Neurosurgery notes/Tumours/Cranial and paraspinal nerve tumours/Malignant melanotic nerve sheath tumour

Malignant melanotic nerve sheath tumour

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Cranial and paraspinal nerve tumours

General

  • Aka
    • Malignant melanotic Schwannian tumour
  • Should not use terminology
    • Melanotic schwannoma
      • Previously named
    • Psammomatous melanotic schwannoma.

Definition

  • Essential:
    • Fascicular to sheet-like proliferation of variably pigmented, relatively uniform, plump, spindled to epithelioid cells AND
      • Coexpression of S100/SOX10 and melanocytic markers (e.g. HMB45, melan-A)
        • OR
      • Loss of PRKAR1A expression, or PRKAR1A mutation
    • AND (for unresolved lesions)
      • Methylation profile of malignant melanotic nerve sheath tumour
  • Desirable:
    • Origin from a paraspinal or visceral autonomic nerve

Localization

  • Spinal or autonomic nerves near the midline
    • Most common
  • Rare
    • GI tract, bone, soft tissues, heart, bronchus, liver, and skin

Pathology

  • Macroscopic
      • Sporadic MMNSTs are solitary
      • Carney complex: multiple and multicentric tumours
      • Circumscribed or partially encapsulated, and they are frequently heavily pigmented, with the appearance of dried tar
       
      Malignant melanotic nerve sheath tumour. Tumour arising in a spinal nerve root. The tumour is heavily pigmented and partially encapsulated.
      Malignant melanotic nerve sheath tumour. Tumour arising in a spinal nerve root. The tumour is heavily pigmented and partially encapsulated.
  • Microscopic
      • Fig. 9.10 Melanotic schwannoma with clusters of plump, spindled, and epithelioid, heavily pigmented tumour cells.
      Melanotic schwannoma with clusters of plump, spindled, and epithelioid, heavily pigmented tumour cells.
      A close-up of a microscope AI-generated content may be incorrect.
      Malignant melanotic nerve sheath tumour. A, Cellular detail is obscured by heavy pigment deposition. B, Sheets of vaguely syncytial epithelioid cells. C, Tumour cell-specific loss of PRKAR1A expression (immunohistochemistry for PRKAR1A with red chromogen).
    • Psammoma bodies are present in roughly 50% of cases
    • MMNSTs strongly express S100 and SOX10, as well as various melanocytic markers, including HMB45, melan-A, and tyrosinase.

Genetics

Clinical features

  • Pain
  • Sensory abnormalities
  • Mass effect
  • Bone erosion
  • Systemic symptoms
    • May be seen in patients with metastatic disease.
    • Eg
      • Respiratory failure
      • Liver failure
  • Although it was once thought that psammoma bodies were more likely in familial tumours, there are no clinical differences between psammomatous and non-psammomatous MMNSTs, with both showing a variable association with Carney complex, loss of PRKAR1A expression, and similar clinical behaviour

Prognosis

  • 53% of patients followed for > 5 years have been reported to have remained disease-free