So many naevus and melanoma variants! Split or lump?
A cellular blue naevus looks nothing like a Spitz naevus, or indeed like a compund naevus NOS (not otherwise specified). The presence of mitotic figures at the deep base of a lesion otherwise resembling a Spitz naevus in an adult is of some concern, but the same number of mitotic figures in a cellular blue naevus is not suspicious at all. Divergent cell types are encountered in many melanomas, but also in combined naevi, balloon cell naevi and recurrent naevi. Ascent of melanocytes into the upper cell layers of the epidermis is common in melanomas, but is also found in many Spitz naevi, Reed naevi, acral naevi, and in congenital naevi in early childhood.
Thus, the interpretation of individual findings - mitotic activity, divergent cell types, mitotic activity, and many other parameters - depends on the differential diagnosis that is relevant in the case at hand. In melanocytic tumour pathology, there are few, if any, generally applicable indicators of malignancy or benignity. For this reason, a good working knowledge of the histological features of each of the many naevus en melanoma subtypes is indispensable. The pathologist, when studying a melanocytic neoplasm, should not just ask himself: is this a naevus or a melanoma?, but should decide on the relevant naevus and melanoma subtypes to be considered in that particular instance, and should apply the diagnostic criteria that relevant in that particular setting.
This is no easy task, and it is the reason why handbooks on melanocytic pathology, including the one written by Professor Thomas Krausz and myself, tend to be substantial, sometimes bulky, books. One just cannot omit the details, because in the differential diagnosis of melanocytic lesions, the devil is in the details. One cannot do without them. We all need to be splitters, in this area of pathology.
In the next section, a limited number of common melanocytic lesions will be presented and discussed. The main part of this website, the slide collections, contains many more variants, and will present the features that allow recognition of the many entities and variants. The slide sets are grouped under a limited number of headings, but within each set, there is no particular order. If you are interested in a particular entity or variant, the search function of the website allows you to go directly to examples of it.