Gummas have a firm, necrotic center surrounded by inflamed tissue, which forms an amorphous proteinaceous mass. The center may become partly hyalinized. These central regions begin to die through coagulative necrosis, though they also retain some of the structural characteristics of previously normal tissues, enabling a distinction from the granulomas of tuberculosis where caseous necrosis obliterates preexisting structures. Other histological features of gummas include an intervening zone containing epithelioid cells with indistinct borders and multinucleated giant cells, and a peripheral zone of fibroblasts and capillaries. Infiltration of lymphocytes and plasma cells can be seen in the peripheral zone as well. With time, gummas eventually undergo fibrous degeneration, leaving behind an irregular scar or a round fibrous nodule.
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