Updated: 6/22/2021

Neurilemmoma

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  •  summary
    • Neurilemmoma, also known as Schwannoma, are benign, encapsulated nerve sheath tumors composed of Schwann cells that occur on the surface of peripheral nerves.
    • The condition usually presents in patients in the 3rd to 6th decades of life with paresthesias in the distribution of the peripheral nerve.
    • Diagnosis is made with biopsy showing a lesion that is well encapsulated in a nerve sheath with histology showing verocay bodies. Immunostaining is positive for S100.
    • Treatment is usually observation for asymptomatic lesions. Marginal resection is recommended in cases of progressive symptoms.
  • Epidemiology
    • Demographics
      • peak incidence is in the 3rd to 6th decades
        • previous test question ages: 40, 45
      • affect males and females equally
    • Anatomic location
      • tumor is well encapsulated on the surface of a peripheral nerve
      • often occurs on flexor surfaces of extremities and head and neck
      • larger lesions may occur in the pelvis
  • Etiology
    • Pathoanatomy
      • can affect motor or sensory nerves
    • Genetics
      • often associated with mutations affecting NF2 gene
    • Malignant transformation
      • extremely rare
  • Presentation
    • Symptoms
      • usually asymptomatic
      • may have paresthesia in the distribution of the peripheral nerve
    • Physical exam
      • may have positive Tinel’s sign in the distribution of the nerve affected may be present
  • Imaging
    • MRI
      • sequences
        • low intensity (dark) T1
        • high intensity (bright) on T2
        • diffuse enhancement with gadolinium
      • findings
        • may show “string sign”
        • difficult to differentiate from neurofibroma
  • Histology
    • Gross pathology
      • the lesion is well encapsulated in a nerve sheath
      • gray in color
    • Histology
      • Antoni A structure
        • a pattern of spindle cells arranged in intersecting bundles (spindle cell battle formation)
      • Antoni B
        • areas with less cellularity with loosely arranged cells
      • Verocay bodies
        • pathognomonic
        • composed of two rows of aligned nuclei in a palisading formation
    • Immunochemistry
      • strongly uniform S100 antibody staining
  • Treatment
    • Nonoperative
      • observation
        • indications
          • asymptomatic lesions
    • Operative
      • marginal excision
        • indications
          • symptoms or interfering with quality of life
        • technique
          • nerve function may be preserved by careful dissection, excising the lesion parallel to the nerve fascicles so the lesion may be extruded.
        • complications
          • small risk of sensory deficits
        • outcomes
          • recurrence is rare

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