Hotspot analysis by confocal microscopy can help to differentiate challenging melanocytic skin lesions

Abstract

Some melanocytic lesions do not present enough clinical and dermoscopic features to allow ruling out a possible melanoma diagnosis. These "doubtful melanocytic lesions" pose a very common and challenging scenario in clinical practice and were selected at this study for reflectance confocal microscopy evaluation and subsequent surgical excision for histopathological diagnosis. The study included 110 lesions and three confocal features were statistically able to distinguish benign melanocytic lesions from melanomas: "peripheral hotspot at dermo-epidermal junction", "nucleated roundish cells at the dermo-epidermal junction" and "sheet of cells". The finding of a peripheral hotspot (atypical cells in 1mm2) at the DEJ is highlighted because has not been previously reported in the literature as a confocal feature related to melanomas.

Fig 1. Superficial spreading melanoma in situ.

(A): Dermoscopy shows atypical network and peppering. (B): RCM mosaic image (8.0 x 8.0 mm) at the spinous layer; visual inspection positioned the hotspot at a central location (1.0 x 1.0 mm square area is marked with yellow dashed outline and better shown in C). (C): Atypical honeycomb pattern and widespread roundish cells (yellow arrows) and dendritic cells (red arrows) in sheet of cells distribution. (D): RCM mosaic image (8.0 X 8.0 mm) at DEJ; visual inspection positioned the hotspot at a peripheral location (1.0 x 1.0 mm square area is marked with yellow dashed outline and better shown in E). (E): Non-edged papillae, roundish cells at DEJ (yellow arrows) and dendritic cells (red arrows) in sheet of cells distribution. (F): Histopathology confirms a superficial spreading melanoma in situ (H&E, original magnification x200), with disarrangement of the rete ridge and increased number of atypical melanocytes affecting the adnexae.

Fig 2. Superficial spreading melanoma.

(A): Dermoscopy shows atypical network and peppering. (B): RCM mosaic image (8.0 x 8.0 mm) at epidermis (suprabasal layer); visual inspection positioned the hotspot at a central location (1.0 x 1.0 mm square area is marked with yellow dashed outline and better shown in C). (C): Atypical cobblestone pattern. (D): RCM mosaic image (8.0 X 8.0 mm) at DEJ; visual inspection positioned the hotspot at a peripheral location (1.0 x 1.0 mm square area is marked with yellow dashed outline and better shown in E). (E): Non-edged papillae, roundish cells at DEJ (yellow arrow) and dendritic cells (red arrows). (F): Histopathology confirms a superficial spreading melanoma (H&E, original magnification x200), with Breslow = 0.55 and presence of pagetoid cells.