K.L.
R.,
I am so sorry to hear that you, your son and your family must go through this. As a mother of a very premature baby who was born 3 months earlier, I share your pain. One way to decide whether or not to continue with the MRI depends on worst case scenario. What would happen if you did not get the MRI to find out the cause? I think that will answer your question. If the worst case is something you can handle, then albeit wait for it to go away or show other symptoms that require attention. Otherwise, I suggest getting the MRI. In the grand scheme of your son's life, this is but a small challenge. Babies are fighters. I have one. I know!
Take care! I wish your son well!
K