My Dad Is 76, He Has Episodes Of Confusion That

My Dad is 76, he has episodes of confusion that lasts 2 - 3 weeks during this time he has had seizures. His confusion starts off mild but he becomes extremely confused and symptoms of psychosis, he has had Mari, cat scans, lumber tests but all come back clear, he has been diagnosed with epilepsy however family beleive something must be causing this behaviour, once he is over the confusion he returns back to his normal health. Could this be caused by a brain tumour.