ABSTRACT
Junctional nevi are characterized by a proliferation of melanocytes, which is confined to the epidermis. Under RCM, the melanocytes can be seen as nests or as small bright cells, mostly along the epidermal basal layer. The suprabasal layers are usually lacking a notable infiltration of melanocytes,1 showing a regular honeycomb or cobblestone pattern, and infrequently, isolated fine dendritic cells that may correspond to Langerhans cells. At the dermal-epidermal junction (DEJ), two main architectural patterns can be identified under RCM mosaic images (akin to low magnification overview on histopathology): the “ringed pattern” and the “meshwork pattern.” These patterns can appear alone or in combination.3-5
Ringed pattern This is the more commonly observed RCM pattern of common junctional nevi. The ringed RCM pattern is seen in mosaic images when there is a predominance of “edged papillae” at the DEJ (Figure 19.1). Dermal papillae show well-demarcated rings lined by bright, small, round to polygonal cells corresponding to both basal keratinocytes and small melanocytes; at the center of the papillae, delicate reticulated collagen fibers can be seen, as well as sometimes blood flow in capillary loops. Scattered, plump, bright cells and small, bright dots (compatible with melanophages and other inflammatory cells) can also be seen in the dermal papilla. Small, dense nests can be observed at the basal layers or bulging into the dermal papillae, but there is predominance of bright cells as solitary units compared with nests. The ringed pattern correlates histopathologically with a predominantly lentiginous proliferation of melanocytes along an undulating DEJ that shows minimal distortion of the
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