• Benign nonneoplastic overgrowth of nerve fibers and Schwann cells
• Usually post-traumatic; proximal nerve regenerates into a tangled mass of nerve fibers if it does not meet the distal end
• Painful

• 43 year old woman with post-mastectomy mass (World J Surg Oncol 2012;10:35)

• Axons, Schwann cells, perineurial fibroblasts, also scar

Post-mastectomy

• CD68 (Schwann cells-become phagocytic)

• Tumor-like secondary hyperplasia that develops post-partial/total amputation

• 60 year old patient post-cholecystectomy (Gastroenterol Clin Biol 2005;29:79)
• 70 year old man post-cholecystectomy and choledochojejunostomy (Korean J Gastroenterol 2008;52:32)

After neck surgery

L: S100, R: EMA

• 2 lesions in mastectomy scars with features of both granular cell tumor and traumatic neuroma (Arch Pathol Lab Med 2000;124:709)

• Nests of large granular cells, in background of fibrous tissue with sparse inflammatory infiltrates
• May have tortuous hypertrophic nerve bundles in fibrous tissue, some with degenerative changes and containing granular cells

Large granular cells in dense collagenous stroma

• S100, NSE, vimentin, CD68

• Also called Morton’s metatarsalgia
• More common in adult women
• Due to repeated mild trauma to interdigital plantar nerve, usually between toes 3 and 4

Metatarsal heads, intermetatarsal ligament, neuroma

• Affected nerve is markedly distorted

Neuroma, fibrofatty tissue

• Extensive concentric perineurial fibrosis, thickened arterioles with thrombi

• Also called solitary circumscribed neuroma
• Small, solitary, asymptomatic skin papule, in face of middle-aged

• Dermal lesion with proliferation of Schwann cells (S100+) and axons (neurofilament+), encapsulated by perineurium (EMA+)

Various images

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