Neurosurgery notes/Tumours/Cranial and paraspinal nerve tumours/Hybrid nerve sheath tumour

Hybrid nerve sheath tumour

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Cranial and paraspinal nerve tumours

Definition

  • Essential:
    • Intermingled features of two types of benign nerve sheath tumours AND
      • (i.e. neurofibroma, schwannoma, and perineurioma).
    • Appropriate immunohistochemical staining for each component

Three main combinations

Schwannoma + perineurioma

  • Most common
  • Typically occurs sporadically
  • Predominantly Schwannian cytomorphology but have a perineurioma-like architecture
  • Microscopy
    • 2/3 Schwann cells and 1/3 perineurial cells
    • Well circumscribed
    • Unencapsulated,
    • Composed of spindle cells with plump, tapering nuclei and palely eosinophilic cytoplasm with indistinct cell borders,
    • Cells arranged in a storiform, whorled, and/or lamellar architecture
    • May exhibit myxoid stromal changes (seen in half of all cases) and often display degenerative cytological atypia similar to the ancient changes seen in schwannoma.
  • Immunophenotype
    • Schwannian cells (plump-spindled) being positive for S100 protein
    • Perineurial cells (slender-spindled) show variable immunoreactivity for EMA, claudin-1, and GLUT1

Neurofibroma + schwannoma

  • Associated with
    • Schwannomatosis
    • NF1
    • NF2
  • Microscopy
    • Two distinct components are recognized:
      • Schwannoma like component
        • With nodular Schwann cell proliferation
        • Often with Verocay bodies: nuclear palisading
        • Mainly composed of cellular Antoni A areas,
      • Neurofibroma-like component with a mixed cellular population, myxoid change, and collagen.
        • Plexiform architecture is common
        • Abundant fibroblasts, collagen, and myxoid changes, with Schwannian cells having a distinctive elongated and wavy appearance.
    • Entrapped axons may be seen in neurofibromatosis-associated schwannomas; entrapped large bundles of axons is more common in neurofibromas

Neurofibroma + Perineurioma

  • Rare
  • Usually associated with NF1

Genetic

  • Hybrid neurofibroma/schwannoma
    • A common tumour type in schwannomatosis, occurring in 71% of patients
    • Striking association with neurofibromatosis where the hybrid lesion is more common in NF2 (occurring in 26% of cases) than in NF1 (occurring in 9% of cases).
    • Within patients with schwannomatosis, 61% of the developed tumours had the appearance of schwannoma-like nodules within a neurofibroma-like tumour, corresponding to hybrid neurofibroma/schwannoma
  • Hybrid neurofibroma/perineurioma occurs mostly in association with NF1

Histopathology

Macroscopic

  • gross appearance and radiological findings of hybrid tumours are indistinguishable from those of other PNSTs

Microscopic

Fig. 9.20 Hybrid schwannoma/perineurioma. A Benign spindle cell nerve sheath tumour with loose myxoid stroma that is difficult to classify on H&E alone. B SIOO immunostaining highlights about tN0 thirds of the hybrid nerve sheath tumour cells, identifying the Schwann cell component. C EMA staining highlights about one third of the tumour cells, identifying the perineurial component. Fig. 9.21 Hybrid neurofibroma/schwannoma. Schwann cell micronodules. C S100-positive Schwann cell micronodules.
Hybrid schwannoma/perineurioma. A, Benign spindle cell nerve sheath tumour with loose myxoid stroma that is difficult to classify on H&E alone. B, S100 immunostaining highlights about two thirds of the hybrid nerve sheath tumour cells, identifying the Schwann cell component. C, EMA staining highlights about one third of the tumour cells, identifying the perineurial component.
Fig. 9.20 Hybrid schwannoma/perineurioma. A Benign spindle cell nerve sheath tumour with loose myxoid stroma that is difficult to classify on H&E alone. B SIOO immunostaining highlights about tN0 thirds of the hybrid nerve sheath tumour cells, identifying the Schwann cell component. C EMA staining highlights about one third of the tumour cells, identifying the perineurial component. Fig. 9.21 Hybrid neurofibroma/schwannoma. Schwann cell micronodules. C S100-positive Schwann cell micronodules.
Hybrid neurofibroma/schwannoma. A&B, Schwann cell micronodules. C, S100-positive Schwann cell micronodules.

Localisation

  • Wide anatomical distribution and often involve the dermis and subcutis
    • Are almost exclusively in the digits and extremities
  • Rarely involving cranial or spinal nerves.

Clinic features

  • Largely depend on the site of origin.
  • Cause neurological deficit or pain when they involve a large peripheral nerve