Faculty at the Bernard and Irene Schwartz Interventional Neuroradiology Center have been leaders in the treatment of cerebral aneurysms for over two decades. Therapeutic modalities developed by members, such as the Neuroform and Pipeline devices pioneered by Dr. Peter Kim Nelson, have revolutionized aneurysm management worldwide.
What are cerebral (Brain) aneurysms and how do they form?
There are different kinds of aneurysms. Most aneurysms are felt to be “weaknesses” in walls of brain arteries which bulge out over time, as seen on an angiographic image of a typical “saccular” or “berry” kind of aneurysms, arising at a branch point of two arteries, as seen on the catheter angiographic image below:
Other, more complex aneurysms diffusely involve a whole segment of the artery, known as a fusiform aneurysm, such as this one:
Even rarer aneurysms can develop on smaller vessels, sometimes as a result of infection, known as mycotic aneurysms, like this one:
The actual mechanisms of aneurysm formation depend on aneurysm type and, in reality, for most aneurysms the true causes are still unknown. This is not the kind of uncertainty we like as patients or as physicians, however such are the facts. Most patients with brain aneurysms have no underlying disorder that we know of. On the other hand, many known disorders are associated with increased risk of forming aneurysms-polycystic kidney disease, sickle cell disease, and various connective tissue disorders are some examples. Common conditions which encourage aneurysm growth and increase the likelihood of rupture include hypertension and smoking.
When do aneurysms develop?
Most “saccular” aneurysms-the most common type-are discovered in middle-aged and older adults. This kind is very rare in young adults and extremely rare in children. When a saccular or fusiform aneurysm is found “incidentally”, during evaluation of some other problem (by MRI, most typically), the question of “how long has it been there” can usually only be estimated, unless previous imaging is available. There are many other rare types of aneurysms (such as the “mycotic” kind) which form for different reasons and at different times.
About 20-30% of patients have more than one aneurysm, and 5% will have three or more. In most cases, we don’t know the underlying reason; in a minority of patients a known predisposing disorder exists.
Overall, between 0.5% and 2% or adults have an aneurysm. Most of these patients have no family members with aneurysms that they know of. For those that do have a blood relative with an aneurysm or history of subarachnoid hemorrhage (“SAH” or brain bleeding), we usually recommend screening of first degree adult relatives with Magnetic Resonance Angiography (MRA) is usually advised. Normal MRA exams may need to be repeated at some intervals to make sure that new aneurysms do not develop.
How are aneurysms found?
With widespread use of MRI and CT technology in the US, many aneurysms are now discovered “incidentally”. Occasionally, aneurysms grow to be large enough to press on adjacent brain or nerves, producing symptoms due to “mass effect” which leads to its detection. Another important mode of discovery is the “sentinel bleed” – either a small hemorrhage (bleed) or a period of aneurysm growth which produces a headache. Unfortunately, a large number of aneurysms give no warning until they suddenly rupture, which typically leads to the feared “subarachnoid hemorrhage”
Most aneurysms are located on arteries which surround the brain in a compartment called “subarachnoid space”. Therefore, aneurysm rupture results in bleeding around the brain, known as “Subarachnoid Hemorrhage”. Not infrequently, bleeding also extends into the brain itself. The classic symptom of aneurysm rupture is the “worst headache of life”. It is truly the worst headache ever and there is nothing like it. The headache is caused by sudden rise in intracranial pressure as arterial blood begins to fill the spaces surrounding the brain. The rising intracranial pressure also has the effect of decreasing blood flow to the brain, which causes many patients to lose consciousness soon after developing such a headache. Other symptoms include vomiting, lethargy, and weakness.
A special group of aneurysms which are located inside the skull but outside of the sac which surrounds the brain (dural sac) can rupture without the catastrophic consequences of subarachnoid hemorrhage. Many of these aneurysms form inside a large venous structure at the bottom of the skull called “cavernous sinus”. Rupture of these cavernous aneurysms leads to establishment of a direct communication between the carotid artery (site of aneurysm) and cavernous sinus- a condition called “carotid-cavernous fistula” – usually manifesting itself as a sudden severe pain behind the eye, followed quickly by severe eye swelling and redness. Despite its dramatic presentation, this kind of rupture is usually less dangerous than subarachnoid hemorrhage. Yet other aneurysms can present with bleeding directly into (not around) the brain- mycotic and vasculitic aneurysms being of this kind.
Consequences of aneurysm rupture
The outcome depends on many factors- for example how much bleeding there was, location of aneurysm, age and general health of the patient, and subsequent medical care. Unfortunately, about 15% of patients die before reaching the hospital, and 40% will not survive the first two weeks, even under best available care. Of the survivors, more than half will be permanently disabled. Only a small minority of perhaps 20% will return to their pre-rupture employment and level of function. Why such grim statistics? Because the brain is a complex and sensitive organ, designed for performance in the sheltered environment of the skull, under carefully controlled conditions. It has a low tolerance for the kind of global injury caused by subarachnoid hemorrhage. It is simply not built to withstand lack of blood flow, high surrounding pressure, or irritation produced by bleeding for any extended length of time. Most damage caused by aneurysm rupture is sustained in the first minutes of the event. Even flawless subsequent care – and such care is extremely complicated and very often subject to setbacks and additional complications even in the best of centers – can only prevent future bleeding and help mitigate the harmful effects of the initial rupture to give the brain the best chance for ultimate recovery; it cannot reverse whatever damage was already done.
Will the aneurysm rupture?
That is the key question facing a patient with an unruptured aneurysm. We have no crystal ball to predict which one will rupture and when. The best advice we can give is based on studies which followed patients with different aneurysms for many years without treatment-either because of patient preference or because treatment was felt to be ineffective or too risky. What we learned-and continue learning-from these studies is that the risk of rupture depends primarily on the size and location of the aneurysm, with additional parameters such as aneurysm shape, possible symptoms, family history, etc. playing a role as well. Undoubtedly, there are other factors yet unknown, and many are being investigated. For the time being, we can only speak in terms of probabilities. For example, one can say that a 4 mm ophthalmic aneurysm has a rupture rate well below 1% per year, whereas the same size aneurysm located on the posterior communicating artery or basilar artery has a rupture risk of perhaps 1-2% per year. One can never say that a given aneurysm will never rupture or will rupture for sure.
What do all these statistics mean?
To make an informed decision, the patient needs to appreciate that everything has a certain risk. Living with an aneurysm has its risks. Treating aneurysms also has risks. What needs to be decided, on individual basis, is which makes more sense: treatment or observation. Is the risk of treatment justified by the risk of disease? For example, we may recommend that a small aneurysm in a one patient be observed (not treated) if we feel that treatment is more likely to harm the patient than the risk of the aneurysm rupturing over the patient’s projected lifetime. On the other hand, we may advise treatment of the same size aneurysm in a younger patient who has a greater life expectancy and therefore a greater cumulative risk of rupture. Usually, patients need time to do their research and come to their conclusion about what they wish to do. Many factors form the basis of patient-doctor discussions, which we hold with patients referred for aneurysm evaluation.
How are aneurysms evaluated?
This depends on several factors. Ruptured aneurysms are dealt with in hospital settings with an array of imaging and treatment modalities which include CT, MR, and catheter angiography; treatment options include surgery and catheter-based (endovascular) treatment. Unruptured aneurysms-which are usually discovered by MRI (or CT) – may require more diagnostic imaging, such as catheter cerebral angiography before a management decision is made. For more information, you can visit the Brain Cerebral Angiography page.
The two main options are endovascular treatment (which is performed through catheters inserted into arteries under x-ray guidance) and open surgery. Which option is best depends on many factors: aneurysm location, size, patient condition, patient preference, and local expertise. This decision has to be made on an individual basis. Endovascular (catheter-based) treatments continue to evolve so that more and more aneurysms are now amenable to durable treatment. On the other hand, certain aneurysms are still best treated with open surgery.
The first reasonably effective and safe endovascular treatment of brain aneurysms was developed in the late 1980’s. A catheter is introduced into an artery leading toward the aneurysm, similar to how it is done during Cerebral Angiography. A smaller catheter or a series of catheters are then placed into the larger guidecatheter, eventually guiding the tip of a microcatheter into the aneurysm itself. Through this catheter, detachable metal coils of appropriate size and shape are delivered into the aneurysm, gradually filling the aneurysm volume. As the coils fill the aneurysm, blood can no longer circulate in the aneurysm freely, and eventually thromboses (clots). The combination of coils and thrombus forms a plug which prevents blood from going into the aneurysm, and protects the aneurysm from rupture. Depending on the shape of the aneurysm, the coils may have a hard time staying inside. When this happens, other devices can be used to help them stay there. In the example below, a temporary balloon is inflated in the artery from which the aneurysm arises, keeping the coils from “prolapsing” out of the aneurysm until a stable configuration is achieved. The saccular aneurysm shown above was treated in this way:
During treatment, a balloon was temporarily inflated to keep help keep coils within the aneurysm sac:
The final result looks like this:
Intravascular stents, such as the Neuroform® stent, developed at NYU, can also help keep the coils effectively inside the aneurysm dome, as in this case of a patient with stable Neuroform®-coil aneurysm occlusion:
Despite advances in coil technology and devices like the Neuroform®, many aneurysms can not be adequately treated by coil embolization. The aneurysms are rarely perfect spheres with short necks, the way they are frequently drawn in cartoons and diagrams. Real aneurysms are complex, with irregular necks, and frequent underlying dysplasia of the artery from which the aneurysm arises. Although coils can be successfully placed into most of such aneurysms, the result is not perfect. Part of the aneurysm, especially at the bottom (neck) area, remains free from coils. This remnant is likely to continue growing, so that the aneurysm remains partially open and unprotected, sometimes requiring re-coiling, which usually leads to yet another recurrence. Some of these aneurysm go on to rupture, defeating the original point of treatment, while others eventually grow large enough to begin pressing on adjacent brain and nerves, producing symptoms such as double vision, vision loss, pain, unsteady gait, and others. For example, this patient was referred for treatment of a large, recurrent ophthalmic aneurysm when it grew large enough to press on the optic nerve, leading to partial blindness and difficulty with balance. Surrounding an area of recurrence is large mass of coils, outlining the true size of this aneurysm:
To address these issues, the next generation of aneurysm treatment devices, exemplified by the Pipeline Embolization Device developed at NYU by the current section chief Dr. Peter Kim Nelson, were developed. The Pipeline device was approved by the FDA for use in the United States based on results of a highly effective PUFS trial, with NYULMC’s Dr. Tibor Becske as its principal investigator. These are stent-like implants, albeit with much higher metal “coverage” than traditional stents such as the Neuroform. Placement of a Pipeline or a series of Pipelines across the aneurysm neck redirects blood flow away from the aneurysm while preserving important branch vessels which often arise near the aneurysm. Over time, the aneurysm fills with clot and is ultimately completely separated from its artery by important cells which line the inside of normal arteries and gradually grow over the scaffold of the Pipeline device. Once this happens, the aneurysm shrinks, often allowing for recovery in patients who experienced symptoms related to its pressure on adjacent brain or nerves, illustrated by Pipeline treatment of the above case:
Three months later, the recurrent part of the aneurysm is no longer visualized, and patient’s symptoms have remarkably improved:
Another example of a patient with a large cavernous segment aneurysm, coming to medical attention as a result of double vision.
Multiple Pipeline devices were placed across the aneruysm neck. The immediate post-embolization image shows stagnation of contrast material in the aneurysm, a sign of successful “flow diversion”
Six months later, the aneurysm is gone.
Despite being the most significant advance in aneurysm treatment since introduction of the detachable coil, the Pipeline device has its limitations – in particular, because of the antiplatelet medications necessary for its implantation (usually Aspirin and Plavix), the device is not a good choice for most patients with ruptured aneurysms, which continue to be treated either by coil-based embolization or by open brain surgery.
Open surgery (Clipping)
There is a great deal of variation in treatment practices, particularly for aneurysms, depending on the institution. Some centers continue to clip most aneurysms, while others overwhelmingly use endovascular methods. At NYULMC, the center for endovascular innovation, we believe that some aneurysms are still best treated by open surgery – for example, the family of Middle Cerebral Artery aneurysms, as well as many posterior and anterior communicating artery types, are more definitively and immediately addressed with surgery. Surgery involves removing part of the skull, carefully navigating to the aneurysm using a surgical microscope, and placing one or more aneurysm clips – (spring-activated blades of various sizes and shapes) across the aneurysm neck to pinch it off from its parent artery, allowing for immediate aneurysm protection. Needless to say, aneurysm clipping (like embolization) is a complex undertaking that is best performed by a neurovascular surgeon with extensive experience in dealing with all manner of issues that can arise during this kind of delicate surgery. Even though surgery involves opening the head and relatively long recovery times, the advantages of definitive immediate protection (in the right hands) are sometimes felt to be worth the disadvantages of traditional surgery.
How do I know which treatment is appropriate?
Frankly, you have to trust your doctors to give you their honest advice, understand your own preferences and motives behind them, and trust your intuition. Whatever treatment is ultimately chosen, it is critical for the patient and family to have faith in the goodwill and ability of the treating physician: endovascular or open surgeon.
For unruptured aneurysms, recovery typically takes days to weeks depending on treatment modality, procedure success, etc. Endovascular treatments are associated with significantly shorter recovery times, in general. Ruptured aneurysms require prolonged hospitalization in intensive care units and typically protracted recovery in various rehabilitation settings. Most patients continue to be periodically monitored for durability of treatment and possible new aneurysm emergence with various imaging modalities.
What do to?
While a great deal can be said about aneurysms in general, it is truly impossible to make online discussion relevant to the individual patient with his or her particular situation. The only way to meaningfully inform the patient is by direct conversation and review of imaging studies.
As Interventional Neuroradiologists, we are involved in all aspects of aneurysm diagnosis and treatment. To contact the section or make an appointment, please use the general section number 212-263-6008