Infections of mechanical prosthetic valves usually begin in the sewing ring and spread to the annulus resulting in ring abscess, dehiscence and paravalvular leak. Ring abscesses are more common in infected mechanical valves than in bioproshetic valves. Rupture of ring abscess into the pericardial space is followed by purulent pericarditis. Thrombi on mechanical or bioprosthetic valves should be sampled to rule out endocarditis.
Infections of bioprosthetic valves can involve the cusps and / or the sewing ring.  Vegetations on bioprosthetic valves involve both surfaces of the cusp. Sometimes vegetations can be small and on gross examination there is only fine granularity on the surface of the cusps. Fungal endocarditis typically results in large vegetations. 

Early bioprosthetic valve endocarditis is complicated by rupture of the sinus of Valsalva with perivalvular abscess formation. The endocarditis is a result of contiguous spread from sternal wound infection by Staphylococcus aureus.


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