What causes arachnoid cysts?

What causes arachnoid cysts?

Most arachnoid cysts appear at birth (primary arachnoid cysts). They usually occur in the womb during the early weeks of pregnancy. Healthcare providers aren’t sure what causes arachnoid cysts to form.

Sometimes arachnoid cysts run in families, so providers think genetics may cause them to develop. People who have certain health conditions, such as arachnoiditis or Marfan syndrome, may be more likely to develop arachnoid cysts.

Less often, arachnoid cysts grow after some sort of childhood head trauma, such as a brain injury, surgery or infection. When this happens, providers call them secondary arachnoid cysts.