Aschoff's bodies or nodules are characteristic lesion of acute rheumatic fever.
These are usually located in the interstitial tissue of the heart, specially in the myocardium and the endocardium often close to small blood vessels. Occasionally, they are present in the pericardium. These have been described in the adventitia of the aorta. Lesions elsewhere in the body may be suggestive of but should not be confused with Aschoff bodies.
Aschoff bodies have been found in a significant proportion of atrial appendages.
Aschoff nodules are globular, elliptic, or fusiform microscopic structures.
There are three phases in the development of the Aschoff body :
1. Early (exudative, degenerative) phase:
2. Intermediate (proliferative or granulomatous) phase:
3. Late (fibrous or healing) phase:
In the granulomatous stage of the lesion the Aschoff body is identifiable and is regarded as pathognomonic for rheumatic carditis.
The early phase of the life cycle of the Aschoff body occur upto the fourth week of acute rheumatic fever is representated by exudative degenerative and fibrinoid changes in the collagenous tissue.
In the intermediate phase which is evident during the fourth to the thirteenth week of the disease swelling and fragmentation of collagen fibres and fibrinoid change are present in the nodule, but cellular proliferation is the main feature. There is accumulation of Anitschkow cells.
Anitschkow cells: These are large mononuclear cells that are found in normal hearts but are increased in number in Aschoff bodies. By themselves they do not represent a specific response to rheumatic fever. The caterpillar chromatin pattern of the nucleus in longitudinal section and owl-eye appearance in transverse section characterize the Anitschkow cell of Aschoff bodies in rheumatic heart disease.
Aschoff cells: (modified Anitschow cells) These are large cells with abundant basophilic cytoplasm ragged cell borders and one to four nuclei.
Other cells usually seen are lymphocytes , plasma cells and occasional neutrophils. As this phase progresses, the exudative and fibrinoid alterations gradually disappear.
In 3 to 4 months the healing phase is reached charcterized by regression and fibrosis of the nodule.
The Aschoff body is elongated or fusiform, the cytoplasm of the component cell is diminished in amount, the cells become elongated and spindle-shaped. Often fibrillar material appears between the cells, crowding them into rows. The collagenous fibers fuse to form dense collagenous bundles resulting in small scars between muscle bundles.
A recent immunohistochemical analysis of the Aschoff lesions in rheumatic fever, combining immunohistochemical analysis with comparative morphology, permitted the division of the Aschoff nodules into three stages:
(1) Aschoff nodule without admixed lymphocytes,
(2) Aschoff nodules with a few T lymphocytes, and
(3) Aschoff nodules containing many admixed lymphocytes of both B- and T-cell phenotype.
It was postulated that the order of progression was from stage 1 with macrophages only, to accumulation of first T lymphocytes (stage 2) and then B lymphocytes (stage 3).
The nature of Aschoff body is a controversial subject:
1) It is a generally accepted view that changes that changes in the ground substance and collagen fibers are primary and precede the formation of Aschoff cells. The Anitschkow cell from which Aschoff cell is derived is considered to be a cardiac histiocyte.
2) According to other investigators Aschoff bodies originate and evolve from primary injury to muscle cells in the heart. In this view Aschoff bodies are lesions of small groups of heart muscle fibers interspersed among other uninvolved bundles of heart muscle fibers. Anitschkow and Aschoff cells are considered to be derived from cardiac myocytes rather than connective tissue cells. Endocardial Aschoff bodies are considered to be lesions of smooth muscle cells which normally occur in the zone between endothelium and myocardium.
3) According to some authors the Aschoff bodies are derived from diseased lymphatic vessels. In this view, proliferation of the endothelial cells of lymphatics give rise to the Aschoff cells.
4) Finally according to some investigators Aschoff bodies are derived from nerves and they have observed close anatomic relationship between nerves and Aschoff bodies.