Hi lsgoodchild,
Welcome to the NeuroTalk Support Groups.

As well as the Forum that Darlene has suggested you might also try searching in the subsection area called
Other Diseases & Concerns

There are separate areas there for Colloid Cyst, Tarlov Cyst etc..
I just ran a search there for Arachnoid Cyst and there are some older posts that may have information in them that can help you.

Also found some in the
Spinal Disorders & Back Pain Forum

If you need help to navigate NeuroTalk, please just post back and someone will be sure to help you out.