Curing brain aneurysms by reconstructing arteries

A brain aneurysm is a tiny bubble or bulge off the side of an artery on the brain’s surface. It may grow undetected, the product of blood vessels weakened by high blood pressure, cigarette use, inherited genes, or (in most cases) just bad luck. While it is believed that about one in 50 Americans harbor a brain aneurysm, most will never know it, and their aneurysm will never cause a problem. But rarely, the arterial wall of an aneurysm can become so thin that it bursts, spilling blood over the brain’s surface. This is the most feared outcome of a brain aneurysm and is what drives the urgency in treating many brain aneurysms, even if found accidentally.

Any quick online search will tell you why. More than one third of people who suffer a ruptured brain aneurysm will die as a consequence. Of those who survive, the majority will be left with a disability or neurologic deficit. The financial costs to society are high, and the emotional costs to patients and their families are even higher. Between the silent growth, potentially explosive nature, and the devastating consequences, brain aneurysms have been aptly termed “ticking time bombs.”

The treatment of brain aneurysms is aimed at disrupting blood flow into the aneurysm. This was traditionally done from the outside by pinching the aneurysm with a metal “clip” or from the inside by filling an aneurysm with metal “coils.” These treatments, however, were not uniformly successful or even possible with some aneurysms. This prompted physicians and engineers to experiment with a novel concept of treating a brain aneurysm indirectly by encouraging the blood flowing through an artery to stay within that artery and not enter the bulging aneurysm as it passed by. This was done using tiny stents, or mesh tubes that could be placed within a blood vessel in the brain across the origin of an aneurysm. As blood flow slows or stagnates within an aneurysm, it forms a clot and then eventually scars down, occluding the aneurysm. The density of the mesh turned out to be key – if the mesh was too dense it might inhibit flow into other normal branches that the brain needs for survival but if not dense enough, the aneurysm would continue to fill with blood and remain a danger. The perfect mesh tube would contour the artery, shepherding blood past the aneurysm and through the normal arteries. Once that aneurysm clotted and scarred, the mesh would then serve as a scaffold, allowing cells of the inner lining of the artery, known as the endothelium, to grow across the aneurysm. The artery would, in effect, reconstruct itself.

Careful experimentation and product design eventually led to the production of several commercially-available devices, now known as “flow diverters.” The first and most widely available in the United States was known as the Pipeline Embolization Device, which received its Federal Drug Administration approval based on the results of a prospective trial known as the Pipeline for Uncoilable or Failed Aneurysms (PUFS) trial. This single-arm trial tested the use of this device on large and giant aneurysms that were considered otherwise untreatable or had failed prior attempts at conventional treatment. The initial results were exciting in that over 70% of treated aneurysms were occluded at a six-month follow-up. This result, however, came with a risk of stroke or death in 5.6% of the patients, which was considered comparable to other treatments.

Long-term follow-up of the original patients from this trial was recently published, showing overall aneurysm occlusion rates of greater than 90% after five years with no additional major complications after the initial six-month follow-up. Importantly, treatment with flow diverters was durable, and there were no instances of an aneurysm recurring after successful occlusion.

The recent success of flow diverters has been followed with development of many new devices and technologies all aimed at making aneurysm treatment safer and more effective. There is no one treatment that will cure every aneurysm, but each additional technology provides one more tool that aneurysm surgeons can use to stop these ticking time bombs before it’s too late.

Featured image credit: Surgical instruments by tpsdave. CC0 public domain via Pixabay.