Membranous fat necrosis.

We report the case of a 66-year-old man with nodular lesions on the chest that were clinically diagnosed as epidermal cysts. Histologically the lesions consisted of fat necrosis with cystic spaces lined by striking membranous structures, mimicking a parasitic cuticle and exhibiting all the staining reactions of ceroid. Retrospective review of 33 consecutive cases of fat necrosis revealed similar membranous changes in 21% of the cases. The etiology and pathogenesis of this variant of fat necrosis are uncertain.