Sean Klepper M.D.
Stephen Lyle, M.D., ...
- Most common in children and young adults
- Presents as a well-circumscribed 1- to 2-cm blue to black area of discoloration, most commonly on the buttocks, sacral area or scalp
- Rarely recurs
- Rare transformation to melanoma (malignant blue nevus)
- Cellular lobular mass, or sometimes multiple lobules, centered on the reticular dermis and sometimes extending into the subcutaneous fat
- The inferior margin of the lesion is well defined displays a rounded, bulging appearance.
- At least one third of the lesion is composed of round to oval to fusiform cells with variable amounts of melanin and often relatively clear cytoplasm.
- The cells may show mild pleomorphism and occasional mitoses, but if two or more mitoses per square mm are seen, the lesion should be carefully evaluated for features of malignancy.
- The nevus cells are usually arranged in nests or bundles of fascicles, which may or may not be encapsulated by fibrous tissue.
- The fibrous tissue surrounding the nests often contains pigmented dendritic melanocytes and melanophages.
- Cystic degeneration of the nests is common, particularly in the central aspect of the lesions, secondary to ischemia. Edema, myxoid degeneration, reduced cellularity and increased melanophages are seen.
- Many cases show a component of common blue nevus in addition to the cellular blue nevus pattern ("biphasic pattern").