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Soft Tissue Tumors
Lipomatosis of nerve
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Reviewer: David Lucas, M.D., University of Michigan Health Systems (January 2009)
Revised: 4 October 2009, last major update June 2009
Definition
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● Infiltration of epineurium of a major nerve by adipose and fibrous tissue
Terminology
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● Also called fibrolipoma of nerve, fibrolipomatous hamartoma of nerve, macrodystrophia lipomatosa
Epidemiology
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● May be noted at birth
● Almost always age 30 years or less
● Associated with macrodactyly (abnormal enlargement of digits) innervated by affected nerve in 30-67%
Sites
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● 85% of patients have involvement of median nerve and its digital branches in hand, wrist and forearm (Histopathology 1994;24:391)
● Also ulnar nerve
Radiology
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● T1 weighted images on MR imaging reveal a fatty mass that is evenly distributed between nerve bundles and is seen running along individual nerves
● Often described as having a “coaxial cable-like” appearance on axial scans (Acta Radiol 2003;44:326)
Case reports
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● 26 year old man with sciatic nerve involvement (Microsurgery 2009;29:66)
● 26 year old man with mass on palm of hand (Case of Week #158)
● Bilateral case (Muscle Nerve 1998;21:656)
Treatment and prognosis
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● Benign condition, but often no effective treatment as resection causes sensory and motor deficits (J Neurosurg 1998;89:683)
● Carpal tunnel release may relieve symptoms of median nerve involvement
● Amputation if severe deformity
● May recur in 33-60% if incomplete resection
Clinical images
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Lipomatosis of median Thickened median nerve
nerve with macrodactyly
Thickened median nerve
Gross description
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● Fusiform enlargement of nerve by yellow adipose tissue, confined within epineurium
Gross images
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Excised tissue with macrodactyly
Micro description
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● Infiltration of epineurium and perineurium by adipose and fibrous tissue (collagen), causing enlargement of nerve
● Concentric perineurial fibrous tissue and pseudo-onion bulb formation
● Occasionally metaplastic bone
Micro images
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Tumor of second digit With osseous and soft-tissue
hypertrophy and predominance of fat
Lipomatous infiltration around Lipomatous infiltration around
nerve fascicles #1 nerve fascicles #2
Case of Week #158
Differential Diagnoses
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● Intraneural lipoma - fatty tissue displaces nerve bundles, but does not separate them
● Diffuse lipomatosis - not confined to the epineurium.
● Traumatic neuroma - has onion bulb formation, but usually lacks concentric perineural fibrosis, and has a high T2 signal density on magnetic resonance imaging
Differential Diagnoses of macrodactyly
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● Angiomatosis
● Neurofibromatosis type 1
● Klippel-Trenaunay-Weber syndrome (eMedicine)
● Proteus syndrome (Wikipedia)
End of Soft Tissue Tumors > Lipomatosis of nerve
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