Areas involved include the vulva, vagina, cervix, urethra, anal canal, perineum and perianal skin.
The lesions may be flat but are usually exophytic, solitary but more frequently multiple and focal or extensive. The virus invades the basal cells of the stratified squamous epithelium and establishes a virus-driven stimulation of cell replication. The virus-infected keratinocytes have a distinct morphology referred to as koilocytosis. These cells serve as markers of HPV infection and are produced by viral cytopathic effect. Note the circled koilocytes, one of which is being exfoliated.