Juvenile xanthogranuloma: a congenital giant form leading to a wide atrophic sequela.

Juvenile xanthogranuloma is the most common non-Langerhans cell histiocytosis of infancy and childhood. It is a benign disorder that usually regresses spontaneously, more often without or with limited skin changes. The clinical features are very pleomorphic and recognition of the atypical presentations should facilitate the diagnosis. We report a 9-month-old boy who had an extensive, atrophic lesion on the proximal thigh that followed the course of the congenital giant form. The large size of the lesion does not alter the clinical course or result in extracutaneous involvement, which remains rare. However, uncommon clinical presentations raise the problem of differential diagnosis, requiring biopsy to eliminate other tumors with a less favorable prognosis.