• Benign, common, spindle cell tumor; multiple tumors associated with neurofibromatosis type 1
• Solitary tumor suggests patient does NOT have neurofibromatosis type 1
• Malignant transformation rare in sporadic neurofibromas

• 19 year old man with abdominal wall tumor (Biomedica 2009;29:501)
• 51 year old woman with floor of mouth tumor (Case Report Otolaryngol 2011;2011:967896)
• 52 year old man with scrotal mass (Urol Ann 2012;4:119)

• Plexiform neurofibroma: irregularly expanded nerve bundles with nodular appearance, prominent myxoid matrix; associated with NF1
• Diffuse cutaneous: traps adnexa, infiltrates into fat
• Focal cutaneous
• Intraneural

Mouth

Skin

• 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)

Scrotal tumor

• 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
• Less of a fascicular pattern than fibromatosis
• May be infiltrative, have myxoid areas, contain melanin pigment, have epitheloid morphology
• Rarely has skeletal differentiation (neuromuscular hamartoma)
• No Verocay bodies, no nuclear palisading, no hyalinized thickening of vessel walls

Various images

Abdomen

Mouth

• S100, CD34+ (focal), Factor 13a (focal)

• EMA (except in plexiform neurofibromas)

• Schwann cells enclose axons in plasmalemmal invaginations (mesaxons)

• Myxoid liposarcoma
• Myxoma

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