Pigmented spindle cell naevus and its variants: distinction from melanoma.

We report seven examples of pigmented spindle cell naevus (PSCN) and variants, emphasizing their histopathologic differentiation from malignant melanoma (CMM). Confusion with CMM may occur because of upward migration (pagetoid spread) of cells, prominent lateral extension of lentiginous melanocytic hyperplasia, and cytological atypia in spindle cell naevi. However, these proliferations are usually associated with a symmetrical and orderly growth pattern, confinement of the pagetoid spread to the lower epidermis, 'maturation' of the dermal component, and lack of marked cytological atypia.