Lipomembranous (Membranocystic) Fat Necrosis

Clinicopathologic correlation of cutaneous biopsy specimens demonstrating typical lipomembranous fat necrosis was performed. Material from 732 biopsies of various subcutaneous inflammatory disorders seen at our institution in the past 5 years was screened for typical lipomembranous (membranocystic) changes in the panniculus, and 39 specimens from 38 patients with these changes were identified. The most common clinical context in which this condition was observed was in chronic sclerotic plaques of the lower legs associated with venous insufficiency (37% of the total cases). All patients were women, and the majority were obese. Typical lipomembranous fat necrosis was also observed in eight cases (21%) of erythema nodosum, three (8%) of morphea or subcutaneous morphea (or both), two (5%) of lupus panniculitis, two (5%) of necrobiosis lipoidica, and in single cases of polyarteritis nodosa, necrotizing vasculitis, and erysipelas. Six cases (16%) had no definite underlying disease. The mean age of all patients was 57 years (range 32-86 years), and 34 patients (89%) were women. Of the five major categories identified, lipomembranes lining macrocysts and microcysts were most prominent in the venous insufficiency- and morphea-related cases and were much less prominent in erythema nodosum, lupus panniculitis, and necrobiosis lipoidica, which generally showed histopathologic findings typical of these disorders. In addition to lining the macrocystic and microcystic cavities formed in the fat lobules, lipomembranes were prominent in areas of septal fibrosis in all cases associated with morphea and necrobiosis lipoidica and in 35% and 25% of venous insufficiency- and erythema nodosum-related cases, respectively. In lupus panniculitis, lipomembranes were most prominent in areas of hyaline necrosis. We conclude that lipomembranous fat necrosis is most likely a nonspecific form of ischemic fat degeneration that may be induced by various clinical entities. This change is most often seen in venous insufficiency-associated chronic sclerotic plaques typically observed in middle-aged obese women, and we propose the term stasis-associated lipomembranous panniculitis (SALP) to describe this most common form of lipomembranous fat necrosis.