MRI & bladder dysfunction....

My daughter (16  mos) has had a lot of urologic problems, including a failed reimplant surgery for grade V kidney reflux, and a grossly enlarged bladder.  She currently has a vesicostomy to stop recurrent kidney infections (8 in 10 months).  In July we did an MRI to rule out neurological problems.  The MRI came back negative, but the doctors still feel like her problems are caused by a neurologic defect, making her diagnosis a neurogenic bladder.  How can this be, if the MRI came back negative?  Is there other testing that we should do?  Should we be concerned about an underlying disease or defect?

Thank you!