Histology of congenital nevi during the first year of life. A study by conventional and electron microscopy.

We studied 14 biopsies of congenital melanocytic nevi of children up to 1 year of age. In 11 biopsies we found two different types of melanocytic cells. In the reticular dermis, they were small cells. They had small nuclei, little cytoplasm, and no detectable pigment. They did not come in nests, but were scattered between the collagen bundles. The other type of cells was found within the epidermis or closely under it. These cells were large and round, and had abundant cytoplasms and evenly distributed melanin. Sometimes these cells were arranged in nests and in two moles they were also found in the epithelia of follicles. In all of these biopsies (with three exceptions) the superficial, large pigmented cells were separated from the deep, small, nonpigmented ones by a zone of tissue without any melanocytic cell. Early in life both types of cells are clearly separated, and the superficial ones are few. At later ages the superficial large cells are found in increased numbers, whereas the number of the deep ones does not change with age.