Dermal melanocytoses and variants

Dermal melanocytoses form a spectrum of benign intradermal melanocytic lesions composed of dendritic melanocytes, the most common of which is the blue naevus. A variety of clinical and histological appearances may be assumed, some of which can be worrisome both to the clinician and pathologist, with the most difficult differential diagnosis, in some instances, lying with malignant melanoma. This review presents and discusses the spectrum of histological appearances of this diverse group of lesions, and highlights the clinicopathological variants which are most likely to cause diagnostic difficulty. The lesions that form this spectrum and therefore will be discussed include the dermal melanocytoses such as the Mongolian spot, blue naevus and its variants, deep penetrating naevus, melanoma arising within a blue naevus and, finally, although not a member of this group, cutaneous metastatic melanoma mimicking blue naevus.