It's a tumor
Sen. Ted Kennedy's seizure over the weekend was caused by a malignant brain tumor. From AP:
Doctors say tests conducted after Kennedy suffered a seizure this weekend show a tumor in his left parietal lobe. They say preliminary results from a biopsy of the brain identified the cause of the seizure as a malignant glioma.
His treatment will be decided after more tests, but the usual course includes combinations of radiation and chemotherapy.