Clinical Features:

• 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)

Histologic Features:

• 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").

Cases associated with this book:

Cellular blue nevus
Author: Stephen Lyle, M.D., Ph.D.

Conference: Dr. Z's Consultations