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Infective Endocarditis - Gross

Mitral and aortic valves are most commonly affected in cases of NVE, accounting for 90-95% of cases. Right-sided valves are rarely involved except in injection drug users (IDU). More than one valve is infected in 15-20% of cases.

Vegetations are most commonly seen on the line of closure of a valve, that is, on the atrial surface of mitral and tricuspid valves and on the ventricular surface of the semilunar valves. They are often tan gray in color and friable, variable size and may be polypoid, verrucous or plaque-like.

Rarely, vegetations are so bulky to cause valvular obstruction. Vegetations are often single in the mitral valve but often affect more than one cusp of the aortic valve in areas of direct apposition.  Mural endocarditis is often due to opportunistic fungal infections and involves multiple cardiac chambers (Figure 1 and 2).  The vegetations may be red-brown or yellow-white raised lesions that are several millimeters in diameter.

Valvular regurgitation can result from several mechanisms: failure of leaflet coaptation due to large vegetations, extensive tissue destruction that lead to leaflet perforation or avulsion, and chordal rupture . Tissue destruction can also lead to saccular outpouching in the valve called an aneurysm or diverticulum that often becomes perforated at the dome (Figure 4). With organization and healing, the valve can be deformed and thickened.  The previous infection can also result in perforations with smooth slightly raised borders in the body of the cusp or leaflet.

The central location of the aortic valve at the base of the heart explains the path of infection and the complications that arise from local extension. The infection may spread to the valve annulus resulting in an annular abscess.

Development of abscess may lead to aneurysm of the sinus of Valsalva, infiltration of the interventricular septum, and fistula formation with the right atrium or right ventricle resulting in intracardiac shunting . Rupture of an abscess cavity may lead to pericarditis and bleeding that result in cardiac tamponade. Destruction of the conduction system along the interventricular septum can cause a complete heart block.  An aortic valve infection can also extend to the anterior mitral valve leaflet because of the mitro-aortic continuity.

Vegetations most frequently embolize to the brain, heart, spleen and kidneys.  Emboli can cause tissue infarction and is particularly devastating in the coronary and cerebral circulation.  An infected embolus can cause an arteritis that leads to the development of a mycotic aneurysm.

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