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In medicine (anatomical pathology), a granuloma is a group of epithelioid macrophages surrounded by a lymphocyte cuff. Granulomas are small nodules that are seen in a variety of diseases such as Crohn's disease, tuberculosis, sarcoidosis, berylliosis and syphilis. It is also a feature of Wegener's granulomatosis and Churg-Strauss syndrome, two related autoimmune disorders.
An important aspect of granulomas is whether they are caseating or not. Caseation (literally: turning to cheese) is a form of necrosis at the centre of a granuloma and is a feature of the granulomas of tuberculosis.
Tuberculous granuloma
The tuberculous granuloma (caseating tubercule): central caseous necrosis bordered by giant multinucleated cells (Langhans cells), and surrounded by epithelioid cells aggregates, lymphocytes and fibroblasts. Granulomatous tubercules tend to confluence. Multinucleated giant cell (mature - Langhans type): 50-100 micrometres, numerous small nuclei (over 20) disposed at the periphery of the cell (crown or horseshoe), abundant eosinophilic cytoplasm. It results when activated macrophages merge. Epithelioid cells are activated macrophages resembling epithelial cells: elongated, with finely granular, pale eosinophilic (pink) cytoplasm and central, ovoid nucleus. They have indistinct shape contour and form aggregates. At the periphery are the lymphocytes (T cells) and rare plasma cells and fibroblasts. Caseous necrosis is a central area, amorphous, finely granular, eosinophilic (pink). If recent, it may contain nuclear fragments. The caseum is the result of the accumulated destruction of giant cells and epithelioid cells.
Chronic granulomatous disease
In the rare condition chronic granulomatous disease, neutrophil granulocyte function is impaired and granulomas form in various organs in response to infection, as the infection is not being contained through normal means.
Sarcoidose granulomas
Sarcoidose granulomas are nodal aggregates of epitheloid cells, similar to epitheolid tubercules of tuberculosis. However, the quantity of necrosis is low and it is noncaseating. Multinucleated giant cells of Langerhans cell type and foreign-body type giant cells are present, however they are less numerous and can be star-shaped (asteroid bodies) or lamellar (Schaumann bodies). These inclusions are not sarcoidose-specific. Some fibrous tissue and lymphocytes are present on the periphery. These granulomas can resorb or heal with a scar. In the lungs this can cause disseminated pulmonary fibrosis; in cardiac tissue they may cause impaired heart function and possibly death by heart failure.
Rheumatic myocarditis
Rheumatic fever affects all the heart tissue (rheumatic pancarditis). From all the pathological changes, only the granulomas, called Aschoff granulomas, are pathognomonic. In the centre, the fibrinoid necrosis is visible. It is encompassed by lymphocytes, plasma cells, fibroblasts and individual neutrophils. Also mononuclear Anitschkow's cells (histiocytes) and the characteristic Aschoff cells are present. Anitschkow's cells appear like an owl's eye and have a pale eosinophilic cytoplasm with a characteristic "caterpillar" nucleole in the bright blistered nucleus. They are arranged in a pallisade around the centre. Aschoff cells have a single or multiple bean-shaped nuclei. Peripherally, fibroblasts and sclerotic fibrous tissue can be seen. The granuloma sometimes borders immediately on partially fragmented muscle fibers.
Gumma hepatis
The less common form of the third stadium of syphilis. Gummas are of different sizes: smaller ones are milliary and more numerous, while the larger ones that are more common, are solitary and elastic. Gumma can develop in different tissues and organs, especially in bones, brain, liver, skin, testis and elsewhere. Contrary to the tuberculous granuloma, in the elastic coagulative central necrosis of the gumma, which is eosinophilic and of grey yellowish colour, there is still some silhouette of the previous tissue visible. The granuloma is encompassed by the grey whitish fibrous envelope, that sometimes sends radial ribbons in the surrounding area. Inbetween, there are lymphocytes, plasma cells and giant cells from capillaries and rare epitheloid cells, and on the periphery lymphocytes and plasma cells are present. By healing, gumma transforms in a large scar that can for example disfigure liver with deep furrows (hepar lobar syphiliticum).
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