Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
It sounds like your son was incidentally discovered to have an abnormal EEG and MRI while he was having a work up for sleep apnea. It sounds like he has been found to have cortical dysplasia. Besides unilateral sensory hearing loss and some speech delay, he doesn't sound like he has neurologic symptoms. I can understand how overwhelming this news must be to you.
Without the ability to take a full history and examine your son and review his MRI, I can not comment further on what he currently has but I would be happy to provide you with more information on cortical dysplasia.
Normally during development, nerve cells (neurons) migrate from one area of the brain to the other and form normal clefts and valleys on the surface of the brain. Sometimes, the neurons do not migrate normally but end up in areas that they should not be in. The group of disorders resulting from this are called "neuronal migration disorders", and the areas of the brain that do not develop normally are called "dysplasias".
Cortical dysplasias may be asymptommatic, not causing symptoms, such as in your son. Some people can have them and live with them all their lives without symptoms or consequences. However, they may also cause seizures. Most people think of seizures as convulsions, shaking all over. This is often the case, and that would definitely be something to look out for. However, if these occur at night you may not know about them; things to look for in the morning are unexplained bed wetting and tongue biting, which may suggest a seizure occured during sleep. Seizures occur in many shapes and forms and can be very subtle. For example, staring off in the middle of a sentence for 15 seconds then resuming the sentence may suggest a seizure. Episodes of staring with picking at the clothes or smacking the lips also could be seizures. I would suggest just to watch for any abnormal episodes or behaviors and report these to your neurologist.
It is also important to understand that some of the disorders of neuronal migration are associated with problems in other organ systems: if the nerve cells did not migrate properly, it is possible cells in other systems did not migrate properly as well. Annual eye exams would be a good idea. I'm not sure whether or not his hearing loss is related to the cortical dysplasia.
If your son does develop seizures, several medications to treat seizures, called anti-epileptic medications, are available. If he continues to have seizures, evaluation at a specialized surgical epilepsy center may be helpful: after extensive EEG monitoring and several imaging studies, if it is determined his seizures are coming only from the area of dysplasia, surgical removal of the dysplasia may be curative. However, surgery should be done after extensive evaluation: removal of his dysplasia at this time, without symptoms, or at a later time without extensive evaluation at a specialized epilepsy center may cause more harm than good.
Thank you for the opportunity to answer your questions, I hope you find the information I have provided helpful. Good luck.