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Soft Tissue Tumors
Normal white fat
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Reviewer: David Lucas, M.D., University of Michigan Health Systems (January 2009)
Revised: 26 June 2009, last major update June 2009
Terminology
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● Also called White Adipose Tissue (WAT); cells are called adipocytes
Pathophysiology
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● Main function is energy storage
● Triglycerides circulate in blood in form of chylomicrons; the enzyme lipoprotein lipase, produced by adipocytes and present on luminal surface of endothelium, converts triglycerides to free fatty acids; free fatty acids are taken up by adipocytes and converted to triacylglycerol, which is stored within cytoplasmic lipid droplet of adipocytes
● Adipocytes also secrete leptin and IL6, but their effects in humans are not well defined
● Stromal cells also convert androstenedione to estrone, the main source of estrogen in men and postmenopausal women
Sites
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● Subcutaneous, mediastinum, abdomen, retroperitoneum
Gross description
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● Homogeneous, yellow, greasy surface, faint fibrous septa
Micro description
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● Uniform large spherical cells up to 120 microns, in which lipid droplet pushes nucleus to periphery and deforms it to a thin crescent
● Cytoplasm usually has single, clearly delimited vacuole
● Cells are clear because cytoplasmic fat dissolves during tissue processing
● Nucleus may have central vacuole or Lochkern
● Very thin membranes are present between cells
Micro images
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White adipose tissue and White adipose tissue
vasculature microvessels
Adipocytes along arteriole in mesentery Fat emboli in lung-Oil Red O stain
Virtual slide (Univ Iowa)
Other images: mature adipose tissue with transparent cytoplasm and thin fibrovascular septa #1; #2
Positive stains
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● Vimentin (nonspecific), S100 (primarily for mature adipocytes), calretinin (also stains lipoma and liposarcoma, Hum Path 2006;37:312)
● Oil red O and Sudan Black stain neutral fat (must use frozen tissue because tissue processing removes fat); Oil red O also stains most carcinomas
● Nile blue sulfate stains neutral fat pink-red, and stains fatty acids/phospholipids blue
● Basement membrane is highlighted by PAS and reticulin
Negative stains
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● CD31, keratin, desmin, muscle specific actin
Electron microscopy
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● Pre-adipocytes - spindle cells with abundant endoplasmic reticulum and small spherical mitochondria
● Mature adipocyte - large lipid droplet flattens nucleus against cytoplasmic membrane, variable pinocytotic vesicles; capillaries are close to adipocyte basement membrane
Electron microscopy images
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Subcutaneous adipocytes
End of Soft Tissue Tumors > Normal white fat
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