The differential diagnosis of heavily pigmented melanocytic
neoplasms includes
melanoma (especially animal type),
melanosis of partially or completely regressed
melanoma, blue naevus (BN), pigmented Spitzoid lesions, recurrent naevus, combined naevus, pigmented spindle cell naevus, epithelioid blue naevus of the
Carney complex/pigmented epithelioid melanocytoma, deep penetrating naevus, hyperpigmented
scar after surgery of
melanoma in which there are also melanophages and
hyperpigmentation due to the
minocycline, a
tattoo or a hyperpigmented
scar. Pathologists face challenges when evaluating a pigmented lesion, especially in a small superficial biopsy, because it is difficult to access important histopathological features to differentiate benign versus malignant melanocytic lesions. The histological features that favour a diagnosis of
melanoma include dimension (>6 mm), asymmetry, poor circumscription, irregular confluent nests, confluent lentiginous junctional melanocytic proliferation, lack of maturation with descent in the dermis, suprabasal pagetoid melanocytes, asymmetrical distribution of
melanin pigment, cytological atypia, dermal mitotic figures, asymmetrical dermal lymphocytic infiltrate and
necrosis.