Actinomycosis is a chronic bacterial infection caused by the microorganism Actinomyces israelii. It is a disease that most commonly affects the face, head, and neck, and can spread to other parts of the body. Histologically, actinomycosis is characterized by granulomatous inflammation that is composed of a mixture of inflammatory cells, including lymphocytes, macrophages, and plasma cells. In addition, multinucleated giant cells, fibroblasts, and vascular endothelial cells are commonly present.
The granulomas are typically found arranged in a stellate pattern and will often contain numerous sulfur granules, which are yellow-gray masses composed of a mixture of bacterial colonies, inflammatory cells, and fibrin. These granules are considered the pathognomonic feature of actinomycosis and are easily visible under light microscopy. The granulomas are also surrounded by a dense layer of fibrous tissue, which is responsible for the formation of abscesses, sinus tracts, and fistulae.
In addition to the presence of sulfur granules, actinomycosis can be diagnosed by the presence of Actinomyces colonies in stained tissue samples. The colonies are gram-positive rods, and often appear in a branching pattern. On culture, they grow slowly and typically form a pale yellow-orange colony.
In summary, the histological features of actinomycosis include granulomatous inflammation composed of a mixture of inflammatory cells, multinucleated giant cells, fibroblasts, and vascular endothelial cells. Additionally, the presence of sulfur granules and Actinomyces colonies are characteristic of the disease.
