The word aneurysm means a dilatation, or widening, of a blood vessel. Berry aneurysms, also known as saccular aneurysms, are balloon-like outpouchings of an artery in the brain. The wall of the artery is weak in these aneurysms, which means that under certain conditions, like high blood pressure (hypertension), the vessel wall can break and allow blood to flow into the subarachnoid space between the arachnoid mater and dura mater. This bleeding, known as a subarachnoid hemorrhage, can lead to death or severe disability.
That said, many people have berry aneurysms that don’t rupture. Autopsies done on people who died of various causes found that about 5% of people have such an aneurysm. However, in actual practice, most aneurysms are discovered after something happens, like a subarachnoid hemorrhage, which leads physicians to look for a cause.
After a subarachnoid hemorrhage, there is a significant risk of rebleeding from the ruptured site. Such bleeds carry an even higher mortality. About 70% of people die from aneurysmal rebleeds. For this reason, such aneurysms cannot just be left alone. Surgical or vascular intervention is necessary.
Which Aneurysms Require Treatment?
There is no question that a ruptured berry aneurysm requires treatment, and the sooner, the better. The risk of rebleeding is highest shortly after the initial subarachnoid hemorrhage.
But what if an imaging test like an MRI shows an aneurysm that has not ruptured? Is a neurosurgical procedure still required? The answer depends on certain characteristics of the aneurysm.
- Size: Larger aneurysms are more likely to rupture. However, there’s some debate over just how large an aneurysm should be in order to recommend an intervention like surgery. One large study that often guides treatment has suggested a cutoff of 7 millimeters.
- Location: Aneurysms in the arteries at the back of the brain are less common overall, but have a higher risk of rupture than aneurysms at the front of the brain.
- Previous subarachnoid hemorrhage: The higher risk of bleeding in someone who has already had a bleed from a separate aneurysm may indicate abnormally weak blood vessels overall.
- Family history: Similarly, people with a family history of aneurysms tend to have ruptures at younger ages and at smaller aneurysm sizes, perhaps because of inherited blood vessel weakness.
Whether or not an intervention is deemed necessary will depend on a combination of all of the factors above. There are two main options for such an intervention.
Neurosurgical Aneurysm Repair
Since many cerebral aneurysms dangle off the main vessel like a balloon, they can be isolated from the rest of the vessel by putting a metal clip across the neck of the aneurysm.
In this procedure, the skull is opened to allow a neurosurgeon to access the brain and find their way to the blood vessel. Despite the seriousness of such an operation, in one study, just over 94% of patients had a good surgical outcome. As is usually the case, the likelihood of a better outcome is higher if the surgeons and additional staff are very experienced with the procedure.
Possible risks of the procedure include further brain damage or bleeding. However, these risks are generally outweighed by the potentially devastating consequences of a subarachnoid hemorrhage.
Endovascular Aneurysm Repair
In the early 1990s, a device was introduced that allowed a thin catheter to weave through the blood vessels of the body up to the site of an aneurysm, where platinum coils were inserted into the sac of the aneurysm. Clots formed around these coils, thereby sealing the aneurysm off from the rest of the body. This interventional radiological technique is commonly referred to as “coiling,” although as time has passed, other methods of sealing off aneurysms, such as polymers, have also come into practice.
In general, the results of endovascular aneurysm repair seem comparable to more traditional neurosurgical clipping techniques, but this varies. In one study, coiling was associated with better outcomes in the back of the brain, and clipping was better in the front. The size and the shape of the aneurysm can also limit options for treatment, since a wide neck or large aneurysm may not respond well to coiling.
Other factors, such as the severity of the subarachnoid hemorrhage and overall health and age of the patient, may also play a role in deciding how to treat an aneurysm. Perhaps the most important factor in deciding whether to clip or coil an aneurysm is the skill and experience of the practitioners who would be doing the procedure.
Broderick JP, Brown RD Jr, Sauerbeck L, et al. Greater rupture risk for familial as compared to sporadic unruptured intracranial aneurysms. Stroke 2009; 40:1952.
McLaughlin N, Bojanowski MW. Early surgery-related complications after aneurysm clip placement: an analysis of causes and patient outcomes. J Neurosurg 2004; 101:600.
Wiebers DO, Whisnant JP, Huston J 3rd, et al. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 2003; 362:103.