DEFINITION AND PATHOGENESIS

  • Solitary lesion (90%) or occurring in von Recklinghausen’s disease (10%) of Schwann cells
  • Types
  • Storiform perineural fibroma
  • Pacinian neurofibroma
  • Epithelioid neurofibroma
  • Pigmented neurofibroma —melanocytic differentiation (both Schwann cells and melanocyte of neural crest origin)

IMPORTANCE

  • Large lesions (>4cm) may not be benign and require resection after workup
  • Commonly associated with neurofibromatosis
  • ~5% of benign soft tissue tumors

CLINICAL FEATURES

  • M=F to slight M preponderance reported
  • Most patients 20-30 years of age
  • Most superficial dermal or subcutaneous lesions
  • Solitary spinal neurofibroma may present with radicular sxs
  • Has been reported occurring in the same nerve trunk as a neurilemoma

RADIOLOGIC FEATURES

  • MRI best demonstrates ovoid lesion that is well circumscribed
  • Spinal lesion x-ray may show pedicle or vertebral body erosion, ? interpedicular distance, laminae(e) distortion, neural foramenal enlargement
  • Myelography: "amputation" of nerve root with a filling defect
  • US: well-defined hypoechoic lesion
  • CT: intra- and extraspinal "hour-glass" appearance
    • Hypodense to muscle
    • Enhances with contrast
  • MRI:
    • T1-weighted images show intensity of lesion slightly higher than muscle
    • T2-weighted images show signal (peripheral > central) with bright non-uniform gadolinium DPTA enhancement (peripheral > central)("target sign")

GROSS PATHOLOGY

  • Grayish-white to yellow-brown
  • Not encapsulated (unlike neurilemmoma)
  • May be myxomatous to hard and rubbery

HISTOLOGIC FEATURES

  • Lack two distinct zones (unlike neurilemmoma)
  • Interlacing elongated cell bundles with wavy nuclei of varying cellularity
  • Arrangement of cells in fascicles, whorls, or storiform
  • EM
    • Schwann cells with a large nuclei, little cytoplasm, and pronounced basal lamina
    • Fibroblast-like cells and mast cells also are present

DIFFERENTIAL CLINICOPATHOLOGIC DIAGNOSIS

  • Myxoma
  • Neurilemoma (S-100 usually negative, unlike neurilemoma)

DISEASE COURSE AND TREATMENT

  • Simple excision
  • Residual numbness should be warned about, esp in digital locations (where grafting may be appropriate)
  • Risk of malignant degeneration small, esp in solitary lesions

SPECIAL CONSIDERATION

  • NEUROTHEKEOMA

    • (Nerve sheath myxoma)
    • Involve head, neck, and shoulder, arising in childhood
    • Usually superficial
    • Lobular areas of myxoid material with neural cell differentiation demonstrated by EM

REFERENCES

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