If you Googled “how fast do brain aneurysms grow,” you probably want a straight answer like:
“About the speed of a houseplant.” Or “like a balloon in a toddler’s hands.” The real answer is
both less dramatic and more complicated: many brain aneurysms don’t measurably grow for years,
while a smaller group can enlarge over timeand growth matters because it’s linked with higher rupture risk.
This article breaks down what research actually suggests about aneurysm growth rate, why growth is so variable,
what symptoms to watch for (most unruptured aneurysms are quiet), and how clinicians typically think about
monitoring vs. treating. No scare tacticsjust real-world context, with a dash of humor so your brain doesn’t
feel like it’s reading stereo instructions.
First, what exactly is a “brain aneurysm”?
A brain aneurysm (also called a cerebral or intracranial aneurysm) is a bulge or ballooning
in a weakened area of a brain artery. Most are small, and many are discovered by accident during imaging for
other reasons. That “other reason” is often headachesironically, most chronic headaches are not caused by an aneurysm.
Unruptured vs. ruptured: two very different situations
- Unruptured aneurysm: Often has no symptoms. The main “job” is risk assessment and deciding whether to monitor or treat.
- Ruptured aneurysm: A medical emergency that typically causes sudden, severe symptoms (especially a thunderclap headache).
So… how fast do brain aneurysms grow?
Here’s the honest headline: there is no single growth speed. Aneurysms can be stable for a long time,
grow slowly, grow in spurts, or change shape (not just size). Researchers measure growth in different ways
(millimeters, volume, “any measurable change”), which is why you’ll see a range of numbers in studies.
What studies suggest about growth frequency
Many unruptured intracranial aneurysms (UIAs) remain stable. But measurable growth is not rare.
Large reviews and guideline-style discussions often describe growth as something like:
a minority over a few years, and more over very long time horizons.
-
Some clinical reviews report aneurysm growth observed in roughly the teens percentage range
over about 2–3 years of follow-up in certain cohorts (depending on who’s being followed and how growth is defined). -
Meta-analytic work has estimated that, across studies, the overall growth occurrence may be around a few percent per year,
with higher odds in higher-risk aneurysms (more on that below).
What about “mm per year” growth rate?
When people ask “how many millimeters per year,” they’re hoping for a tidy number. Real life doesn’t always cooperate.
Still, research offers a few useful anchors:
-
Some modeling and observational work has suggested an average growth estimate on the order of
fractions of a millimeter per year in certain assumptions and datasets. -
Other studies highlight that aneurysms that later rupture may show faster growth than aneurysms that remain unruptured,
and that the “median” growth rate for stable aneurysms can be quite small.
Translation into normal human language: many aneurysms grow slowly enough that you won’t “feel” anything happening,
and growth is typically detected only by follow-up imaging (CTA, MRA, sometimes angiography).
A key point: growth can be “size” OR “shape”
Growth isn’t only about a bigger number in millimeters. Clinicians also care about morphologythings like
irregular shape, lobulation, or a “daughter sac” appearancebecause these features can signal instability even if
overall size changes only slightly.
Why do some aneurysms grow while others stay put?
Think of aneurysm growth like a pothole in a road. Some potholes just sit there for years; others expand quickly after
freeze-thaw cycles and heavy traffic. For aneurysms, “traffic” includes blood flow forces, vessel wall health,
inflammation, and your risk-factor “weather.”
Risk factors linked with aneurysm growth
Research repeatedly associates higher growth likelihood with a mix of aneurysm features and patient factors, such as:
- Larger aneurysm size at diagnosis
- Posterior circulation or certain higher-risk locations
- Irregular shape (lobulation, blebs/daughter sac)
- Smoking (current smoking is a big one)
- High blood pressure (hypertension)
- Female sex in some datasets
- Multiple aneurysms or certain family-history contexts
Important nuance: these are risk associations, not destiny. People without obvious risk factors can still have aneurysms,
and people with risk factors can still have stable aneurysms for years.
Does growth automatically mean an aneurysm will rupture?
Not automaticallybut growth is a serious signal. In multiple research discussions and guidelines, aneurysm growth is treated as
an “instability marker” that may shift management toward treatment or closer surveillance.
Why growth changes the conversation
When an aneurysm enlarges (or changes shape), the risk profile can change meaningfully. One reason:
larger aneurysms, certain locations, and irregular shapes are linked with higher rupture riskand growth can move an aneurysm into
a riskier category.
Some cohort research has also looked at what happens after growth is detected and found that
the period after documented growth can carry a higher short-term rupture risk compared with aneurysms that remain stable.
This is why follow-up imaging isn’t “busywork”it can directly change management.
What symptoms do brain aneurysms cause?
Most aneurysms are silent until they become large, press on nearby nerves, leak, or rupture.
That silence can be unnerving, but it’s also why many aneurysms are found incidentally.
Symptoms of an unruptured brain aneurysm
An unruptured aneurysm may cause symptoms if it presses on brain tissue or nerves, especially near the eyes.
Potential symptoms can include:
- Pain above/behind one eye
- Vision changes (blurred or double vision)
- A drooping eyelid
- A dilated pupil or changes in pupil size
- Numbness or weakness on one side of the face (less common)
- Headache (sometimes, but chronic headaches are usually from other causes)
If you have new neurologic symptomsespecially sudden vision changes, drooping eyelid, or unusual one-sided facial symptomsdon’t “wait it out.”
Get medical evaluation.
Symptoms of a leaking or ruptured aneurysm (medical emergency)
A rupture classically causes a sudden, severe headache that peaks fastoften described as the worst headache of someone’s life.
Other emergency symptoms may include:
- Sudden severe headache (thunderclap headache)
- Nausea and vomiting
- Stiff neck
- Sensitivity to light
- Confusion, fainting, or loss of consciousness
- Seizure
Call emergency services immediately if these symptoms occur. This isn’t a “take two ibuprofen and see how you feel” moment.
How do doctors estimate risk and decide on monitoring vs. treatment?
Management is individualized. Clinicians weigh aneurysm size, location, shape, patient age and health, family history,
smoking status, blood pressure control, and whether symptoms are present.
Risk tools you might hear about: PHASES and friends
You may see scoring tools like PHASES (estimates 5-year rupture risk using factors such as population, hypertension, age, size, earlier SAH, and location).
Some approaches also consider tools focused on growth prediction (for example, ELAPSS-style frameworks in clinical literature), plus imaging features like irregular shape.
These tools are not crystal balls. They’re more like weather forecasts: helpful for planning, imperfect for predicting
the exact day it will rain.
Typical monitoring approach (watchful waiting)
For aneurysms judged lower-risk, clinicians often recommend periodic imaging to check for growth or shape change.
There isn’t one universal schedule for everyone; follow-up timing depends on aneurysm size, location, risk factors,
and the imaging method used. Many guidelines emphasize that intermittent imaging should be part of conservative management.
When treatment is more likely to be recommended
Treatment (endovascular options like coiling/flow diversion or surgical clipping) is more often considered when:
- The aneurysm is larger or in a higher-risk location
- There is documented growth or new irregular features
- The aneurysm is causing symptoms (for example, nerve compression)
- Risk factors are significant (e.g., uncontrolled hypertension, active smoking, strong family history)
The decision balances rupture risk against procedure risks. That balance is why you’ll see different recommendations for different people,
even with aneurysms of similar size.
Can you slow aneurysm growth or reduce rupture risk?
You can’t “DIY patch” an aneurysm (please don’t try), but you can influence important risk factors:
Risk-reduction moves that actually matter
- Stop smoking: Smoking is strongly linked with aneurysm growth and rupture risk in multiple studies and guideline discussions.
- Control blood pressure: Hypertension is a recurring risk factor for aneurysm instability.
- Follow imaging recommendations: Growth is often silent; imaging is how you catch it early.
- Discuss family history: Strong family history may influence screening and follow-up choices.
- Ask about overall vascular health: Your clinician may consider cholesterol, diabetes, and lifestyle factors as part of the big-picture plan.
If you’ve been diagnosed with an unruptured aneurysm, the “boring” stuffblood pressure meds, smoking cessation support, follow-up scans
is actually the heroic stuff.
Quick FAQ
Do aneurysms always grow before they rupture?
No. Some rupture without prior documented growth (especially if imaging wasn’t done frequently enough to detect subtle changes).
But when growth is documented, it’s treated as a meaningful warning sign.
Can you feel an aneurysm growing?
Usually not. Most growth is detected on imaging, not by symptoms. Symptoms are more likely if the aneurysm becomes large enough
to compress nearby nerves or if it leaks/ruptures.
Are small aneurysms “safe”?
“Small” often means lower risk, not zero risk. Location, shape, smoking, blood pressure, and individual context still matter.
Many small aneurysms are monitored rather than treated, but the decision is personalized.
Conclusion
Brain aneurysm growth is usually slow and variableand many aneurysms don’t measurably grow for years.
When growth does occur, it can signal higher instability, which is why follow-up imaging is such a big deal.
Symptoms are often absent until an aneurysm is large, leaking, or ruptured, so knowing emergency warning signs
(especially sudden, severe headache) is essential. If you’re diagnosed with an unruptured aneurysm, the best next steps are
working with a specialist on a monitoring/treatment plan and tackling the risk factors you can controlespecially smoking and blood pressure.
Experiences people commonly report (and what they often wish they’d known)
The word “aneurysm” has a special talent for making a normal Tuesday feel like the season finale of a medical drama.
Many people describe a whiplash moment: they went in for imaging because of something unrelatedsinus issues, a minor head injury,
dizziness, even routine screeningand came out with a surprise finding. One of the most common experiences is a strange mix of
gratitude (“It was found”) and anxiety (“Now I know it’s there”). That emotional swing is normal.
A frequent story goes like this: after diagnosis, people notice every sensation in their head. A twinge becomes a “symptom.”
A normal tension headache turns into a full investigative podcast. Clinicians often have to remind patients that
most everyday headaches are still just everyday headachesstress, dehydration, sleep, screen time, and neck tension are powerful.
What people often find helpful is having a clear “red flag” list from their care team:
sudden thunderclap headache, fainting, seizure, sudden neurologic changes, or new vision problems.
Knowing what truly requires emergency care can reduce the constant background fear.
Another shared experience is the frustration of ambiguity about growth. People understandably ask, “How fast is mine growing?”
But because growth is often slow and imaging intervals may be months to a year, there can be long stretches with no new data.
Some describe follow-up scan day as a mini life eventlike waiting for exam resultsbecause stability is reassuring and growth
can change the plan. Many patients say the most calming sentence they heard was something like,
“It hasn’t changed, and that’s great.” (It’s not a dramatic sentence, but it’s a beautiful one.)
People who successfully reduce risk factors often describe that process as empowering. For example, smoking cessation can feel less like
a generic health recommendation and more like a targeted action: “I’m doing something that lowers my aneurysm risk.”
Blood pressure control can feel similarespecially when patients learn that consistent control matters more than occasional “good readings.”
Some build routines: checking blood pressure at home, setting reminders, walking most days, cutting back on nicotine and stimulants,
and keeping follow-up appointments like they’re non-negotiable (because, honestly, they kind of are).
Families and caregivers also report their own learning curve. Many wish they’d known that an unruptured aneurysm can be monitored safely in many cases,
and that “watchful waiting” doesn’t mean “doing nothing.” It means tracking imaging, managing risk factors, and having a plan.
When someone has symptoms from an unruptured aneurysmlike vision changes or drooping eyelidthe experience can be confusing,
because it doesn’t always match what people expect (they expect pain; sometimes it’s subtle nerve-related changes).
The best caregiver advice tends to be practical: keep a folder of scan reports, write down questions before appointments,
and don’t be shy about asking what would change the plan (growth? shape change? symptoms?).
Finally, many people say they wish they’d been told upfront that it’s okay to seek support for the mental load.
Living with “an incidental finding” can be mentally loud even when the aneurysm is physically quiet.
Anxiety doesn’t mean you’re overreacting; it means your brain is trying to protect you with the only tool it has: worry.
A clear medical plan, reliable follow-up, and support for stress (therapy, mindfulness, exercise, or support groups)
can make life feel normal againbecause the goal isn’t just a stable scan. It’s a stable you.
