This question is outside of my area of expertise. The adenoidal tissue is soft tissue surrounding your oral/throat cavities. They are similar to lymph nodes in other areas of the body. If they are hypertrophic it may simply mean that he was recently exposed to an cold, since when they are active they increase in size. If you are concerned about this, then consulting with a sinus doctor (ENT) is reasonable. They can look at the films and examine your son. This will help to put your concerns to rest. Good luck.
Amy