Perineural Pattern of Aggregation of Cellular Blue Nevus : Probable Histoarchitectural Reminiscence of Histogenesis

A striking feature of cellular blue nevus consists in the presence, in its histologic picture, of numerous hypertrophic nerves and nerve-like figures, positive for histochemical and immunohistochemical methods for nerve fibers and myelin sheaths. These findings, first described in Masson's original article and repeatedly highlighted in the past for their possible histogenetic significance, are currently considered as merely coincidental. However, the thin conventional histologic sections, catching only short tracts of the nerves, preclude a correct observation of their route and do not allow us to verify if there is an architectural relationship between them and the nevus as a whole. With this aim, we observed a few specimens of cellular blue nevus on digitally overlapped images of contiguous 25-μm-thick sections, processed with Winkelmann's technique of silver impregnation for nerve fibers, which supplied an overall, 3-dimensional view of the lesions and the nerves running through them. In these images, the lobular form of the nevus could be seen gathering around a branching hypertrophic nerve, whose stem stretched vertically from the depth to the most superficial tract of the lesion. The nevus cell aggregates invested the stem and the limbs individually, and these followed the curvilinear contour of the nevus lobules. Our images represent evidence of a preferential perineural aggregation of cellular blue nevus, at least in its lobular form. This indicates that the numerous nerves and the neuroid figures, observed in detail-but within a limited perspective- in the conventional sections, are not merely coincidental and they could indeed be a sign of neural differentiation and/or a clue to the possible neural origin of the nevus.