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PH-NE09

Meningeal and peripheral nerve tumours

How arachnoid and Schwann cells give rise to meningiomas, schwannomas and neurofibromas, why these mostly benign tumours harm by compressing brain, cord and nerves, and how NF1 and NF2 predispose to them and to malignant nerve sheath tumours.

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  • 5 steps · 10 questions
  • 3D normal anatomy

By the end, you can

  • Relate the meninges and the sheaths of peripheral nerves to the cells that give rise to meningiomas, schwannomas and neurofibromas.
  • Describe the gross and microscopic appearance of meningioma, schwannoma and neurofibroma, including whorls, psammoma bodies, Antoni A and B areas and Verocay bodies.
  • Explain how loss of merlin (NF2) and neurofibromin (NF1) leads to tumours, and why each syndrome predisposes to different ones.
  • Explain why benign extra-axial tumours cause symptoms by compression, using vestibular schwannoma and meningioma as examples.
  • Describe how meningiomas are graded and how a malignant peripheral nerve sheath tumour arises and behaves.
  • Recognise the classic appearances, grading systems (WHO grade, Simpson, Koos) and tests such as MRI of the internal acoustic canal and audiometry, and explain how surgery, stereotactic radiosurgery and drugs targeting the NF pathways act.

What it is

Meningiomas arise from the meningothelial (arachnoid cap) cells of the arachnoid and grow attached to the dura. Nerve sheath tumours arise from the cells round cranial and peripheral nerves: schwannomas from Schwann cells, neurofibromas from a mixture of Schwann cells, fibroblasts and perineurial-like cells, and the malignant peripheral nerve sheath tumour (MPNST), a sarcoma. Most lie outside the brain and cord (extra-axial) and are benign, harming by compression.

4 types to tell apart
Meningioma
The commonest primary tumour inside the skull; dural-based; CNS WHO grade 1, 2 (atypical) or 3 (anaplastic).
Schwannoma
Encapsulated tumour of Schwann cells that pushes the parent nerve aside; vestibular schwannoma is the commonest intracranial one; linked to NF2.
Neurofibroma
Unencapsulated tumour with axons running through it; cutaneous or plexiform; plexiform neurofibromas are characteristic of NF1.
Malignant peripheral nerve sheath tumour
A high-grade sarcoma, about half in people with NF1, often arising in a plexiform neurofibroma.

US spelling: tumours → tumors, tumour → tumor, fibres → fibers.

Normal function

The meninges and the sheaths of nerves

Three membranes cover the brain and spinal cord: the tough against the , the thin and the delicate pia on the brain surface. Clusters of arachnoid cap cells (meningothelial cells) sit in the arachnoid granulations that bulge into the dural venous sinuses such as the , where CSF drains into the blood.

Cranial and peripheral nerves, beyond a short stretch where the central nervous system ends, are wrapped by Schwann cells: each myelinating Schwann cell covers one segment of one axon. Fibroblasts lie between the fibres in the endoneurium, perineurial cells wrap each bundle, and the epineurium binds the whole nerve.

These coverings lie outside the brain and cord substance, so their tumours are extra-axial: they push brain, cord and nerves aside rather than infiltrating them. Many are benign, yet in a confined space even a slow, benign tumour can cause serious damage.

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