Tubercle

The characteristic lesion of tuberculosis is the formation of tubercle which is a small rounded nodule in the tissue . Microscopically , there is central area of necrosis or caseation of tubercle . This is surrounded by nodular collection of epitheloid cells and scattered langhan’s type of giant cells . the epitheloid cells are modified mononuclear cells with a clear cytoplasm and pale vesicular nucleus . A zone of lymphocytes is present around the epitheloid cells . The zone of lymphocytes is surrounded by a zone of fibrous tissue and granulation tissue