As explained by NINDS, cerebral aneurysms occur when flowing blood causes a weak spot in a brain blood vessel to balloon out, putting pressure on nearby nerves. Many aneurysms are caused by congenital abnormalities in the arterial wall, while conditions that affect the vascular system, such as hypertension and atherosclerosis, increase the risk. Brain aneurysms are more common in women than in men, and likewise among 30 to 60 year olds.
Further according to NINDS, unruptured brain aneurysms occur in two percent of the population and present no symptoms in most patients, but the results of rupture are dire. Forty percent of ruptures are fatal within the first 24 hours of bursting, and two-thirds of survivors suffer from permanent brain damage. Delayed complications include vasospasm, a constricting of the blood vessels in the brain that causes stroke.
NINDS also says that smaller aneurysms are typically asymptomatic, but as aneurysms grow and create pressure on surrounding nerves and tissue, they can produce symptoms such as eye area pain, weakness or paralysis on one side of the face, and changes in vision. When the aneurysm bursts, the patient may experience a sudden and intense headache (often described as "the worst headache of my life"), nausea, and loss of consciousness. An estimated 30,000 people experience burst aneurysms every year in the US, and for the vast majority of them, the presence of the aneurysm went undetected until the rupture. The annual risk of rupture of these aneurysms is less than 1 percent.
Currently, according to NINDS, there are two options once an unruptured aneurysm is detected:
- Microvascular clipping results in the permanent insertion of a metal clip in the brain to cut off the aneurysm's blood supply. This procedure is invasive and requires the removal of part of the skull, but results in a lower rate of recurrence. Clinical studies suggest this method is up to 90% effective.
- A related procedure, an occlusion, is when the entire artery leading to aneurysm is clamped off (occluded); this surgery occurs especially if an aneurysm has damaged the artery. This procedure can occasionally include the insertion of a bypass to reroute blood away from the occluded artery.
- Endovascular embolization is the more common and less-invasive procedure, in which a coil is threaded through the patient's arteries and into the aneurysm, destroying it there. Clinical studies suggest this method is up to 86% effective. This procedure, however, may have to be performed multiple times over the patients’ life to ensure the complete eradication of the aneurysm.
Both of these options carry a low risk of death, but clinicians point out that the decision regarding surgical intervention versus careful observation and monitoring is a difficult one. On the one hand, once an aneurysm ruptures there is a high probability of death or paralysis. On the other hand, many aneurysms will never rupture, and many patients will not want to risk a surgical procedure to remove an unruptured aneurysm.
As of 2013, no randomized trials exist to contrast the effectiveness of these two treatments, nor to demonstrate whether intervention or observation is the better clinical option. NINDS would be required to use the increased funding provided by this bill for comprehensive research into management of unruptured cerebral aneurysms. The stated goal of the appropriation is to “[study] a broader patient population diversified by age, sex, and race,” as enabled by the increased funding.
Other areas of research on unruptured cerebral aneurysms that increased funding could make possible include genome-wide association studies to detect genes associated with the disorder; similar genome studies to detect genes linked both to brain aneurysm and other disorders; environmental factors and their influence on aneurysm risk; and the effect of aspirin, an inflammation inhibitor, on the rupture of aneurysms.