What percentage of arachnoid (cerebrospinal fluid-filled sacs) cysts cause symptoms?

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Last updated: May 24, 2025 • View editorial policy

From the Research

Approximately 1-2% of all cystic spinal masses/tumors are arachnoid cysts, and the majority of them are asymptomatic, but when symptoms do occur, they can cause significant morbidity and mortality. The exact percentage of arachnoid cysts that cause symptoms is not well established, but it is estimated that only a small percentage of them become symptomatic 1. Arachnoid cysts are fluid-filled sacs that form between the brain or spinal cord and the arachnoid membrane, one of the three meningeal layers covering the central nervous system. Most arachnoid cysts are discovered incidentally during brain imaging performed for unrelated reasons. When symptoms do occur, they typically result from the cyst's size, location, and whether it's causing pressure on surrounding neural structures. Common symptoms include headaches, seizures, nausea, vomiting, dizziness, hearing or vision problems, and balance issues. In children, arachnoid cysts may also cause developmental delays or changes in head shape. The likelihood of symptoms increases with cyst size and when cysts are located in areas where they can obstruct cerebrospinal fluid flow or compress important brain structures. Some key points to consider when evaluating arachnoid cysts include:

  • The location of the cyst, with thoracic, lumbar, and cervical spine being the most common locations 1
  • The size of the cyst, with larger cysts being more likely to cause symptoms
  • The presence of symptoms, such as intracranial hypotension, radiculopathy, and/or myelopathy 1
  • The results of imaging studies, such as MRI and Myelo-CT, which can help to document the extent and severity of the cyst 1 Treatment is generally only recommended for symptomatic cysts and may include surgical options such as fenestration, shunting, or complete removal depending on the specific characteristics of the cyst 1, 2, 3, 4, 5.

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