Atypical melanocytic lesions

Atypical melanocytic lesions are relatively common and can be difficult to diagnose with confidence. Dysplastic naevi were the first type to be described and have specific features. The pigmented lentiginous naevus with atypia was first described in 1991 but has only recently been more commonly recognized. In situ malignant change is described in a significant proportion of cases. Lesions from special sites may show atypical features, as can recurrent lesions, and the pathologist needs to be aware of the particular changes seen. Dermal nodules may arise in benign naevi and can be suspicious clinically. Combined naevi, mitotically active naevi and ancient naevi may show atypical features. The pathologist needs to document the atypical features seen and to be clear about the implications these features have on the diagnosis and treatment.