A pineal gland cyst can be benign or it can cause trouble. Some reports mention pineal gland cysts being asymptomatic until there is a head trauma. Head trauma can cause them to put pressure on the pineal gland or there structures. PGC's of 5mm or less are usually benign but commonly found in as much as 4% of MRI's.
Intra Cranial Pressure can be effected by them. This can lead to head aches and visual disturbances.
The challenge for you is how this can complicate a WC claim. Your attorney should be researching this to find out how to proceed.
I am not surprised that the MRI was normal otherwise. You may see if you can get a review of the images by a top of the line neuro-radiologist or neurosurgeon. They can easily email the images to a specialist anywhere in the world for an expert opinion. Maybe the doctors at this place can review your images.
http://www.skullbaseinstitute.com/pineal-tumor/
My best to you.