My MRI didn't show anything concerning my concussion, but it did show a severe sinus infection.

I knew that I had had a cold, but my PCS had masked the other symptoms of what turned out to be a very severe sinus infection. My neurologist told me the bacteria in my sinuses was close to penetrating the skull and affecting my brain.

An MRI is nice just to rule out the other possibilities. It gives you less to worry about.