Page 462 - Textbook of Pathology, 6th Edition

446

Figure 16.28 Infective endocarditis. A, Location of vegetations on
the valves of the left heart. The vegetations are shown on the mitral
valve (left upper diagram) as viewed from the left atrium, while those on
the aortic valve (left lower diagram) are shown as seen from the left
ventricle. B, Vegetations on valves in infective endocarditis. Opened up
chambers and valves of the left heart show presence of irregular, soft,
elevated grey white friable vegetations on the atrial (superior) surface of
the mitral valve (arrow).

3. Impaired host defenses: All conditions in which there is Grossly, the lesions are found commonly on the valves of
depression of specific immunity, deficiency of complement the left heart, most frequently on the mitral, followed in
and defective phagocytic function, predispose to BE. descending frequency, by the aortic, simultaneous
Following are some of the examples of such conditions:
i) Impaired specific immunity in lymphomas. involvement of both mitral and aortic valves, and quite
ii) Leukaemias. rarely on the valves of the right heart. The vegetations in
iii) Cytotoxic therapy for various forms of cancers and trans- SABE are more often seen on previously diseased valves,
SECTION III
plant patients. whereas the vegetations of ABE are often found on
iv) Deficient functions of neutrophils and macrophages. previously normal valves. Like in RHD, the vegetations
are often located on the atrial surface of atrioventricular
PATHOGENESIS. Bacteria causing BE on entering the valves and ventricular surface of the semilunar valves.
bloodstream from any of the above-mentioned routes are They begin from the contact areas of the valve and may
implanted on the cardiac valves or mural endocardium extend along the surface of the valves and on to the
because they have surface adhesion molecules which mediate adjacent endocardium (Fig. 16.28).
their adherence to injured endocardium. There are several The vegetations of BE vary in size from a few
predisposing conditions which explain the development of millimeters to several centimeters, grey-tawny to greenish,
bacterial implants on the valves: irregular, single or multiple, and typically friable. They
1. The circulating bacteria are lodged much more frequently may appear flat, filiform, fungating or polypoid. The
Systemic Pathology
on previously damaged valves from diseases, chiefly RHD, vegetations in ABE tend to be bulkier and globular than
congenital heart diseases and prosthetic valves, than on those of SABE and are located more often on previously
healthy valves. normal valves, may cause ulceration or perforation of the
2. Conditions producing haemodynamic stress on the valves underlying valve leaflet, or may produce myocardial
are liable to cause damage to the endothelium, favouring abscesses.
the formation of platelet-fibrin thrombi which get infected Microscopically, the vegetations of BE consist of 3 zones
from circulating bacteria.
(Fig. 16.29):
3. Another alternative hypothesis is the occurrence of non- i) The outer layer or cap consists of eosinophilic material
bacterial thrombotic endocarditis from prolonged stress which composed of fibrin and platelets.
is followed by bacterial contamination.
ii) Underneath this layer is the basophilic zone containing
MORPHOLOGIC FEATURES. The characteristic patho- colonies of bacteria. However, bacterial component of the
logic feature in both ABE and SABE is the presence of vegetations may be lacking in treated cases.
typical vegetations or verrucae on the valve cusps or iii) The deeper zone consists of non-specific inflamma-
leaflets, and less often, on mural endocardium, which are tory reaction in the cusp itself, and in the case of SABE
quite distinct for other types. A summary of the there may be evidence of repair.
distinguishing features of the principal types of vegetations In the acute fulminant form of the disease, the inflam-
is presented in Table 16.8. matory cell infiltrate chiefly consists of neutrophils and is