Aneurysm of a cerebral artery

An aneurysm is a balloon-like enlargement of an artery in the brain. It occurs when the vessel wall is weaker in one area and bulges outward.

There can be various reasons for this:

• Congenital weaknesses in the vessel wall
• Risk factors such as high blood pressure, smoking, or family history
• Changes in the vessels over the course of a lifetime, for example due to wear and tear

Most aneurysms cause no symptoms and therefore go unnoticed. They are often discovered by chance during an examination.

An aneurysm becomes dangerous when it ruptures. This can cause sudden and severe bleeding in the brain—a life-threatening emergency.

Ruptured aneurysm and subarachnoid hemorrhage

Approximately 2% of the population has an aneurysm in the brain, which is often discovered by chance. This figure has been confirmed in several large-scale analyses of angiograms—for example, in a study that evaluated brain MRI images of healthy adults *.

Sometimes higher frequencies of up to 6% are reported. However, these are mostly based on autopsies, in which the advanced age of the individuals examined and the detection of even the smallest vascular irregularities skew the figures upwards. For the general population, therefore, around two in every hundred people have an aneurysm, usually without knowing it.

If an aneurysm is discovered incidentally, in most cases we recommend a consultation with one of our specialist neurosurgeons or neuroradiologists. At the neurosurgery clinic at Inselspital, we offer detailed consultations during the aneurysm consultation hours with Prof. Andreas Raabe or Prof. David Bervini.

Interdisciplinary assessment: The findings and medical history are then usually discussed together in the weekly aneurysm board meeting.

Follow-up: In most cases, the board initially recommends regular check-ups.

Treatment in case of risk: If there are clear risk factors for the aneurysm rupturing, we recommend treatment.

The decision is always made on an individual basis. Follow-up checks and possible treatments are carefully weighed up together with the patient. Personal attitude also plays an important role: some people prefer to live with the low risk of rupture, while others prefer the one-time risk of treatment.

In most cases, we recommend an annual follow-up examination using MRI without contrast agent. Even if an aneurysm remains stable for years, there is always a certain risk that it will grow.

However, the frequency of follow-up examinations is adjusted individually, depending on the patient's age and the size and shape of the aneurysm. The optimal calculation of follow-up intervals is a current research topic in neurosurgery and neuroradiology at Inselspital

If an aneurysm in the head ruptures, it is life-threatening:

• Approximately 30% of those affected die from the bleeding or its consequences.
• Less than 20% survive without permanent damage.

This raises an important question: Should an aneurysm be treated preventively before it ruptures? The answer depends on whether the risk of rupture is higher than the risk of treatment.

Studies show:

• Small (<7 mm) aneurysms in the anterior circulation that are discovered by chance have a very low risk of bleeding of about 0.2% per year.
• Other aneurysms, on the other hand, can have a risk of over 10% per year.

It must therefore be carefully considered whether regular monitoring or treatment is more beneficial.

You can find more information on ruptured aneurysms and cerebral hemorrhages on the page Ruptured aneurysm and subarachnoid hemorrhage.

The following factors—individually or in combination—can increase the risk of bleeding and thus influence the decision to treat. If there are no risk factors, the risk of bleeding is less than 0.2 % per year.

The goal of treating a brain aneurysm is to completely and permanently isolate the aneurysm from the bloodstream in order to prevent rupture and cerebral hemorrhage.

There are two different treatment techniques available for this purpose:

Clipping (microsurgical procedure)

• The aneurysm is closed off by means of a minor surgical procedure.
• This treatment is performed in neurosurgery.

Coiling (endovascular procedure)

• The aneurysm is closed off via the blood vessels using a catheter.
• This treatment is performed in interventional neuroradiology.

During clipping, the aneurysm is accessed via a small incision in the skin and a targeted opening in the skull in order to achieve an optimal cosmetic result. The access route is chosen so as to minimize stress on the brain.

• The surgical microscope provides high magnification and excellent lighting, allowing the vessels near the aneurysm to be identified and preserved.
• Modern techniques such as intraoperative infrared angiography *, electrophysiological monitoring, or vascular navigation increase safety and reduce stress for the patient.
• In the case of large or complex aneurysms, additional procedures are sometimes used, e.g., bypass (blood diversion), trapping (exclusion), or wrapping (redirection).

• High closure rate of the aneurysm
• In most cases, no further follow-up examinations are necessary

The most common serious complications of clipping are:

• severe secondary bleeding
• permanent epilepsy
• vascular occlusion resulting in stroke

These risks add up to approximately 2%.

Approximately 97% of all aneurysms that have been carefully planned for surgery can be eliminated.

In rare cases, unforeseeable findings such as small important vessels, calcifications, or wall thickening may necessitate a switch to endovascular treatment. At our center, we always strive for maximum safety with minimal risk.

Follow-up examinations after clipping are rarely necessary. Only about 5% of patients require further observation due to small remnants, and only 1% require follow-up treatment.

The procedure is performed under general anesthesia. The catheter is usually advanced through the groin artery (femoral artery) to the cerebral arteries.

• Contrast medium and X-ray fluoroscopy allow the vessels and instruments to be tracked precisely.
• Depending on the shape and size of the aneurysm, additional aids such as a balloon or a stent may be necessary to place the coils securely.

• Minimally invasive: No major incisions in the skin or bone of the head are necessary, as access is gained via a blood vessel.
• Short recovery time: Patients are often able to resume normal activities more quickly than after open surgery.
• Wide range of treatments: Modern techniques (e.g., balloon or stent support, flow diverters) can also be used to treat more complex aneurysms.

Serious complications are rare. They occur in about 2% of treatments overall.

Possible risks include:

• Injury to the aneurysm by the coil or wire, resulting in bleeding
• Vascular occlusion, which can lead to a stroke
• Allergic reaction to the contrast agent used

After endovascular treatment, around 20% of aneurysms show a small residual or renewed blood flow over time. We therefore recommend regular follow-up checks:

• after 6 months
• after 24 months
• with magnetic resonance imaging or angiography if necessary

Repeat treatment after endovascular therapy is necessary in around 10% of aneurysms. If unexpected difficulties arise during the procedure, it may be necessary to switch to surgery. Here too, our center always applies the principle of choosing the treatment with the lowest risk.

Today, there is no longer any competition between surgery (clipping) and catheter treatment (coiling). Both procedures have their strengths and are used where they promise the best results.

• Clipping is technically easier for many unruptured (non-burst) aneurysms and offers a very permanent solution.
• Coiling is often less invasive for the same level of difficulty, as access is via the vessels and no surgery on the head is necessary.

In the case of an aneurysm, aneurysm-specific factors and patient-specific factors must be weighed against each other in order to determine the optimal treatment strategy for the individual patient. Rare special forms such as giant aneurysms carry a significantly higher risk and require particularly careful consideration. The decision is always made jointly by an interdisciplinary team of neurosurgeons and neuroradiologists.

In the case of an intracranial aneurysm, various factors must be taken into account and weighed against each other in order to determine the optimal treatment strategy for the individual patient.

The risk of complications depends heavily on the size of the aneurysm.

• Clipping: The larger the aneurysm, the higher the risk of complications.
• Coiling: Success and occlusion rates are lower for very large aneurysms.
• Very small aneurysms (< 2 mm): Coiling is technically difficult in these cases because the aneurysm sac cannot be reliably filled with coils. In such cases, additional aids such as stents or balloons often have to be used.
• Medium-sized aneurysms: Many can be successfully closed endovascularly.

The location of the aneurysm in the brain plays an important role in choosing between clipping and coiling. It influences the safety and success rate of both procedures:

• Posterior cerebral vessels (e.g., basilar artery):
  • Surgery is technically more difficult and associated with a higher risk in these cases. *, *
  • Endovascular therapy is usually gentler and more suitable in these cases.
• Middle cerebral artery (arteria cerebri media, especially at the bifurcation):
  • These aneurysms often have a wide base and vessels branching off directly from the neck of the aneurysm. They are therefore more frequently clipped.
  • Endovascular treatment is possible, but often requires additional aids such as stents or balloons, which increases the risk of reopening (recanalisation) or complications.

Most aneurysms can be treated safely with clipping or coiling. However, there are rare special types that pose a challenge for both methods:

• Giant aneurysms (> 2.5 cm)
• Partially calcified aneurysms
• Partially thrombosed aneurysms (already partially filled with blood clots)

Coiling: Complete, stable occlusion is often difficult to achieve in partially thrombosed aneurysms.

Clipping: If the neck of the aneurysm is easily accessible, a clip can be a good solution. However, calcifications in the neck area can make clipping difficult or impossible.

So-called flow diverters are special stents that have expanded the possibilities of endovascular treatment in recent years. They are mainly used in large vessels supplying the brain. Their fine mesh structure redirects the blood flow in such a way that the aneurysm is gradually closed. This means that even aneurysms that were previously considered difficult or impossible to treat can now be treated.

Several studies have shown that older patients are more likely to benefit from less invasive endovascular therapy, as it is less physically demanding. A subgroup analysis of the ISAT study shows an increased rate of disability or death in older patients with ruptured intracranial aneurysms (43.9% vs. 39.9%) when directly comparing the microsurgical treatment group with the endovascular treatment group *.

In younger patients, especially those with incidentally diagnosed, unruptured aneurysms, surgery (clipping) may have advantages because it offers a better long-term occlusion rate and complications are less common overall.

Patients with serious pre-existing conditions are usually treated endovascularly to reduce the risk of surgery.

Endovascular therapy is also often the better choice after severe subarachnoid hemorrhage with poor clinical neurological status or vascular spasms (vasospasms).

If an aneurysm bleed causes a large hematoma (blood clot), it is removed surgically as an emergency procedure. The aneurysm can be clipped directly during the same operation.

When treating aneurysms, it is not only the choice between surgery (clipping) and catheter treatment (coiling) that is crucial, but also the experience of the treatment team.

Studies clearly show:

• In highly specialized centers with a large number of cases («high-volume centers»), complication rates are significantly lower *
• Experienced neurosurgeons and interventional neuroradiologists achieve better results – both for ruptured and unruptured aneurysms.

It is therefore recommended that aneurysms be treated at a supra-regional neurovascular center wherever possible, where the necessary expertise and experience are concentrated.