The lesions are composed of fibrin and platelet aggregates and lack bacteria or inflammation. The lesions usually affect the mitral valve (shown here) or aortic valve, although any valve can be involved.