posterior fossa subarachnoid cyst is treatment needed

The MRI report says "There is a well defined, smoothly marginated structure, filling much of the right side of the posterior fossa. This is of or near CSF intensity on all sequences. It measures approximately 7.4 by 5.4 by 4.5 cm in AP, transverse and CC projections. The lesion attenuates with CSF on FLAIR images, shows increased diffusion on the diffusion weighted sequence, and does not enhance. It gently displaces the brain stem and the fourth ventricle to the left of the midline. It has a smooth scalloped margin with the right cerebellar hemisphere, which is probably developmentally small. Its imaging characteristics are typical of a realitively large subarachnoid cyst. There is no insinuation of the lesion in adjacent structures, or other imaging features to suggest an epidermoid tumor or other lesion."

This cyst is in our 12 year old son and I would like to know if this size of cyst needs to be treated? If so how are they treated? I know that this part of the brain deals with attention and our son has been diagnosed with add/adhd since he was 5 years old. Now he has been having violent outbursts, could this cyst be causing these problems? Should we be concerned with him playing football, or wrestling when school gets back in? Is there risk of the cyst rupturing and having fluid around his brain? How serious is this, life threatning? every question I asked our doctor was answered with I don't know or I don't think so and I am very uncomfortable with that. I want someone who knows what they are dealing with to explain this to me because I don't understand what the MRI report is saying.  Thank You in advance for taking some time to look at this.