Arachnoid Cyst

Basics

Basics

Basics

Description

Description

Description

  • Histologically benign, cerebrospinal fluid (CSF)-filled, space-occupying lesion of the central nervous system
  • May be intracranial (most are supratentorial), spinal, or perineuronal
  • Classification (1)
    • Primary (congenital)
      • Intra- or extradural, found around the brain or spine
      • Often no communication with the subarachnoid space
      • Contains clear CSF-like fluid
      • Cyst walls are meningothelial cells often capable of secreting CSF.
    • Secondary (acquired)
      • CSF sequestration due to inflammatory or traumatic processes
      • Surrounded by arachnoid scarring
      • Contains CSF and possibly hemosiderin-stained or inflammatory cells
      • Usually communicates with the subarachnoid space
  • System(s) affected: central nervous; peripheral nervous
  • Synonym(s): leptomeningeal cysts

Epidemiology

Epidemiology

Epidemiology

  • Diagnosed most frequently in the first 2 decades of life (1)
  • 2:1 male predominance
  • Middle cranial fossa cysts are most common, with an increased incidence on the left side (2,3).

Prevalence
0.2–1.7%, although as imaging becomes more common, a prevalence up to 2.9% is suggested, with peaks at age 1 and 5 years (3).

Etiology and Pathophysiology

Etiology and Pathophysiology

Etiology and Pathophysiology

  • Several theories of arachnoid cyst formation (4)
    • Agenesis of part of the brain
    • Defect in the arachnoid development, leading to membrane splitting or duplication creating diverticula
    • Failure of temporal embryonic meninges to merge as the sylvian fissure forms
    • Defect in condensation of the mesenchyme from abnormal CSF flow
    • Arachnoid adhesions due to trauma, meningitis, mastoiditis, subarachnoid hemorrhage, or iatrogenic causes
  • Cyst growth also has many suggested causes (4):
    • One-way ball-valve allowing CSF to enter but not exit the cyst (CSF obstruction and vent mechanism) (5)[A]
    • Distribution of arachnoid trabeculae leading to trapping of fluid in the cyst
    • Fluid production by cells lining the walls of the cyst
    • Osmotic gradients due to higher protein content of cyst fluid (6)
  • Symptoms are due to compression and mass effect on adjacent brain or spinal cord structures, interruption of CSF flow, or intracyst/subdural hemorrhage.
  • Primary arachnoid cysts are congenital.
  • Secondary arachnoid cysts are associated with inflammation and trauma.

Genetics
No specific genetic association with arachnoid cysts, although bilateral cysts may occur in Hurler syndrome

Risk Factors

Risk Factors

Risk Factors

  • Primary arachnoid cysts are congenital.
  • Risks for secondary arachnoid cysts
    • Inflammation from infection, hemorrhage, or iatrogenic causes
    • Trauma from lumbar puncture, anesthetic procedures, or intradural surgery

Commonly Associated Conditions

Commonly Associated Conditions

Commonly Associated Conditions

Rarely, associated with the following:

  • Hydrocephalus
  • Chronic subdural hematoma
  • Dysgenesis of the corpus callosum
  • Malformation of the cerebral venous system
  • Glutaric aciduria type I
  • Trisomy chromosome 12
  • Neurofibromatosis
  • Autosomal dominant polycystic kidney disease

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