Per MSNBC, he has a brain tumor. No word on whether it's benign or malignant at this point.
UPDATE: Statement from neurologist:
He has had no further seizures. Some tests were inconclusive. However, preliminary results show a MALIGNANT tumor. Radiation and chemo are the common treatments. Decisions will be made after further analysis on the treatment.Sadly, per the MSNBC analyst, this is the worst kind of tumor to have. With brain surgery, of course, you have to be aware that speech and movement can be affected.