The reasoning (for us) behind the MRI and spinal tap was to determine if Vegas had a brain tumor. We opted to NOT do it. Our neurologist told us if he had a tumor, we would be able to tell in the coming months. He would no longer be able walk or stand. He would start to stumble around. Thankfully...the test was unnecessary. Good luck and give him kisses for us. Please let me know what they say. I'm sending positive thoughts your way.