Unfortunately, it is not possible for me to make a specific diagnosis, as I am not involved in your husband's care. Also, it is not clear to me if he is currently undergoing chemotherapy (which often causes nausea).
If it hasn't been done already, then a CT scan or MRI scan of the brain would answer your question.
I hope that additional treatment can be offered to your husband to relieve his discomfort.
Sincerely/ Robert A. Wascher, MD, FACS
www.doctorwascher.com
www.oncoguard.com