Pseudo-tumoral proliferative nodule in a giant congenital nævus

Objective: To discuss the characteristics of proliferative nodules in giant congenital nævi. Methods: We report the case of a newborn referred for staged curettage of a giant congenital nævus. A nodule was discovered on his left flank. It was excised for analysis during the first treatment session during the second week of life. Results: The nodule was soft and looked like a lipoma. On optical microscopy however, there was a high cellular density and a high number of mitoses. Although the genetic analysis for melanoma antigens was reassuring, a firm nodule recurred a few days later. A second excision was performed at the fourth week. Surprisingly, on optical microscopy, the cellular density was much lower and there were no more atypias or mitoses; many neurotization foci were present. The natural history changed to spontaneous regression of the cellular activity. The diagnosis of proliferative nodule was made. Conclusion: Proliferative nodules in giant congenital nævi have specific clinical and histological characteristics. These should however be put into perspective. As demonstrated in this case, there can be an initial high mitotic activity within the nodule but this should not lead to the misdiagnosis of malignant melanoma. The spontaneous regression of cellular activity will allow the correct diagnosis to be made.