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Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other
Neurofibroma
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Revised: 14 March 2010, last major update July 2009
Variants: dendritic cell with pseudorosettes, Diffuse cutaneous, Focal cutaneous, Intraneural, Pacinian, pigmented (melanotic), Plexiform
Definition
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● Solitary tumor suggests patient does NOT have neurofibromatosis type 1
● Malignant transformation rare in sporadic neurofibromas
Gross description
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● Not encapsulated, softer (more gelatinous) than schwannoma
● Superficial tumors are small, pedunculated nodules protruding from skin (molluscum pendulum)
● Deeper tumors are larger, may cause tortuous enlargement of peripheral nerves (plexiform neurofibromas)
Micro description
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● Non-encapsulated
● Proliferation of all elements of peripheral nerves
● Schwann cells with wire like collagen fibrils (wavy serpentine nuclei, pointed ends), stromal mucosubstances, mast cells, Wagner-Meissner corpuscles, Pacinian corpuscles, axons (highlight with silver or acetylcholinesterase stain, NSE, neurofilament), fibroblasts and collagen
● Perineurial cells in plexiform types, mitotic figures are rare
● May be infiltrative
● Less of a fascicular pattern than fibromatosis
● May have myxoid areas
● No Verocay bodies, no nuclear palisading, no hyalinized thickening of vessel walls
● Rarely has skeletal differentiation (neuromuscular hamartoma)
Micro images
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Low power
High power
Positive stains
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● S100
● CD34+ (focal)
● Factor 13a (focal)
Negative stains
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● EMA (except in plexiform neurofibromas)
Electron microscopy
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● Schwann cells enclose axons in plasmalemmal invaginations (mesaxons)
Differential Diagnosis (myxoid areas)
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● Myxoma
● Myxoid liposarcoma
Diffuse cutaneous neurofibroma
Definition
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● Traps adnexa, infiltrates into fat
Differential Diagnosis
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● Blue nevi
● Melanoma
Definition
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● Twisted, complex, large if deep
● May be too big to resect
● 5% transform to MPNST, higher rate than classic neurofibromas, usually large tumors attached to major nerve trunks in neck or extremities
Sites
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● Orbit
● Neck
● Back
● Inguinal
Positive stains
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● EMA (perineurial cells, not in ordinary neurofibromas)
End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Neurofibroma
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