"He remains in good spirits and full of energy."
The 76-year-old Massachusetts Democrat was hospitalized Saturday morning after suffering a seizure at his family's compound at Hyannisport, Massachusetts.
"Preliminary results from a biopsy of the brain identified the cause of the seizure as a malignant glioma in the left parietal lobe," according to a statement from Massachusetts General Hospital.
Malignant glioma is the most common primary brain tumor, accounting for more than half of the 18,000 primary malignant brain tumors diagnosed each year in the United States, according to the National Cancer Institute.
A tumor in that area of the brain could affect Kennedy's ability to speak and understand speech, as well as the strength on the right side of his body, CNN's Dr. Sanjay Gupta said.
The usual course of treatment for Kennedy's type of tumor includes radiation and chemotherapy, Dr. Lee Schwamm, vice chairman of the Department of Neurology at Massachusetts General Hospital, and Dr. Larry Ronan, primary care physician, said in a statement.