Vasculitis-induced membranous fat necrosis.

Membranous fat necrosis (MFN) a distinct degenerative process of adipose tissue, is characterised by the presence of membranocystic lesions (MCLs) superimposed on a background of typical traumatic-type fat necrosis. MCLs are cysts, of varying size and shape, that are lined by an eosinophilic, crenulated membrane, having the staining properties of ceroid. Although MFN has been documented in varying systemic adipose tissue sites and in tumours, the pathogenesis of this pathological curiosity is unknown. To date, an ischemic basis for MFN has been the most proximate, and atherosclerosis and venous insufficiency, due to large and medium vessel disease, have been the most popular underlying clinical disorders. Although systemic vasculitis has been quoted as the underlying ischemic disorder in some patients, vasculitis has not been commented on nor demonstrated in tissue sections in association with MFN. In,reporting vasculitis-induced MFN, we document the occurrence of MFN in association with uncommon causes of vasculitis, namely: 1) Granulomatous vasculitis in a post-herpetic zosteriform scar; 2) Cytomegalovirus-induced vasculitis in the clinical setting of systemic lupus erythematosus; and 3) Lymphocytic vasculitis in a tetanus toxoid immunization site reaction.