Pictured is a surgically resected aortic valve from a 47-year-old man.
The gross pathology shows lobulated, friable red-tan heterogeneous vegetations involving all cusps. The cusp on the right side of the image shows damage inferiorly by the vegetation. This combination of vegetations with concomitant tissue damage is virtually pathognomonic for infective endocarditis.
What is the most common organism causing infective native valve endocarditis? This reference studied 310 valves, with 44 different organisms (https://www.sciencedirect.com/science/article/pii/S1054880712000610).“The four most commonly identified organisms were viridans group streptococci (28%), Staphylococcus aureus (18%), enterococci (9%), and coagulase-negative staphylococci (8%).” All of these are Gram-positive cocci.
With regard to the differential diagnosis, non-bacterial thrombotic endocarditis (NBTE; choice C) is sterile and composed of platelets and fibrin. It’s associated with underlying hypercoagulable conditions such as autoimmune disorders and malignancy. The mitral valve is most commonly affected, followed by the aortic valve in frequency. NBTE classically occurs along the lines of closure of the valve. The endocardial irritation that occurs in that location may serve as a nidus for development. They tend to have a smoother contour, are usually more uniformly red in coloration, and do not cause underlying valve damage. They have a “stuck on” appearance, rather than an erosive one.
Papillary fibroelastoma/ Lambl excrescence (PFE / LE) was also in the differential (choice D). The projection emanating from the bottom cusp is suspicious for this. However, PFE/LE does not cause underlying valve damage, and (2) the associated vegetations are not in keeping with this diagnosis. Here’s a gross photo for reference.