Epidermoid cyst of the scalp containing human papillomavirus.
We report an epidermoid cyst of the scalp with light microscopic and immunohistochemical evidence of human papillomavirus (HPV) infection. Light microscopic features suggesting HPV infection included papillomatosis and hypergranulosis of the cyst lining with the presence of koilocytes. Much of the keratin within the cyst demonstrated parakeratosis. Immunoperoxidase labeling for HPV antigen was noted within koilocytes. Papillomavirus infection has been reported in plantar epidermoid cysts. To our knowledge, this is the first report of a papillomavirus-infected epidermoid cyst in a site other than plantar skin. Light microscopic features of our cases differed from those of the plantar cysts. Epidermoid cysts may be induced by the papillomavirus or the virus may merely infect pre-existing cysts.