Hello ! I understand your concern. A sub arachnoid space diffusion on MRI scan can be caused by a brain disease including sub arachnoid hemorrhage, meningitis, leptomeningeal metastases, acute infarction, and severe arterial occlusive diseases such as moya-moya disease. But it can also be a mistake during the examination, called in our medical language Artifact . This means that there is nothing wrong , but the MRI looks not normal by a mistake of evaluation by the machine . You have only have seizures, not any other troubel as I understand. I would like to know if you have had good result on medication for the seizure frequency. When seizures don t respond to different therapy , it can be an anatomic problem the cause, and it will be visualized on the MRI. In my opinion a second brain MRI would be necessary to rule out any artifact of MRI . I suggest a good neuro-radiologist consulted both the old and the new MRI to exclude any artifact of the examination. If the image is the same , the underlying cause should be searched. Hope to have been helpful! Thank you for using HCM! Best wished, Dr. Abaz Quka