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Soft Tissue Tumors
Normal brown 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 Brown Adipose Tissue (BAT)
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
Sites
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● More conspicuous in infants (5% of body weight, diagram) 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)
Epidemiology
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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 (Archives 1992;116:1152); also Duchenne’s muscular dystrophy (Archives 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
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 Multivacuolated cytoplasm
Multivacuolated cytoplasm CD31 (figures 1-3)
Positive stains
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● CD31 (Archives 2006;130:480)
● Also mitochondrial membrane uncoupling protein (J Histochem Cytochem 1993;41:759)
Electron microscopy
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● Numerous mitochondria
Additional references
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End of Soft Tissue Tumors > Normal brown fat
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