Soft Tissue Tumors - Normal brown fat

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Soft Tissue Tumors

Adipose tissue

Normal brown 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 Brown Adipose Tissue (BAT)

Sites
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● More conspicuous in infants (5% of body weight) and children; replaced with white fat over time
● Persists in adults in interscapular region, neck, mediastinum, axilla, retroperitoneum (perirenal) (diagram)
● Substantial amounts of metabolically active brown fat are present in healthy adults (N Engl J Med 2009;360:1518)

Pathophysiology
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● Main function is heat production (nonshivering thermogenesis), mediated through a dense vascular system and sympathetic nerves (Physiol Rev 2004;84:277)
● Brown fat mitochondria express uncoupling protein (UCP1), which uncouples fatty oxidation from ATP generation, which causes energy to be dissipated as heat
● Cold exposure leads to sympathetic stimulation of brown fat via norepinephrine binding to beta adrenergic receptors, then oxidation of fatty acids and heat production
● Protein-tyrosine phosphatase 1B is a modulator of brown fat adipogenesis (PLoS One 2011;6:e16446)
● Moderate intermittent stress can stimulate brown adipose tissue growth and thermogenic activity

Clinical features
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● Increased presence is associated with alcohol abuse, malnourishment and cachexia (may maintain body temperature in those with diminished subcutaneous fat), cardiovascular disease (Arch Pathol Lab Med 1992;116:1152); also Duchenne’s muscular dystrophy (Arch Pathol Lab Med 1988;112:550)
● Brown fat thermogenesis is visible with a thermal (infrared) camera in infants over neck and interscapular area
● Also important in animals coming out of hibernation, allowing them to rewarm quickly

Diagrams
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Sites of brown fat

Gross description
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● Red-brown (less lipid) to tan (more lipid) due to vascularity and numerous mitochondria
● Has glandular and lobular appearance

Micro description
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● Lobules of adipocytes, capillaries, nerves and connective tissue
● Adipocytes are smaller (25-40 microns) than in white fat, are polygonal with acidophilic multivacuolated and granular cytoplasm and central spherical nucleus with fine indentations

Micro images
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Multivacuolated cytoplasm

CD31

Positive stains
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● CD31 (Arch Pathol Lab Med 2006;130:480)
● Also mitochondrial membrane uncoupling protein (J Histochem Cytochem 1993;41:759)

Electron microscopy description
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● Numerous mitochondria and smaller amounts of lipid droplets

Additional references
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● Wikipedia, J Mol Cell Biol 2010;2:23

End of Soft Tissue Tumors > Adipose tissue > Normal brown fat

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