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WBFO brings you NPR's live coverage of the Republican National Convention tonight and tomorrow night from 9pm-11pm.

Brain Condition Afflicted Sen. Johnson Suddenly

ROBERT SIEGEL, host:

As we've heard, Senator Tim Johnson has been diagnosed with AVM, arterial venus malformation, and we're going to hear more about that condition now from Dr. Jay Mohr, who's director of the Doris and Stanley Tannenbaum Stroke Center at Columbia University Medical Center in New York. Welcome to the program.

Dr. JAY MOHR (Columbia University): Thank you for the invitation.

SIEGEL: You study AVM at a stroke center. Can you just explain to us first what the relationship between AVM and having a stroke is? Is it correct to say that there has been a stroke here, did you know?

Dr. MOHR: Yes, a stroke can be caused by blockage of an artery in about 70 percent of cases and the others are caused by some form of hemorrhage, a small number of them explained by bleeding into this tangle of arteries and veins embedded in the brain is called an arterial venus malformation.

SIEGEL: That malformation, you've used the word tangle to describe it.

Dr. MOHR: Well tangle is, I think, an easily understood term to indicate that the arteries and veins are linked together in a variety of ways, but typically not with the usual smaller vessels called capillaries that help regulate the pressure and flow from the high flow arteries to the low flow veins.

With no capillaries, the arteries can flow directly to the veins and it's a bit like hooking a hot water line or cold water line to the waste pipe in your home.

SIEGEL: How many people would suffer from something like this typically?

Dr. MOHR: Well, as far as we can know from epidemiological studies that we've done here in the New York area, about 1.5 per 100,000, or 15 or so per million, actually harbor, have in their head, a brain arterial venus malformation and about a third of them present with bleeding and the other two are discovered incidental to brain imaging done for a different purpose.

SIEGEL: If you discover that somebody does have an arterial venus malformation and they haven't experienced any symptom, could you do something to prevent a hemorrhage?

Dr. MOHR: Yes, you certainly could. Two are being discovered unbled for every one that's bled and the uncertainty of whether we should intervene to extract the malformation by surgery, block its arterial flow by interventional procedures with catheters, glues and the like, or refer them for radiation therapy to try to damage the vessels so that they would clot themselves off has been of such a problem in management decisions that the National Institutes of Health recently funded us for a large, international 100-center trial to try to decide what the best treatment is or whether to treat before bleeding.

SIEGEL: Well, let's turn now to what little we know of Senator Johnson's condition. What would the questions be that doctors would want to have answered right now about his condition post surgery?

Dr. MOHR: Well, they'd like to know whether the AVM is small, whether it caused its hemorrhage by simply expanding in the space of the AVM and not damaging adjacent healthy brain or whether the AVM actually, in bleeding, vented or released or relieved some of its pressure by bleeding down into the brain cavities called ventricles, which usually contain nothing but spinal fluid. If it vented or bled into the ventricular system, it might simply have depressurized itself and the surgical removal of the AVM could be accomplished with minimum injury to the healthy adjacent brain.

SIEGEL: You're saying it's possible that the brain on its own could have drained out the situation?

Dr. MOHR: Yes.

SIEGEL: That it could have had its own fluids do the job?

Dr. MOHR: Yes. Many of these AVMs or arterial venus malformations, drain themselves into the venus systems on the inner walls of the brain and if the AVM breaks or bleeds or leaks, sometimes the blood can track into this ventricular system with minimum effect on the healthy brain.

SIEGEL: That's a good outcome.

Dr. MOHR: That's what we certainly hope has happened.

SIEGEL: I've heard though that a patient in the situation that Senator Johnson's in can appear to be comatose at this point.

Dr. MOHR: Yes, and if the - let's just say the best thing happened to him and he bled largely into the ventricular system, the blood would add to the volume of the ventricular system, inflate them, stretch the adjacent brain structures, causing a condition which in children is called hydrocephalus. And if the blood is drained off, the pressure is relieved and whatever effect was due to the short lived hydrocephalus would be reversed, which is of course what we hope happened.

SIEGEL: Well, Dr. Mohr, thanks a lot for talking with us.

Dr. MOHR: Oh, grateful for the opportunity.

SIEGEL: That's Dr. Jay Mohr of Columbia University, where he's at the stroke center. He was talking to us about the condition of AVM, arterial venus malformation, the condition with which Senator Tim Johnson has been diagnosed. Transcript provided by NPR, Copyright NPR.