Common Blue Nevus with Satellite Lesions Needs a Differential Diagnosis from Malignant Melanoma
A healthy 24-year-old Japanese man was referred to our hospital with a blue-black skin lesion on his left forearm. As confirmed by the patient, this lesion had developed after he accidentally pricked his forearm with a pencil 13 years earlier. Physical examination revealed a 10 × 7-mm, blue-black nodule with an irregular border, which was accompanied by 1–2-mm guttate macular satellite lesions (fig. ). Dermoscopic examination showed a homogeneous, blue-white structure in the absence of any other dermoscopic structures (fig. ). An excisional biopsy was performed with the suspicion of a common blue nevus versus a malignant melanoma. The lesion was excised with a 3-mm margin of surrounding normal skin down to the level of the superficial fascia. We recognized a black-colored restiform structure in the dermis during the operation and added another 3-mm margin. In the histopathological examination of the excised lesion, nevus cells were dispersed in the dermis, and hyperpigmented, spindle-shaped melanocytes infiltrated among the collagen bundles (fig. ). Periappendageal and perivascular concentrations of the nevus cells were observed (fig. ). Similar findings were observed in the satellite lesions as well (fig. ). There were no features suggestive of malignancy, such as cytological atypia, atypical mitoses or necrosis. A histological diagnosis of common blue nevus was then rendered.