Atypical histological features characteristic of naevi from special sites
| Special site | Architectural distortion | Lentiginous growth | Pagetoid spread | Cellular dyscohesion | Cytological atypia | Dermal mitotic activity | Stromal reaction* | Spindled morphology | Major differential diagnosis | |
| Irregular/confluent junctional nests | Dense dermal growth | |||||||||
| Acral | ++ | − | ++ | ++ | − | ± | − | + | + | Acral lentiginous melanoma |
| Vulvar | + | ++ | + | ± | ++ | ++ | + | ++ | + | Nodular melanoma |
| Breast | + | − | − | + | − | + | − | + | ± | Superficial spreading melanoma |
| Flexural | + | − | − | + | ± | + | − | + | ± | Superficial spreading melanoma |
| Ear and scalp | + | − | + | + | + | + | − | + | ± | Superficial spreading melanoma |
↵* Stromal reaction pattern is usually present as papillary dermal fibroplasia (concentric, lamellar) with an inflammatory infiltrate. However, in vulvar naevi the stromal reaction may be inconspicuous or have a unique pattern showing a broad zone of eosinophilic fibrosis involving much of the dermis ± a variable inflammatory infiltrate.
−, unusual feature; ±, rare or occasional feature; +, common feature; ++, characteristic feature.