Cerebral (Brain) Aneurysms

A bulge in a brain artery — most never cause problems, but treatment decisions require genuine cerebrovascular expertise.

In brief

A bulge or dilatation of a brain artery, present in 2–3% of people
Most are never noticed and never cause a problem
A rupture (subarachnoid haemorrhage) is a medical emergency
Treatment balances the lifetime risk of rupture against the risk of treatment
All cases are discussed in a multidisciplinary cerebrovascular meeting

What is an Aneurysm?

A brain aneurysm (also known as a “cerebral”, “berry” or “saccular” aneurysm) is a bulge or dilatation of an artery within the brain. These arteries are high pressure vessels surrounded by cerebrospinal fluid (CSF), which bathes your brain and is known as the subarachnoid space. There are four main arteries that supply blood to the brain, and aneurysms typically form at weak areas of one of these arteries, typically where the artery splits into two or ‘bifurcates’. Aneurysms typically become evident between the ages of 45 and 65 due to various risk factors (see below). They occur in approximately 3% of the adult population, and the vast majority are unrecognised and never cause a problem.¹ Of those people that have an aneurysm, approximately 20% will have more than one aneurysm.¹

What are the Symptoms of an Unruptured Aneurysm?

Typically, aneurysms do not cause any symptoms until they become very large or rupture. When they are large they can press on nearby structures causing symptoms such as double vision, an enlarged pupil, or weakness on one side of the face^.2When they rupture into the CSF, this is known as a subarachnoid haemorrhage (SAH). This is a very dangerous condition that requires urgent hospital treatment and repair of the aneurysm.

What are the Symptoms of a Ruptured Aneurysm (Subarachnoid Haemorrhage)?

When an aneurysm ruptures, high pressure arterial blood is released into the CSF space, known as a subarachnoid haemorrhage, or sometimes into the brain tissue itself, known as an intracerebral haemorrhage (ICH). As the blood is released, the pressure within the head suddenly increases and eventually stops as a delicate clot seals the rupture point. This sudden increase in pressure causes the symptoms typically seen: patients may transiently lose consciousness, report “the worst headache of my life”, nausea, vomiting, stiff neck and a reduced level of consciousness. Around one third of people who suffer a ruptured aneurysm will die, and a further 30–40% are left with significant disability^.2

Aneurysm Risk Factors

Certain conditions are associated with a known increased risk of aneurysm formation. The most important factors are listed below. The more of these a patient has, the higher the likelihood of treatment being offered. Importantly, stopping smoking and treating high blood pressure are the most effective ways to reduce the risk of both aneurysm formation and rupture.³

Age — increased age, especially > 50 years old
Gender — females are at increased risk (up to twice that of men after age 50)
Smoking — significant increase of both formation and rupture
Hypertension — untreated high blood pressure
Family History — two or more direct family members with an aneurysm
Connective tissue disorders — autosomal dominant polycystic kidney disease (ADPKD), vascular Ehlers-Danlos syndrome and fibromuscular dysplasia; a possible but less well-established association also exists with Marfan’s syndrome
Excessive alcohol — excessive daily alcohol intake
Drug use — especially cocaine and amphetamines

How are Cerebral Aneurysms Diagnosed?

Most cerebral aneurysms go unnoticed until they rupture or are found during medical imaging for an unrelated condition. Where a patient presents to hospital with suspicion of a subarachnoid haemorrhage, the first step is to perform imaging to confirm the diagnosis. Several tests are available:

Computed tomography (CT)

A rapid and non-invasive test using X-rays to determine if blood has leaked into the CSF space. This is combined with a contrast dye scan called CT angiography (CTA) to visualise the brain blood vessels and the location, size and shape of the aneurysm. Treatment decisions are typically made from this imaging alone.

Magnetic Resonance Imaging (MRI)

An MRI uses radio waves and a magnetic field to create brain images without radiation. Brain blood vessels can be assessed using MR angiography (MRA); however, it is much slower than CTA and is typically reserved for elective and screening cases.

Cerebral Angiography

A minimally invasive imaging technique involving a small puncture in the groin, passing a thin tube up the arteries to the brain to obtain very high quality images of the brain vasculature and aneurysm. Now typically reserved for patients with particularly complex anatomy, those undergoing endovascular treatment, or those with vasospasm as a complication of their SAH (see below).

Cerebrospinal fluid (CSF) analysis

When the initial CT does not show evidence of a brain bleed but clinical suspicion remains high of subarachnoid haemorrhage, a lumbar puncture is performed. This involves passing a small needle into the fluid cavity of the lower spine and removing a small amount of CSF for analysis.

Should an Aneurysm be Treated?

All ruptured aneurysms are urgently treated to prevent re-bleeding and worsened outcomes.

However, as most incidental aneurysms never rupture, treatment is not necessarily required. Ultimately, a person’s lifetime risk of rupture must be balanced against the risk of treatment. Averaged across all incidental aneurysms, the annual risk of rupture is low — on the order of 1% per year — though it varies considerably with aneurysm and patient characteristics.⁴ Many factors are taken into consideration:

Patient age — younger patients are more likely to be treated
Aneurysm size — often smaller aneurysms (< 5 mm) are simply monitored. Rupture risk rises steeply with size. For small aneurysms (under 7 mm), estimates range from roughly 0–0.5% per year in North American data to around 1% per year in Finnish and Japanese cohorts, rising further with risk factors such as smoking and high blood pressure. Larger aneurysms carry substantially higher annual risks, up to several percent per year for the largest.^5-7
Aneurysm location — different aneurysm locations carry different risk; posterior circulation and anterior communicating artery aneurysms carry a higher risk of rupture⁵
Aneurysm shape — irregular shape or the presence of a daughter sac is associated with higher rupture risk
Prior aneurysm rupture — prior SAH from a separate aneurysm increases overall risk
Risk of aneurysm treatment — not all aneurysms carry the same treatment risk
Patient wishes — patient anxiety and quality of life are treatment factors

To assist in estimating rupture risk, validated scoring tools such as the PHASES score (Population,
Hypertension, Age, Size of aneurysm, Earlier SAH, Site) can provide a 5-year rupture risk estimate based on individual patient and aneurysm characteristics.⁴ This is a useful aid in multidisciplinary discussion, though it does not replace the need for clinical judgement.

All patients should be discussed in a multidisciplinary meeting with a neurosurgeon, interventional neuroradiologist (INR) and sometimes a neurologist, to ensure a consensus opinion on both treatment requirement and best treatment modality.³ When treatment risk is deemed less than the lifetime risk of the aneurysm itself, treatment is typically offered.

What are the Complications of SAH?

Rebleeding. As the small clot preventing continued bleeding is extremely delicate, there is a high risk of re-rupture — reported at approximately 9–17% within the first 72 hours if left untreated, and up to 50% within the first 6 months. Mortality approximately doubles if rebleeding occurs.^8,9

Hydrocephalus. Brain pressure elevation from the SAH is often compounded by a build-up of CSF within the fluid spaces (ventricles), known as hydrocephalus. This occurs in approximately 20–30% of patients with SAH.^9,10 It is treated by placing a small rubber catheter known as an external ventricular drain (EVD) into the ventricle and diverting fluid into an attached bag. This remains in place until the brain self-regulates fluid once more; occasionally a permanent EVD is required, where the catheter is tunnelled from the brain into the abdomen, known as a ventriculo-peritoneal shunt (VPS).

Vasospasm and Delayed Cerebral Ischaemia. Blood within the subarachnoid space often causes the brain’s blood vessels to narrow, limiting blood supply to vital areas. Cerebral vasospasm typically develops 3–14 days after rupture and is a leading cause of secondary morbidity and mortality. It affects 20–45% of patients and, if severe enough, may lead to stroke and permanent disability despite optimal management.^9,10

Altered sodium levels. SAH can disrupt the sodium balance within the blood, potentially causing brain swelling and increased brain pressure.

Seizures. SAH may cause seizures either at the time of the initial bleed or in a delayed fashion. These may be clinically silent and require specialised brain monitoring (EEG) to detect them. If left uncontrolled, they may cause permanent brain damage.

How are Cerebral Aneurysms Treated?

Once the decision has been made to treat the aneurysm, there are two primary methods used to exclude the aneurysm from the brain circulation and prevent rebleeding. Some aneurysms are suitable for only one of these approaches, while others are amenable to both. Where an aneurysm is equally suitable for either, endovascular treatment is often favoured; however, each approach carries its own advantages and disadvantages, and the final decision should be made through an appropriate cerebrovascular multidisciplinary meeting (MDM) to determine the best treatment for the individual patient.^3,9 It is important the patient understands the reasons for the recommended treatment option, as well as its relative risks and benefits for their particular situation. Both methods require a general anaesthetic and aftercare in either an intensive care unit (ICU) or neurosurgical high dependency unit (HDU), depending on clinical severity. General treatment risks include deep venous thrombosis (DVT) / pulmonary embolus (PE) (1–2%), pneumonia (<1%), heart attack (<1%), adverse drug reaction (<0.1%) and death (<0.1%).[/et_pb_text][et_pb_text _builder_version="4.27.8" _module_preset="a20112d2-b606-4a5f-8bd4-abb6f7158418" hover_enabled="0" global_colors_info="{}" sticky_enabled="0"]Clipping[/et_pb_text][et_pb_text _builder_version="4.27.8" _module_preset="default" global_colors_info="{}"]

Microsurgical clipping of a cerebral aneurysm involves shaving a small amount of hair, followed by a skin incision and creating a hole in the skull known as a craniotomy. A microscope is then used to carefully expose the aneurysm and surrounding arteries. One or more alloy clips (always MRI compatible) are used to pinch off the aneurysm from the brain circulation, ensuring that the arteries leading to and from it are not narrowed or blocked. This is confirmed using a combination of visual inspection, Doppler ultrasound and intraoperative angiogram. This is a very technically demanding procedure that should only be performed by an experienced cerebrovascular neurosurgeon who regularly performs this type of surgery.

The risk of a serious complication (stroke, major neurological deficit or death) for an elective aneurysm clipping is typically 2–4%.<sup>5</sup> Other less serious complications include brain haemorrhage requiring repeat surgery (<1%), brain infection (1%), wound healing problems (1%), seizures (1–2%) and incomplete aneurysm clipping (<5%). For ruptured cases, these figures are higher — at least twice those of unruptured cases.

Whilst clipping is initially a more invasive procedure than coiling, if an aneurysm is adequately clipped it will very rarely recur and requires significantly less frequent imaging follow-up.

Link to aneurysm clipping: https://www.youtube.com/watch?v=8WSZUtC9oi0&feature=youtu.be

Endovascular treatment

Performed by either an interventional neuroradiologist (INR) or INR-trained neurosurgeon, this is a less invasive treatment whereby a small catheter is inserted into the groin and guided up into the brain vessels using live X-ray imaging. Often referred to as “coiling”, one established method packs the aneurysm with small platinum coils. Increasingly, intrasaccular devices — small braided baskets placed within the aneurysm sac (such as the WEB or Artisse devices) — are used, as are stents and flow diverters (alloy mesh sleeves) placed across the aneurysm neck.³ These devices promote clot formation within the aneurysm, blocking it from the main arterial circulation.

The major risks of endovascular treatment are comparable to those of clipping, with serious complication (stroke, major neurological deficit or death) rates of approximately 2–4%.³ Blood-thinning agents such as aspirin and/or clopidogrel are often needed for a period of 3–12 months. Less serious risks include contrast reaction affecting kidney function and access-site complications in the groin. A rare but specific complication is contrast-induced encephalopathy — a temporary disturbance of brain function caused by a reaction to the contrast dye, which may produce confusion, visual disturbance (including temporary blindness), weakness or seizures; it usually resolves completely within a few days.¹¹

Aneurysm recurrence, though rarely presenting with rebleeding, is more common with this technique and occasionally requires retreatment. Imaging follow-up is therefore more frequent than after clipping.

Link to aneurysm coiling: https://www.youtube.com/watch?v=5Ss-IOmFyeA&feature=youtu.be

Aneurysm Screening

Patients are typically recommended for screening when two or more first-degree relatives (i.e., child, sibling or parent) are known to have an aneurysm (either incidental or ruptured). If only one such relative exists, screening may also be offered if they had multiple aneurysms, or if the patient has multiple additional risk factors. Patients with autosomal dominant polycystic kidney disease (ADPKD) are also candidates for aneurysm screening given their significantly elevated prevalence.³

References

Helpful links

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Cerebral Aneurysms — patient information sheet PDF · prepared by Mr Jeremy Russell

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Content on this page is for education and information only and is not a substitute for advice from your doctor. Medically reviewed by Mr Jeremy Russell.