Surgery for Cerebral Arteriovenous Malformation

WASHINGTON, Dec. 14 -- The stroke-like symptoms suffered by Senator Tim Johnson, a Democrat from South Dakota, were caused by a congenital arteriovenous malformation, his office said today.

Sen. Johnson underwent brain surgery during the night, after experiencing an episode of apparent confusion and transient aphasia Wednesday as he was speaking with reporters in a telephone briefing. He recovered enough to complete the call, and then walked to his office, where he complained of feeling unwell and had difficulty lifting his right arm.

A physician called in to consult told Johnson's staff that he may have had a stroke or heart attack, and the Senator was taken by ambulance to George Washington University Hospital.

There, after a stroke or heart attack were ruled out, Johnson underwent surgery to evacuate excess blood from the AVM, the relatively common cererbrovascular abnormality, and to cauterize bleeding, said Adm. John F. Eisold, M.D., attending physician to the U.S. Capitol.

Therapeutic options for AVMs include sterotactic computer-assisted microsurgery, embolization, and stereotactic radiosurgery with a "gamma knife" or "cyber knife."

According to Johnson's staff, he was awake during the ambulance ride. A statement said that the operation was successful and that Johnson was "recovering without complication" at George Washington University Hospital. If Johnson were incapacitated, the Democrats could lose their newly won control of the Senate.

"His ability to recover will depend on which side of the brain was affected by the hemorrhage and the AVM" commented neurologist Michael A. Williams, M.D., of Johns Hopkins in Baltimore.

"If it's on the left side, then which part of the left side," he added. "His ability to communicate may be more likely to be affected if the left side was involved and if that's the side of his brain where he has language function."

In an email reply to a request for comment, Dr. Williams, not involved in Johnson's care, said, "AVMs are often silent, asymptomatic, and therefore undiagnosed until a hemorrhage occurs, or some other symptom occurs that results in the person getting a CT or MRI scan of the brain that reveals the lesion."

Arteriovenous malformations are congenital vascular abnormalities, and are so called because they consistent of tangles of abnormally connected vessels, with fistulas rather than capillaries forming arterial-to-venous connections, resulting in overly rapid blood flow that does not allow for proper oxygenation of tissues.

The abnormal vessels are also subject to leakage and rupture, and can lead to intracranial bleeding that can vary in severity according to where the defect occurs.

AVMs are estimated to occur in the brain or spinal cord of about 300,000 Americans. Most of the abnormalities are asymptomatic, however, and are discovered only incidentally (for example, on autopsy or during surgery for a non-related condition), according to the National Institute of Neurological Disorders and Stroke (NINDS).

But in about 12% of people who have them, AVMs can cause symptoms that vary in severity according to the location of the defect, and may include ataxia, apraxia, dizziness, visual disturbances, including loss of visual field or an inability to control eye movements, papilledema (edema of the optic disk), aphasia, paresthesias, memory deficits, confusion, hallucinations, or dementia.

Each year, approximately 2% to 4% of neurological AVMs rupture or hemorrhage. The hemorrhages may be microscopic and cause only minor, limited damage, or could cause a massive disabling or fatal hemorrhagic stroke. The NINDS notes that approximately 2% of all hemorrhagic strokes reported annually arise from AVMs.

AVMs by their sheer mass may also compress surrounding brain structures or nerves, and can constrict the flow of cerebrospinal fluid by distorting or obscuring ventricles in the brain.

The lesions may form nearly anywhere in the CNS. In the brain, they often arise from vessels in the dura mater or pia mater. The etiology is unknown, but they are believed to form during embryonic or fetal development, according to the NINDS.