How Often Should an Untreated Brain Aneurysm Be Scanned?

If your unruptured brain aneurysm is being managed without preventive treatment—a strategy sometimes called “watchful waiting” or “active observation”—you will need regular imaging scans to monitor it for any changes. Observation is an active risk-management choice, carefully balancing the estimated risk of the aneurysm rupturing against the risks of a surgical or endovascular procedure.

There is no single, universal timetable for these scans. For example, guidelines from the European Stroke Organisation suggest radiological monitoring to check for growth, but they acknowledge this is based on limited evidence and do not mandate a strict schedule ^[1]. Instead, your doctor will customize your imaging intervals based on your specific aneurysm and overall health.

🚨 Emergency Warning: When Not to Wait for Your Next Scan

Do not wait for your scheduled scan if you experience signs of a ruptured aneurysm. Call emergency services (like 911) immediately if you develop:

• A sudden, severe, “worst-ever” headache
• Neck stiffness
• Nausea and repeated vomiting
• Fainting, collapse, or a seizure
• New weakness, numbness, or trouble speaking or seeing

These symptoms require immediate emergency evaluation.

Illustrative Monitoring Timeline

While your schedule will be individualized, many neurovascular specialists follow a common pattern ^[2]:

• First Follow-Up (6 to 12 months): Your first follow-up scan typically occurs 6 to 12 months after your initial diagnostic scan ^[3]. This early check ensures the aneurysm is not growing rapidly.
• Ongoing Surveillance (Every 1 to 3+ years): If the first follow-up shows the aneurysm is stable, your doctor may extend the time between future scans ^[2]. For selected, very small, low-risk aneurysms, some models suggest an interval of up to 5 years may be appropriate ^[4].

Note: Never change or skip a scheduled scan without consulting your care team. If a scan is delayed due to scheduling issues and you are feeling anxious, contact your doctor’s office to discuss the safest timeframe.

What Determines Your Specific Schedule?

Your care team decides how often you need scans based on the likelihood of the aneurysm growing. Doctors sometimes use tools like the ELAPSS score to help estimate this growth risk ^[5]. ELAPSS stands for Earlier subarachnoid hemorrhage (prior bleeding around the brain), Location, Age, Population, Size, and Shape ^[6]. It is a helpful guide, but your doctor’s clinical judgment sets the final plan.

Factors that influence your risk and your imaging schedule include:

• Size, Location, and Shape: Aneurysms that are larger, located in the posterior circulation (the arteries at the back of the brain), or have irregular shapes or blebs (blister-like bumps) generally require closer monitoring or a discussion about preventive treatment ^[7][8].
• Prior Imaging and Growth: Confirmed growth usually prompts a discussion about switching from observation to preventive treatment. In one large study of conservatively managed aneurysms, those that grew had an estimated cumulative rupture risk of 4.3% at 1 year and 6.0% at 2 years after the growth was detected ^[8]. However, this risk varies heavily depending on size, shape, and location. Furthermore, a tiny change of 1 millimeter on a scan can sometimes just be measurement error rather than true growth ^[9]. Your doctor may order a repeat or higher-resolution scan to confirm any suspected changes before making a treatment decision.
• Your Health and History: Managing your blood pressure and quitting smoking are actionable steps you can take to lower your overall risk of aneurysm growth ^[10]. A history of a previous aneurysm rupture or genetic conditions like ADPKD (autosomal dominant polycystic kidney disease) also inform your overall risk and may lead to more frequent scans ^[11]. If you have a family history of brain aneurysms, discuss with your doctor whether other family members should be screened.

Which Scan Will Be Used?

Your doctor will choose an imaging method based on your anatomy, medical history, and safety factors. To make accurate comparisons over time, it is best to consistently use the same type of scan and measurement technique ^[12].

• MRA (Magnetic Resonance Angiography): MRA uses magnets and radio waves, avoiding ionizing radiation (energy that can damage cells over time with high exposure). It is often preferred for long-term monitoring, though it can sometimes have artifacts related to blood flow that make very small aneurysms harder to measure ^[13][2]. If you have a pacemaker or metallic implants, tell your doctor; while many modern pacemakers are “MRI-conditional” and can be safely scanned under specific protocols, some cannot.
• CTA (Computed Tomography Angiography): CTA uses X-rays and an injected iodine-based contrast dye to create fast, high-resolution images of blood vessels ^[14]. Your doctor will consider the cumulative radiation exposure, your kidney function, any prior allergies to contrast dye, and pregnancy status before recommending a CTA.
• DSA (Digital Subtraction Angiography): DSA is considered the gold standard (the most accurate benchmark test) for showing detailed blood vessel anatomy. However, it is an invasive procedure requiring a catheter threaded through your arteries, which carries small but real risks of stroke, bleeding, or arterial injury ^[15]. It is generally reserved for clarifying uncertain noninvasive scans or detailed planning right before a treatment procedure, rather than for routine surveillance.

How Long Will Monitoring Continue?

For many people, surveillance imaging is a lifelong process, as even aneurysms that have been stable for years can eventually begin to grow ^[2][16].

However, your doctor may recommend stopping surveillance if your overall health or life expectancy changes ^[17]. Because the goal of monitoring is to detect growth so the aneurysm can be treated, scanning may no longer be useful if advanced age or severe health conditions mean that the risks of a preventive procedure (such as surgical clipping or endovascular coiling) would outweigh the benefits ^[18].