Giant Pigmented Tumor of the Scalp: A Diffuse Neurofibroma or a Congenital Nevus with Neurofibromatous Changes? Immunohistochemical and Electron Microscopic Studies

A 47-year-old woman presented with a giant pigmented tumor on her scalp, characterized by a two-layered structure: an upper non-pigmented portion with neurofibromatous cells and a lower pigmented portion with naevus-like cells. Immunohistochemical analysis showed the presence of S-100 protein and neuron-specific enolase, but not neurofilament or myelin basic protein. Electron microscopy identified melanosomes in the pigmented portion, suggesting a melanocytic origin. However, the absence of superficial pigmentation and associated hair loss contradicted this, indicating the tumor might exemplify dual neural crest differentiation.