Spinal meningeal cysts are diverticulae of the arachnoid or dura mater or of the nerve root sheath. They are uncommon, usually asymptomatic and invariably found incidentally at MRI (that has been performed for another reason).
The cysts contain CSF and have thin walls. They may be intradural or extradural and may contain neural tissue. The spinal meningeal cyst classification uses these features to separate the different type of cysts.
They cysts are usually asymptomatic, but if they are large, they may cause mass effect and symptoms relating to compression of local structures, e.g. nerve roots.
CSF pulsation can also remodel the surrounding bone, e.g. sacral canal.