Worrisome solitary dark growing nodule on the vertex

Atypical Cellular Blue Nevus (ACBN) is a rare variant of blue nevus with many morphologic features of cellular blue nevus but with some atypical features resembling those of malignant blue nevus. The histological distinction from melanoma may be difficult, even though high mitotic activity, atypical mitotic figures, marked cytologic atypia, cell crowding, expansile growth, and necrosis favour melanoma. Because of the intermediate pathologic features of ACBN, complete excision of the lesion, biopsy of the sentinel lymph node and long-term follow-up of the patient are recommended.