Malignant melanoma derived from cerebriform intradermal naevus.

We report a case of malignant melanoma (MM) derived from cerebriform intradermal naevus (CIN) in a 66-year-old Japanese man. The patient had cutis verticis gyrata (CVG) on the posterior area of the scalp at birth. He noticed a dome-shaped nodule at the centre of the CVG at 66 years of age. Histopathological examination found a nodule of MM arising within an extensive area of intradermal naevus. There was no metastasis to lymph nodes or other organs. To our knowledge, only two cases of CIN in which MM had later developed have been reported. We estimated that the incidence of melanoma from CIN including our case is 4.5% (3 of 67 reported cases), which seems to be comparable to the frequency of malignant alteration of giant pigmented naevi. This suggests that pathological examination is recommended for CVG, and once pathological diagnosis of CIN is confirmed, long clinical follow-ups are necessary for detecting development of MM.