He had bleeding in the brain.
Johnson, 59, suffered from bleeding in the brain caused by a congenital malformation, the U.S. Capitol physician said. He described the surgery as successful. The condition, usually present at birth, causes tangled blood vessels that can block the flow of blood or rupture.
“The senator is recovering without complication,” said the physician, Adm. John Eisold. “It is premature to determine whether further surgery will be required or to assess any long-term prognosis.”
Eisold said doctors drained the blood that had accumulated in Johnson’s brain and stopped continued bleeding. […]
Johnson’s condition, also known as AVM, or arteriovenous malformation, causes arteries and veins to grow abnormally large and become tangled.
The condition is believed to affect about 300,000 Americans, according to the National Institute of Neurological Disorders and Stroke. The institute’s Web site said only about 12 percent of the people with the condition experience symptoms, ranging in severity. It kills about 3,000 people a year.
More as it develops.