ABSTRACT
The final section of this book deals with lesions occurring outside the skin. In this first of the two chapters, those lesions that are unequivocally of melanocytic lineage are discussed. With a few exceptions, they arise in body sites known to harbor melanocytes (juxtacutaneous mucous membranes and associated glands; uveal tract; meninges) or they may be involved by direct extension from an adjacent site harboring melanocytes. The cells from which melanocytic lesions of lymph nodes arise may well have arrived via lymphatic spread from the skin. The possibility of melanocytic differentiation of multipotential stem cells derived from the circulation should be mentioned, although there is no direct evidence of such a scenario at this moment. It might account for the rare occurrence of presumed primary melanomas in deep visceral organs. In the latter situation, however, the possibility of visceral metastasis of a primary melanoma that has completely regressed or otherwise escapes detection seems a plausible alternative.
