Neurofibroma

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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Cerofalini E, Landi A, De Santis G, Maiorana A, Canossi G, Romagnoli R: MR of benign peripheral nerve sheath tumors. J Comp Assist Tomog 15:593-7,1991.
Donner TR, Voorhies RM, Kline DG: Neural sheath tumors of major nerves. J Neurosurg 81:362-73,1994.
Enzinger FM, Weiss SW: Benign Tumors of Peripheral Nerves. In Soft Tissue Tumors FM Enzinger and SW Weiss (Eds), C.V. Mosby Co., St. Louis (3rd ed) 1995, pp 821-88.
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Nagey L, McCabe SJ, Wolff TW: A case of neurofibroma of the palmar cutaneous branch of the median nerve. J Hand Surg 15B:489-90,1990.
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