Exogenous and endogenous cutaneous anomalies and curiosities.

Exogenous and endogenous substances can produce some interesting cutaneous abnormalities. Exogenous lesions are externally introduced materials or foreign bodies. Endogenous lesions are substances that result from tissue host response to an injury or physical insult. There may be an overlap of these endogenous and exogenous lesions such that externally introduced materials can lead to peculiar tissue reactions. Pathologists should be aware of these anomalies as many of them can simulate neoplasms (ie, Monsel's reaction, polyvinylpyrrolidone disease, silica reaction) and inflammatory (ie, paraffinoma) and infectious processes (ie, Drysol(R) reaction and Lycopodium granuloma). The most interesting and important entities within each of these categories are presented with essential clinical and pathologic descriptions.