Hi Andy,

Wow, so strange to hear your story, and I can understand what you are talking about! My cyst was similar to yours, A Dandy-Walker variant Arachnoid Cyst in the Posteror Fossa. Maybe not quite as big as yours, but causing many symptoms, and it took nearly 2 years to get a diagnosis. Finally an MRI found the cyst.
So glad to hear that you got the treatment you needed for your Cyst. I've heard stories where some people can't get a Neurosurgeon to take their symptoms seriously and operate. So glad you found a good Neurosurgeon.
I didn't have a shunt put in, I had a cyst fenestration. I hope that the shunt works for you and there aren't any problems. Yes, it will take time for it to work, to relieve the symptoms, and the pain. If you have had some improvement in 2 weeks, then things will only get better!

~Jaime~