Foreign Body Reactions

Foreign substances, when injected or implanted accidentally into the skin, can produce a nonallergic foreign-body reaction or, in persons specifically sensitized to them, an allergic response (. In addition, certain substances formed within the body may produce a nonallergic foreign-body reaction when deposited in the dermis or subcutis. Such endogenous foreign-body reactions are produced, for instance, by urates in gout and by keratinous material in pilomatricoma, as well as in ruptured epidermoid and trichilemmal cysts.

Histopathology.

A nonallergic foreign-body reaction typically shows a granulomatous response marked by histiocytes and giant cells surrounding foreign material. Often, some of the giant cells are of the foreign-body type, in which the nuclei are in haphazard array. In addition, lymphocytes are usually present, as may be plasma cells and neutrophils. Frequently, some of the foreign material is seen within macro phages and giant cells, a finding that of course is of great diagnostic value. The most common cause of a foreign-body granuloma is rupture of a hair follicle or follicular cyst, and sometimes only the cyst contents, rather than residual cyst wall, is identifiable . Exogenous substances producing nonallergic foreign-body reactions include silk and nylon sutures ,

wood or other plant material , paraffin and other oily substances, silicone gel, talc, surgical glove starch powder, and cactus spines. Some of these substances-nylon sutures, wood, talc, surgical glove starch powder, and sea urchin spines-are doubly refractile on polarizing examination. Double refraction often is very helpful in localizing foreign substances. Knife marks in the section may be an additional clue to the presence of particulate foreign matter