M 65, scalp. Figs (3)
Microscopic finding: Dermal nevus cells with lipomatous infiltration
Diagnosis: Lipomatous dermal melanocytic nevus (Dermal melanocytic nevus with fatty infiltration)
Congenital melanocytic nevus may show fatty infiltration.
In adults, many melanocytic nevi show fatty infiltration that correlates with age.
Origin of the fatty cells remain uncertain. Possibilities include presence of nevus lipomatosus in melanocytic nevi, fatty metamorphosis of nevus cells, and adipocyte transformation from mesenchymal tissue. The nevocytes are positive with S-100 stain but the lipocytes are negative suggesting that the fat cells in this lesion probably do not from arise from nevocytes. Transformation of mesenchymal element into adipocytes appear to be most likely.
Deba P Sarma, MD, Omaha