S10C8P6-Membranous Lipodystrophy

S10C8P6-1: This is the pattern of “membranous lipodystrophy.” In this reaction to injury, a convoluted membrane forms along the internal surface of rounded, lipid-filled defects. The defects vary in size; they do not represent viable (nucleated) lipocytes. They are related to that form of death of adipose tissue in which rounded defects with distinct walls are generally regularly spaced and often back to back in the pattern of normal lipocytes. In contrast to viable fat, the rounded defects are not representative of viable cells (there are no eccentric nuclei). In addition, the defects vary in size; many tend to be larger than viable lipocytes. The defects are filled with lipids that are liberated following the death of lipocytes. A few clusters of histiocytes are present among the defects. This pattern of membranous lipodystrophy is a non-specific response of adipose tissue to injury, particularly vascular insults. The membrane probably is of histiocytic origin.

S10C8P6-2: This is a colorful example of an area of panniculitis showing membranous lipodystrophy (from near the center of the field and up). There is a zone of fibrinoid change below the center of the field. To the left near the margin of the field, there is a yellow pigment compatible with hematoidin. To the left and below the fibrinoid material, clear, “lipid-filled” vacuoles are closely spaced; they vary in size. Eccentric nuclei are not associated with the vacuoles.

S10C8P6-3: To the right, some of the vacuoles show the lipomembranous change. To the left, infiltrates of histiocytes are diffuse. There are vacuoles which vary in size among the histiocytes (a lipogranulomatous pattern). Some of the histiocytes have vacuolated cytoplasm (xanthogranulomatous change - lipogranulomatous reaction).

S10C8P6-4: At higher magnification, there are lipogranulomatous (xanthogranulomatous) features. Many of the histiocytes have vacuolated cytoplasm (i.e., lipophages with multiple vacuoles that vary in size). The larger, solitary vacuoles in this area probably represent a variant expression of lipid-rich histiocytes (lipophages); some of the vacuoles indent an eccentric nucleus.

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