The recent hospitalization of Sen. Tim Johnson (D-SD) has put the spotlight on congenital cerebral arteriovenous malformations. While these are rare -- occurring in 2% of the population -- they can be deadly.
The recent hospitalization of Sen. Tim Johnson (D-SD) has put the spotlight on congenital cerebral arteriovenous malformations. While these are rare - occurring in 2% of the population - they can be deadly.
"Many physicians go a career in medicine without seeing a dural arteriovenous malformation. That's how rare they are," said Dr. Wayne F. Yakes, director of the Vascular Malformation Center in Denver and one of the few interventional neuroradiologists dedicated totally to treating vascular malformations.
Congenital AVMs occur when the primitive vascular system in the fetus incompletely resorbs before the newer, more complex system appears. This nest of nonfunctional blood vessels consists of veins and arteries, but no connecting capillaries. Consequently, the high-pressure arterial blood is shunted directly into the low-pressure venous system, which can weaken and burst, spilling blood into the brain.
About half of all AVM hemorrhages are significant, with permanent disability in half of these cases and death in the other half. Generally, an AVM will hemorrhage between the second and fourth decade of life.
Johnson, 59, was hospitalized and underwent surgery on Dec. 13. Yakes said it's unusual to operate on an AVM so quickly after it bursts. He prefers to wait until swelling in the brain has subsided.
Dr. Anthony Venbrux, director of cardiovascular and interventional radiology at George Washington University Hospital and a member of the senator's operating team, agrees with Yakes.
"Normally, we wouldn't operate so quickly. But extenuating circumstances necessitated we do so," Venbrux said.
Venbrux assisted Dr. Vivek Deshmukh, a neurosurgeon with special expertise and subspecialty training in cerebrovascular and endovascular neurosurgery, and Dr. Anthony Caputy, chair of neurosurgery at GWU.
A statement released by Johnson's office said the senator underwent successful surgery to evacuate the blood, stabilize the AVM, and relieve pressure on the brain. CT scans showed that the pressure in Johnson's brain had been relieved and that the bleeding had stopped.
To reduce the risk of pulmonary embolism, doctors placed a removable MRI-compatible filter in the senator's vena cava that will stay in until he makes a full recovery, Venbrux said.
"AVMs are very fragile and have a propensity to bleed or rebleed. Because they are often a tangle fed from multiple arterial territories, it's hard to completely eradicate them," he said.
Because Johnson had symptoms suspicious of a stroke, he would have first undergone a noncontrast head CT to rule out hemorrhage. If hemorrhage is found, as was the case with Johnson, it negates the use of thrombolytics.
The AVM would not have shown up on the noncontrast head CT because fresh blood obscures detailed anatomy. Once the blood is cleared, the team might call for MR angiography to assess the brain's vascular territory. Almost all patients with AVMs get digital subtraction angiography because it allows physicians to do embolotherapy if necessary, Venbrux said.
AVMs can be embolized with beads, coils, or glue materials. While this approach rarely cures the problem, it can make subsequent surgical removal of an AVM significantly safer, or it can reduce the size of an AVM to a volume with a higher radiosurgery efficacy. Stereotactic radiosurgery takes about three years to complete and has a 15% failure rate. It's usually reserved for deep lesions in difficult operating areas, Yakes said.
Unlike glues or coils, ethanol as an embolic agent has the potential to prevent recurrence, thereby eliminating the need for surgery. When glue is used to occlude the vessels, endothelial cells sense the decreased oxygen and send out angiogenesis factor, which stimulates new blood vessel formation, and chemotactic cellular factor, which mobilizes white blood cells to clear out cellular debris, also known as recanalization. While ethanol promotes clotting, it also destroys the endothelial cells, stopping the processes of recanalization and angiogenesis, Yakes said.
AVMs are graded on a scale of 1 to 5, with the latter being the most dire. Small (<3 cm), medium, and large (>6 cm) lesions are assigned 1, 2, or 3 points, respectively. An AVM in close proximity to an eloquent brain region is assigned 1 point, with 0 points for noneloquent proximity. One last point is assigned if the AVM drains into the deep venous system. Surgeons determine the grade by adding the points in each of the three categories.
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