Soft Tissue Tumors - Lipomatosis of nerve

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Soft Tissue Tumors

Adipose tissue

Lipomatosis of nerve

Reviewer: Charanjeet Singh, M.D. (see Reviewerspage)
Revised: 11 November 2012, last major update June 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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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% 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 the Week #158)
● 32 year old woman (J Orthop Surg (Hong Kong) 2011;19:123)
● 46 year old man with bilateral involvement (Muscle Nerve 1998;21:656)

Treatment and prognosis
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● Benign 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

Gross description
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● Fusiform enlargement of nerve by yellow adipose tissue, confined within epineurium

Clinical images
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Lipomatosis of median nerve with macrodactyly

Thickened median nerve

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 nerve fascicles

Case of the Week #158

Lipoma of nerve

Differential diagnosis
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● Intraneural lipoma: mass of fatty tissue displaces nerve bundles, but does not separate them
● Diffuse lipomatosis: not confined to epineurium
● Traumatic neuroma: onion bulb formation, usually lacks concentric perineural fibrosis, has high T2 signal density on magnetic resonance imaging

Differential diagnosis of macrodactyly
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● Angiomatosis
● Neurofibromatosis type 1
● Klippel-Trenaunay-Weber syndrome (eMedicine)
● Proteus syndrome (Wikipedia)

End of Soft Tissue Tumors > Adipose tissue > Lipomatosis of nerve

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