arachnoiditis and pain pump

i have arachnoiditis. i've had one surgery since the arachnoiditis was discovered on MRI. i had fusion surgery at L4-S1. i had scarring on the right nerve root at L5-S1 from a microdiscectomy, and after the fusion, i had awful scarring on the left. i have been in pain almost since the fusion, and i mean awful pain. the only way i can get relief is to stay in bed. my pain management doctor has suggested i get a pain pump. i'm worried that this might worsen the condition, but he says it's just about the only way to deal with the pain and hopefully become more active. my family doctor said that the pain pump would be a more localized treatment for the pain, and i wouldn't be having the medication actually reach my brain. i'm also worried about the pressure of the CSF. wouldn't putting medication into that area increase the pressure of the CSF and possible cause a cyst? i need more information, and it's very hard to come by!