Neurosurgery notes/Tumours/Melanocytic tumours

Melanocytic tumours

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Diffuse meningeal melanocytic neoplasms: Melanocytosis and melanomatosis
Circumscribed meningeal melanocytic neoplasms: Melanocytoma and melanoma

Consist of

Definition

  • Primary melanocytic neoplasms of the CNS are diffuse or localized tumours that presumably arise from leptomeningeal melanocytes.
  • Melanocytosis
    • Benign lesions that are diffuse without forming macroscopic masses
    • Localized to meninges only
  • Melanomatosis:
    • Malignant (not actually malignant, it only can invade into CNS parenchyma) diffuse or multifocal lesions
  • Melanosis
    • Melanocytosis + Melanomatosis
  • Melanocytoma
    • Benign or intermediate grade tumoural lesions
  • Melanomas
    • Malignant lesions that are discrete tumours
Types
Melanocytosis
Melanomatosis
Melanocytoma
Melanomas
Aggressiveness
Benign
Benign
Benign
Malignant
Localized/diffuse
Diffuse
Diffuse
Localized
Localized
Parenchymal invasion
No
Yes
No
Yes
Nuclear atypia
No
No
No
Yes

Histopathology

Microscopy

  • Diagnosis based on melanocytic differentiation.
    • Histologically
    • CSF cytology
  • Most display melanin pigment within the
    • Tumour cytoplasm
    • Tumour stroma
    • Tumoural macrophages cytoplasm (melanophages).
  • Rare melanocytomas and occasional primary melanomas do not demonstrate melanin pigment
  • Ki-67 index
    • < 1-2% in melanocytomas
    • 8% in primary melanomas

Immunophenotype

  • Positive
    • Always
      • Anti-melanosomal antibodies HMB45
      • Melan-A
      • Microphthalmia-associated transcription factor (MITF)
    • Variable
      • S100 protein
      • Vimentin
      • Neuron-specific enolase
    • Rare
      • GFAP
      • NFPs
      • Cytokeratins
      • EMA
  • Within blood vessels and larger tumoural nests but not within the tumour itself
    • Collagen IV
    • Reticulin

Cell of origin

  • Normal CNS
    • Melanocytes localized at
      • Base of the brain
        • Along ventral medulla oblongata
      • Along upper cervical spinal cord.
  • Leptomeningeal melanocytes derived
    • From the neural crest
    • These melanocytes may differ developmentally from melanocytes in epithelia (e.g. the epidermis and mucosal membrane) and seem to be more closely related to melanocytes in the uveal tract.
  • Melanocytic neoplasms associated with neurocutaneous melanosis derive from melanocyte precursor cells that reach the CNS after acquiring somatic mutations, mostly of NRAS.

Imaging

  • Hyperintensity at T1 seals the diagnosis but the intensity depends on the level of melanin

Differential diagnosis

  • Other melanotic tumours that involve the CNS
    • Metastatic melanoma
    • Primary tumours undergoing melanization
      • Melanotic schwannoma
      • Medulloblastoma
      • Paraganglioma
      • Various gliomas
      • Melanotic neuroectodermal tumour of infancy (retinal anlage tumour)
        • Intracranial locations

Management

  • Pellerino (EURACAN) 2024 
    • Management of circumscribed meningeal melanoma should follow high‑grade CNS melanoma principles:
      • Maximal safe resection
      • Staging to exclude extracranial disease
      • Multidisciplinary planning for radiotherapy and systemic therapy.
    • If gross total resection is not possible due to localisation or the extent of the tumor, an open or stereotactic biopsy should be performed to achieve integrated diagnosis
    • Systemic therapies
      • Should be considered in the case of residual/progressive disease of meningeal melanocytoma/melanoma, when surgery and/or radiotherapy have been exhausted, or in patients with primary diffuse leptomeningeal melanocytosis or melanomatosis.
    • RT
      • High-dose radiotherapy is rarely indicated in diffuse melanocytic tumors except as palliative treatment to alleviate symptoms if appropriate
      • After subtotal resection and should be considered in localized malignant melanoma even after gross-total resection,