My son is now 21 months of old. He was always (Height and head Circumference) on the 97th growth curve and my head is big as well. Specifically, between 10 to 15 months, his height was off the curve (i.e. over 97th curve). From the beginning my son could not sleep very well and he used to wake up many times during the night. But in last three months he had many night terrors (i.e. awakening with crying and screaming after roughly 3 hours of sleeping). He had three times similar night terrors before his 18th month but recently almost twice a week he experiences the night terrors. My son just was examined by a pediatric neurologist and the EEG result was Mild abnormal (Sleeping then taking EEG for 20 minutes). His doctor prescribed him Clonazpam 0.5mg/day for two weeks then we should increase the dosage to 1 mg (The diagnosis was a kind of seizures or night terrors). Then for better diagnosis we just had a Brain MRI of my son and the report of the MRI is attached to this question. I am really worried about two items of the MRI report, 2nd and 4th items as follows:
2- “There is slight increased subarachnoid space in frontal lobes.”
4- “Mild signal abnormality in foreceps major is seen as well as linear abnormality in left cereberall hemisphere the latter may be due to small venous malformation.”

My question is;
Do the mentioned items in MRI are related to the night terrors or any kind of seizures?
If yes, how intense is this problem according to the Mild abnormal EEG and the MRI report? Is it a permanent disorder?

Please note that we also were worried six months ago about autism disorder. My son had some signs of flipping hands and abnormal excitements when watching TV before his 18th month. So at his 15th month, before he could walk, we were worried about ADS and based on some exams he was evaluated as "little to no concerns" but close to border (i.e. score 9 in ADOS-T test at his 15 months). But now, in his 21st month, I feel he is very good in understanding and great in interactions with people. His language skill is not well but he can say many words and show his body and face parts when we name them. Also he can understand us very well when we ask him to bring some of his toys or our stuff. The only concern is that he sometimes loves to do repetitive things, e.g. going and coming back in one straight line many times even though we can easily distract him when we call him.

In advance I really appreciate you for your considerations and answers.