Hello Gents! I have a medical question (again!) that I am confused about, and unfortunately haven't been really given a straight answer due to the legal issues potentially behind this. For that matter, I will try to word this with the background of my question and in such a manner that I won't be breaking legal grounds, for my lawyer's sake! This is for my own knowledge as well and won't be used in my arguments.

Let's say Johnny got into a car accident, rear ended at 50mph when his car was at a dead stop. Before this, Johnny had a few injuries from his military service. A couple of years before the accident he was seen for a horrible migraine and was given a brain / spine CT scan and a spinal tap, which both proved inconsequential.
After the accident Johnny complained of numbness in his hands and feet, plus urinary problems and very frequent headaches and spine pain. His diagnosis was a very large subarachnoid cyst, from the base of his brain to his lower back that also pressed on his spinal cord.
In a conversation with the doctors, one doctor proclaimed that these cysts are typically chronic in that he probably had it from earlier. Johnny told the doctor of the previous scans / tests which the doctor claimed meant nothing.
Given Johnny's onset of symptoms after the accident, would it be safe to assume that the injury caused the cyst, or at least aggravated the cyst from the injury? Johnny reported his back, hip and head hurting after the injury.