Localization and frequency of lesions
Inflammation can affect different structures of the inner lining of the heart. Three main localizations are distinguished:
- Valvular endocarditis — occurs most frequently, affecting the cusps and leaflets.
- Chordal endocarditis — inflammation spreads to the tendinous cords.
- Mural (parietal) endocarditis — involves the endocardium of the atrial or ventricular walls.
The frequency of valve involvement is distributed unevenly. The absolute leader is the mitral valve (65–70% of cases). In second place is combined involvement of the mitral and aortic valves (about 25%). Isolated aortic valve involvement is less common, tricuspid involvement is significantly rarer, and pulmonary valve involvement is considered a casuistry.
Initial forms: from valvulitis to thrombus formation
Morphological changes in rheumatic fever represent a unified, interrelated process that goes through several stages.
- Diffuse endocarditis (valvulitis). This is an early stage in which the endothelium remains intact, therefore thrombotic deposits are absent. Macroscopically, the cusps appear unevenly thickened, grayish, and translucent along the line of closure. Under the microscope, mucoid swelling, moderate fibrinoid changes, and lymphohistiocytic infiltration are visible. Specific rheumatic granulomas may form deep within the tissue. With timely treatment, this process is completely reversible.
- Acute verrucous endocarditis. If the process progresses, fibrinoid changes intensify, and endothelial necrosis occurs. Small 1–2 mm thrombi—"verrucae"—settle on the damaged areas (along the cusp closure margin). Initially gray and translucent, they subsequently become opaque and yellowish-gray. These thrombotic masses are easily dislodged. Outside the "verrucae" zone, the valve tissue appears unchanged.
Progressive forms: sclerosis and relapses
- Fibroplastic endocarditis. This is a consequence of the first two forms. Active sclerosis processes come to the foreground. The valve tissue thickens and acquires a gray, translucent appearance, though its density has not yet reached its maximum. Microscopically, connective tissue disorganization and inflammatory infiltration are observed. Fresh thrombi may appear, with no temporal gap between old and new changes.
- Recurrent verrucous endocarditis. Occurs during repeated rheumatic attacks. The process unfolds against the background of already altered, sclerosed, and deformed valves. Inflammation and disorganization involve both the intact stroma and old scar tissue. On the sclerosed masses, the endothelium is damaged again, and fresh portions of fibrin are deposited, which also undergo sclerosis as the process subsides.
Complications and outcomes
Verrucous forms (acute and recurrent) are characterized by a formidable complication — thromboembolism of the systemic circulation. Detached thrombotic masses lead to infarctions of the spleen, kidneys, brain, myocardium, and retina. In some cases, gangrene of the intestine or lower extremities develops.
A natural outcome of the inflammation is the development of a heart defect. Valve tissue undergoes sclerosis and hyalinosis. The cusps thicken, shorten, and deform.
- Semilunar cusps (aorta, pulmonary artery) curl along their free edges and may fuse with the vessel wall.
- Mitral valve undergoes gross changes: the anterior and posterior cusps fuse, and the boundaries between them are erased. A dense fibrous funnel is formed, and the orifice itself narrows into a narrow slit or sickle. The chordae tendineae also thicken, shorten, and fuse together.
Functionally, these changes manifest as stenosis (narrowing of the orifice), insufficiency (incomplete closure), or a combination of both, which is most common.
Briefly: answers to topical questions
What cells are part of the specific rheumatic granuloma (Aschoff-Talalaev granuloma)?
The specific rheumatic granuloma consists of macrophages, lymphocytes, plasma cells, fibroblasts, and specific giant cells.
Cellular elements include:
- Anichkov cells — large epithelioid cells with basophilic cytoplasm and a characteristic nuclear appearance ("owl-eye" or "caterpillar").
- Aschoff cells — multinucleated giant histiocytes.
- Macrophages — actively secrete cytokines and growth factors.
- T-lymphocytes and B-lymphocytes — participate in immune responses.
- Plasma cells — present in the inflammatory infiltrate.
- Fibroblasts — appear at the stage of the "fading" granuloma.
What blood elements make up the thrombotic deposits ("verrucae") in rheumatic endocarditis?
Thrombotic deposits ("verrucae") in rheumatic endocarditis consist of fibrin and thrombotic masses.
They form along the closing margin of the valve cusps when the endothelium is involved and damaged. During repeated rheumatic attacks, new masses of fibrin are deposited on old sclerosed thrombotic masses.
Which histological layers of the valve cusp are involved in the pathological process in rheumatic fever?
In rheumatic fever, the endothelium, subendothelial layer, and deep layers of the valve cusp are involved in the pathological process.
Depending on the form of endocarditis, the following are affected:
- Endothelium — in diffuse endocarditis, endothelial damage is absent; in acute verrucous endocarditis, endothelial necrosis develops with the formation of thrombotic deposits; in recurrent verrucous endocarditis, the endothelium is involved in the inflammatory process.
- Subendothelial layer — fibrinoid changes are described within it; mucoid swelling, moderate fibrinoid changes, and lymphohistiocytic infiltration are also noted during valvulitis.
- Deep layers of the cusps — may contain lymphohistiocytic infiltration and rheumatic granulomas; fibroplastic processes, connective tissue disorganization, and inflammatory infiltration are noted in fibroplastic endocarditis.
The phrase "Even Acute Fibrin Returns" (Diffuse, Acute verrucous, Fibroplastic, Recurrent verrucous) helps remember the 4 stages of morphological changes.
Class and exam questions
Why do thrombi not form in valvulitis?
In diffuse endocarditis (valvulitis), the integrity of the endothelial layer is preserved. Without endothelial necrosis, there are no conditions for fibrin deposition and thrombotic mass formation.
How to distinguish fibroplastic endocarditis from recurrent verrucous endocarditis?
In the fibroplastic variant, there is no time interval between old changes and fresh thrombi. Recurrent verrucous develops during repeated attacks against the background of already formed sclerosis and valve deformation.
What is the main danger of verrucous forms of endocarditis?
The main threat is the detachment of thrombotic deposits ("verrucae"), leading to systemic thromboembolism. This causes internal organ infarctions and gangrene.
What does the mitral valve look like macroscopically as an outcome of the disease?
Valve cusps become sclerosed and fuse together, forming a dense fibrous funnel. The valve orifice narrows sharply, acquiring a slit-like or sickle shape.
What else to study on this topic
- Microscopic structure and cellular composition of rheumatic granulomas.
- Stages of connective tissue disorganization: from mucoid swelling to hyalinosis.
- Pathogenesis of hemodynamic disorders in mitral stenosis and insufficiency.
- Mechanisms of organ infarction in the systemic circulation during thromboembolism.
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