Hi, I am an American Board Certified Neurologist with vast experience in diagnosing & treating all types of neurological & other medical conditions including the concerns of “worsening moodiness, temper and personality change in your son” you have mentioned here and I am very glad to help you with your health concerns.
I have tried to answer your questions/concerns one by one below here;
1) so don't know what caused that cyst and if it is still there.
There are different types of cysts in the brain, and even prior head traumas too can cause cysts in the brain which are called post traumatic cysts. He did suffer from some head injuries when he was infant so trauma induced cyst is a possibility too. These type of cysts generally are not expected to grow, they generally resolve after some time
Another type of cyst is called is Arachnoid cyst. These are considered as congenital cysts means people are born with them. These type of cysts in general remain of the same size throughout life but rarely they can increase in size and start causing symptoms.
There are many other types of cysts in the brain and called as Pineal cysts, Choroidal fissure cysts etc.
As you see there are varieties of cysts related to the brain. And some of them can grow further, some of them do not grow. Those which can grow further can cause pressure effect on the area of the brain where they are located and cause neurological symptoms. If a cyst is causing pressure on certain parts of the brain like temporal lobe, or frontal lobe, or areas like hypothalamus etc it can cause changes in the mood, emotions, personality and behaviors etc
2) i just don't know if he needs to see a neurologist to have another mri done to see if that cyst is still there or not?
Yes it is good idea to see a neurologist now. As pointed above certain cysts can grow further and can cause the type of symptoms he is having, so seeing a neurologist is recommended now. And he also needs an MRI scan of the brain to see what is the exact status of the cyst - whether it has grown further or not, and also to look for any other new health conditions affecting the brain that may be causing his manifestations.
3) could it be maybe his b vitamin levels are low or something-else?
At this moment there are many different conditions that can cause his manifestations, so he needs a thorough further evaluations which should include a neurological evaluation and brain MRI scan as mentioned above, and also we need to explore other possibilities for example vitamin deficiencies too can cause his manifestations, for example vitamin b12, or folate, niacin etc vitamin deficiencies can cause these type of manifestations he is having. I am not sure how far he has already been investigated, even thyroid diseases too can cause his manifestations, so if not already checked then he also needs testing for his thyroid function too, along with blood vitamin levels.
To summarize once again, yes his symptoms can be related to the cyst, he needs a neurological evaluation, he needs an MRI scan of the brain to see whether the cyst or any other neurological/brain conditions causing his new manifestations, and also he needs additional evaluation to rule out vitamin deficiencies, thyroid issues etc, and then treated appropriately depending upon the test results.
Please let me know if you have any further questions, and please click a positive rating (preferably 5 Star/Excellent) to credit for the time & effort put by me in answering your health question, and this is the only way I will be credited for my service to you. If you have follow-up or additional questions you can ask them after the rating too.