From what i understand (and anyone else feel free to chime in and correct me!) an AN begins to grow from the cells of the sheath of the vestibular nerve (CN VIII) and is benign (there have been a handful (about 5 I think) non-benign cases so tres rare). The AN starts growing in the internal auditory canal (IAC), as it gets too big for that area it starts to spill out into the cerebellopontine angle (CPA) and will in time begin to displace brain tissue and press into the brain stem. The tumour is very slow growing however some cases have a little growth spurt for whatever reason.
A CPA meningioma is also a benign tumour which grows in the cerebellopontine angle (CPA) and starts growing from the cells of the meninges (the protective covering of the brain). Exactly like AN's they are generally benign, slow growing and don't start spreading into the brain they just push on it a bit. AN's are more common than CPA meningioma's. Because the CPA meningioma's come from the brain lining and not the nerve cells, there is less chance of hearing or facial nerve damage during surgery.
There's probably heaps more difference than that - but that is just my simple understanding. My friend's mum had a CPA meningioma and had a very similar surgery to me. We're both fine and dandy! Not sure about radiation, I'm sure someone else will be able to help you with that one!
Take care
JB