Mitral Valve Infective Endocarditis with Vegetations

A 46-year-old intravenous drug user with rheumatic mitral valve disease presented with 3 weeks of fever, night sweats, and progressive dyspnea. Blood cultures grew Staphylococcus aureus. Transoesophageal echocardiography showed a 1.6 cm mobile vegetation on the mitral valve with severe regurgitation, and he underwent urgent valve replacement. On examination of the explanted valve specimen, the structure marked **A** is most characteristic of which pathological process in infective endocarditis?