Benign Melanocytic Lesions

The blue nevus (BN) is a distinct benign melanocytic nevus subtype with characteristic clinical, dermoscopic, and histopathologic features. The features seen in BN can sometimes overlap with features seen in nodular/dermal melanoma and melanoma metastasis. In addition, variants of BN such as cellular blue nevi, deep penetrating blue nevi, and sclerosing blue nevi can be confused with melanoma. The most characteristic pattern of BN is the presence of homogeneous and structureless blue pigmentation. The histopathologic variants of BN are defined primarily based on their cellularity and stromal fibrotic reaction. Congenital melanocytic nevi, malignant BN, nodular melanoma, melanoma metastasis, exogenous tattoos (i.e., radiotherapy tattoos), or pigmented spindle-cell nevi (Reed's nevi) can be indistinguishable from BN. Other nonmelanocytic tumors, such as basal cell carcinomas, hemangiomas, angiokeratomas, and up to 20% of pilomatrixomas, may present with confluent bluish pigmentation, but other clinical and dermoscopic clues are often evident to assist in making the correct diagnosis.