ABSTRACT
Reflectance confocal microscopy (RCM) is a novel in-vivo imaging technique enabling the visualization of cutaneous structures at near histologic resolution from the epidermis to the papillary dermis, which has been shown to improve accuracy in diagnosing melanocytic lesions.21-23 The typical RCM features of Spitz nevi include the presence of sharp border cutoff, junctional nests composed of densely packed melanocytes and presence of melanophages. However, due to the inability of the reflectance confocal microscope to explore the skin clearly at deeper skin levels, a low specificity in differentiating melanomas and Spitz nevi was demonstrated in several publications hampering the evaluation of mitoses and maturation found deeper than the dermo-epidermal junction (DEJ).24-29
RCM findings for Spitz nevi include the presence of pagetoid cells within the epidermis in approximately 50% of cases. These “pagetoid cells” are typically low in number, predominantly located in the center of the lesion, and constituted by small,
elongated cells with short dendritic-like branches. On the other hand melanoma presents with an evident irregular epidermis, roundish pagetoid cells in higher numerosity and atypical melanocytes distributed throughout the DEJ in heterogeneous nests or sheet-like structures.30 Moreover, Spitz nevi contain thin elongated cells with peripheral dendritic processes that are frequently observed in the basal and suprabasal layers corresponding to spindle cells in histology with peripheral clefting (Figure 21.1).31 The lesion periphery may be composed of a rim of dense melanocytic nests correlating with peripheral melanocytic nests sharply demarcating the lesion border in histology. Numerous large melanocytic dense nests are distributed symmetrically in Spitz nevi corresponding to a the globular pattern seen in dermoscopy. Spitz nevi presenting a homogenous diffuse pigmentation and/or pigment network in dermoscopy are predominantly characterized by non-edged papillae at the DEJ, sometimes with the presence of atypical cells within the epidermal basal layer. Numerous plump bright cells, corresponding to melanophages, may be seen in the dermis and blood vessels are frequently observable in the upper dermis. In nodular lesions, large confluent irregular clusters of cells, heterogeneous in shape and reflectivity, can be observed in the upper dermis and correspond to ovoid nests composed of densely clustered large epithelioid cells in histopathology.
