CNS & pituitary tumors

Cysts

Arachnoid cyst


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Deputy Editor-in-Chief: Chunyu Cai, M.D., Ph.D.
Saman Seyed Ahmadian, M.D.

Last author update: 25 May 2023
Last staff update: 6 October 2023

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PubMed Search: CNS arachnoid cyst

Saman Seyed Ahmadian, M.D.
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Cite this page: Ahmadian SS. Arachnoid cyst. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumorarachnoidcyst.html. Accessed March 28th, 2024.
Definition / general
Essential features
  • Nonneoplastic, intracranial CSF filled spaces lined by meningothelial cells and an outer collagenous membrane
  • Most primary developmental arachnoid cysts occur in the middle frontal fossa due to the splitting of arachnoid membranes (J Neuropathol Exp Neurol 1981;40:61)
  • Meningothelial cells are positive for epithelial membrane antigen (EMA)
Terminology
  • Meningeal cyst
ICD coding
  • ICD-10: G93.0 - cerebral cysts
  • ICD-11: 8D67 - intracranial arachnoid cyst
Epidemiology
Sites
  • Arise within both cranial and spinal meninges
  • Most are supratentorial and found in the middle fossa (J Neurosurg 2013;118:222)
  • Other sites include retrocerebellar, convexity, cerebellopontine angle and spinal cord (J Neurosurg 2013;118:222)
Pathophysiology
  • Primary developmental cysts occur due to the splitting of arachnoid membranes in utero, resulting in abnormal collections of cerebrospinal fluid (CSF) (J Neuropathol Exp Neurol 1981;40:61)
  • Secondary cysts are less common and often occur after trauma, infection or surgery (Case Rep Orthop 2015;2015:250710)
  • Mutation of the FOXC2 gene has been reported in familial forms
Clinical features
Diagnosis
  • Computed tomography (CT) and magnetic resonance imaging (MRI) for radiologic assessment
  • Surgical resection is required for a definitive diagnosis
Radiology description
  • MRI is the diagnostic procedure of choice
  • Arachnoid cysts show low signal intensity on diffusion weighted imaging (DWI) and fluid attenuated inversion recovery (FLAIR) (Tani Girisim Radyol 2003;9:418)
  • No enhancement
Radiology images

Contributed by Saman Seyed Ahmadian, M.D.
T2 FLAIR MRI

T2 FLAIR MRI

T2 MRI

T2 MRI



Images hosted on other servers:

T2 MRI

Case reports
Treatment
  • Surgery if symptomatic
Gross description
Microscopic (histologic) description
  • Cyst wall is composed of a single layer of meningothelial cells and an outer collagenous membrane
  • Meningothelial cells often partially denuded and may not always be recognizable
  • Rare foci of meningothelial hyperplasia with or without psammoma bodies
  • Focal inflammation (rare)
  • Reference: Love: Greenfield's Neuropathology, 9th Edition, 2015
Microscopic (histologic) images

Contributed by Saman Seyed Ahmadian, M.D.
Cyst lining

Cyst lining

Meningothelial hyperplasia

Meningothelial hyperplasia

Calcification

Calcification

No apparent meningothelial cells

No apparent meningothelial cells

EMA

EMA

Virtual slides

Images hosted on other servers:
Arachnoid cyst, resection

Arachnoid cyst, resection

Positive stains
  • Meningothelial cells are positive for EMA
Negative stains
Electron microscopy description
Molecular / cytogenetics description
Sample pathology report
  • Cyst wall, excision:
    • Arachnoid cyst (see comment)
    • Comment: The histologic section shows a cystic lesion composed of a single layer of meningothelial cells with an outer layer of delicate fibrous tissue. The meningothelial cells are positive for EMA by immunohistochemistry, which confirms the diagnosis.
Differential diagnosis
Board review style question #1

A 71 year old patient with altered mental status had a 7.6 cm cystic lesion in the left frontoparietal convexity. The cystic lesion was excised. What immunohistochemistry confirms the diagnosis?

  1. Cytokeratin
  2. EMA
  3. GFAP
  4. Synaptophysin
Board review style answer #1
B. EMA. The histologic section shows a cystic lesion with a single layer of meningothelial cells with flattened nuclei and delicate fibrous tissue suggestive of an arachnoid cyst. The meningothelial cells are positive for EMA.

Comment Here

Reference: Arachnoid cyst
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