CNS & pituitary tumors


Arachnoid cyst

Last author update: 1 February 2012
Last staff update: 9 March 2023 (update in progress)

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PubMed Search: CNS arachnoid cyst

Eman Abdelzaher, M.D., Ph.D.
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Cite this page: Abdelzaher E. Arachnoid cyst. website. Accessed March 22nd, 2023.
Definition / general
  • Benign subarachnoid accumulation of CSF of congenital origin (Rev Neurol 2004;39:1161)
  • 1% of intracranial masses
  • Arachnoid cysts may be discovered in utero (by ultrasound screening) or be discovered during childhood or adulthood
  • Arise within both cranial and spinal meninges
  • Expand at expense of brain or spinal cord
  • Favored intracranial sites include middle fossa near temporal lobe and cerebellopontine angle
  • Congenital lesions that arise from reduplication or splitting of leptomeninges
  • Sporadic or associated with other malformations or diseases
Clinical features
  • Depends on size and location
  • Symptoms more common in middle fossa cysts; include headache and seizures
Radiology description
  • MRI distinguishes between CSF contents and lipid rich contents of epidermoid and dermoid cysts
Radiology images

Images hosted on other servers:

MR: arachnoid cyst

Various images

Case reports
  • Surgery if symptomatic
Gross description
  • Variable size but may be vary large
  • Thin transparent wall with clear, colorless fluid
  • Cyst is distinct from leptomeninges and dura
Microscopic (histologic) description
  • Cyst wall formed of delicate fibrous connective tissue lined by meningothelial cells (diffuse or focal)
Positive stains
  • Meningothelial cells are positive for EMA
Negative stains
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