S10C11P9-Fat Necrosis of Newborn

S10C11P9-1: The infiltrates are lobular. In the lobule to the left, the infiltrates are diffuse; they are prominently histiocytic and have granulomatous qualities. There are scattered, rounded vacuoles among the histiocytes. The vacuoles vary in size; most are larger than the lipocytes in the more normal fat to the right at the bottom of the field (fat necrosis of the newborn).

S10C11P9-2: At a higher magnification, a distinctive change is a prominent feature. Histiocytes and giant cells are arranged radially at the periphery of angulated defects. The cytoplasm of histiocytes extends among the angulated clefts; the cytoplasmic extensions are pale. The clefts are sites in which lipid crystals have been removed during the processing of the biopsy specimen. The solvents used to remove lipids from tissue, in preparation for paraffin impregnation, also dissolve the crystals in the centers of the distinctive granulomas (fat necrosis of the newborn).

S10C11P9-3: The distinctive granulomas are seen at higher magnification. To the right below the center of the field, there is a mitotic figure in a histiocyte.

S10C11P9-4: The reticulated cytoplasm and the angulated defects are adaptations for lipid crystals; the crystals formed in the tissue in response to damaged fat, but were dissolved during processing of the tissue.

S10C11P9-5: The radially arranged cells are both individual histiocytes and multinucleated histiocytic giant cells.

S10C11P9-6: In this field, it would appear that newly recruited histiocytes (blue arrows) have joined the population of cells investing the crystals; the “newly recruited cells have distinct cell membranes.

 

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