An unusual presentation of a vascular birthmark: a focal area of congenital lipoatrophy on the buttock.

A 3-year-old girl presented with a focal area of congenital lipoatrophy on the buttock. There was no history of trauma or injections to the site. An excisional biopsy of the lesion was performed. The pathology of the lesion was most consistent with a vascular malformation with capillary predominance. This is an unusual presentation of a capillary malformation that has not been reported in the literature. The normal clinical presentation, natural history, pathologic findings, and imaging findings of capillary malformations are reviewed. These characteristics are compared to other easily confused lesions, such as haemangiomas, including infantile, rapidly-involuting, and non-involuting haemangiomas. Usually, the clinical appearance of congenital vascular lesions confers the ability to correctly distinguish these birthmarks. However, as this case demonstrates, the possibility of a vascular lesion should be considered with any congenital cutaneous lesion regardless of its appearance.