Husband had neurology consult and MRI today. Why would we have to follow up in 6 months if the CT scan showed no problems?

The neuro was extremely thorough and we liked her a lot. I stepped out of the room during the MMSE. When I returned, the doctor told us my DH had scored a 25 of 30 on the MMSE, which is the lowest score of "normal." She did a few more tests with me present (which I did not understand...why didn't she do these when I was out of the room?) DH could not spell "world" backward (even though he had been rehearsing it since he could not do it at his PCP appointment a few weeks ago.) He could not close his eyes and touch his nose (he just missed on the right side). He could not do the fingers-to-thumb exercise. It was then that the neuro said she wanted a CT scan, wanted to follow up with him in 6 months and was very clear that I should call her if it seems to me that he was getting worse. I see on her notes on the MRI Imaging order that he tested "Romberg positive." What does that mean? I see the CT scan results on the portal and everything is normal on the CT scan, which means the neuro will not call us. Why would we have to follow up in 6 months if the CT scan showed no problems? Or does a CT scan only rule out stroke? Thank you for your responses.