Pseudolipomatosis cutis: superficial dermal vacuoles resembling fatty infiltration of the skin.

Empty spaces within the dermis of paraffin-embedded sections of skin have been attributed to fatty infiltration and postulated to originate from topical steroid administration or sebaceous gland rupture. We examined skin biopsy specimens exhibiting dermal vacuolation to determine whether this phenomenon was associated with specific skin diseases and to attempt to illuminate its etiology. Routine hematoxylin-eosin-stained sections from 26 formalin-fixed, paraffin-embedded biopsy specimens were examined. Histochemical stains for mucin and immunohistochemical staining for S100 protein and vascular markers were performed. Dermal vacuolation was characterized by empty spaces, 15-120 microm in diameter, in the superficial dermis, associated with either fibrosis/sclerosis or a lymphocytic infiltrate. There was no relationship to clinical findings, topical steroid treatment, or histologic diagnosis. There was no evidence of true adipocyte differentiation, and vascular markers were negative. Transmission electron microscopy showed nonmembrane-bound irregular spaces in the dermis. Dermal vacuoles likely represent an artifact of tissue fixation or processing and are unrelated to the underlying pathologic process. We propose the name pseudolipomatosis cutis, analogous to insufflation-induced colonic vacuolation, to distinguish this phenomenon from true dermal fatty infiltration and to emphasize its incidental, likely artifactual nature.