Gummas are granulomatous, rubber-like lesions that can occur in the tertiary stage of syphilis on the liver, heart, brain, skin and other organs. These have a necrotic center that is caused by tissue clotting necrosis in response to spirochaetes and that is surrounded by an inflammatory fibroblast and a zone rich in capillaries. Lymphocytes and plasma cells may also occur in the peripheral part. As time goes by, gummas can degenerate to become fibrous and leave an irregular scar or fibrous knot.
Here are some other gummas pictures:
Gumma of liver 1
Gummas of brain: 1 and 2