Soft Tissue Tumors - Normal white fat

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Soft Tissue Tumors

Adipose tissue

Normal white fat

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 30 October 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

Terminology
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● Also called White Adipose Tissue (WAT)
● Cells are called adipocytes

Sites
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● Subcutaneous, mediastinum, abdomen, retroperitoneum

Pathophysiology
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● Main function is energy storage as lipid, which is mobilized to other tissues depending on metabolic needs
● Triglycerides circulate in blood as 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

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; 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 vasculature

Adipocytes along arteriole in mesentery O stain

White adipose tissue

Fat emboli in lung-Oil Red O stain

● Other images: mature adipose tissue #1; #2

Virtual slides
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Fat (adipose tissue)

Positive stains
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● Vimentin (nonspecific), S100 (primarily for mature adipocytes), calretinin (also stains lipoma and liposarcoma, Hum Pathol 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 description
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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 > Adipose tissue > Normal white fat

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