Brain Arachnoid Cysts

The arachnoid membrane is one of the membranes that cover the brain and the spinal cord. Arachnoid cysts can develop under this membrane around the brain or its ventricles. It is rare for an arachnoid cyst to form on the spinal cord. They are filled with csf and are benign.

If an arachnoid cyst is present at birth, it's considered primary. A primary arachnoid cyst is caused by early abnormal development in the fetus. Secondary cysts are those caused by some kind of injury or disease, but these are more uncommon. Most arachnoid cysts are on the outside of the temporal lobe. Males get them 4 times as often as women.

If the cyst isn't causing damage and no symptoms are present, no treatment may be necessary. If the cyst is causing damage or symptoms, such as vomiting, headaches, vertigo, seizures, hearing or vision impairment, then drainage of the fluid is necessary. Usually the symptoms go away after treatment. MRI scanning is used to diagnose whether a cyst is arachnoid , although CT scans for injuries sometimes initially identify that some type of cyst is present.

This first photo is a sagittal view of an MRI demonstrating an arachnoid cyst on the third ventricle. This second photo is an axial CT showing a different patient with a large arachnoid cyst.