Brain Aneurysms — Clipping & Coiling

The Basics

What Is a Brain Aneurysm?

A weak spot in a blood vessel wall that balloons outward under normal blood pressure.

Arteries carry blood under constant pressure with every heartbeat. Most artery walls are strong enough to handle this for a lifetime, but at certain points, usually where a vessel branches, the wall can be thinner or weaker than it should be. Over years, that weak spot slowly balloons outward into a thin-walled sac called an aneurysm. Most brain aneurysms form at the base of the brain, in and around a ring of connected arteries called the Circle of Willis at bifurcation points. The most common aneurysm locations include the anterior communicating artery, posterior communicating artery, middle cerebral artery, and basilar artery.

Most aneurysms are small, round ("saccular") outpouchings with a narrow neck connecting them to the parent artery; a smaller number are longer, spindle-shaped ("fusiform") widenings of the vessel itself. An aneurysm is not a tumor and does not spread. The concern is entirely mechanical: the thin sac wall lacks the normal layered structure of a healthy artery, so it is weaker and, in some aneurysms, at risk of tearing and bleeding into the space around the brain.

Nationally, an estimated 1 in 50 adults is living with an unruptured brain aneurysm. While most of these aneurysms do not cause symptoms, they do carry a risk of rupture. Management of an aneurysm depends on the symptoms and presentation, patient characteristics, and aneurysm size and location. Brown Neurosurgery's cerebrovascular team evaluates aneurysms found incidentally on imaging done for another reason, aneurysms found because of symptoms, and aneurysms that have already ruptured, and works with each patient to weigh the specific risk of that aneurysm against the risk of treating it.

Key Facts

How common: About 1 in 50 adults has an unruptured brain aneurysm; most never rupture.

Most common shape: Saccular ("berry") aneurysm with a narrow neck, at an artery branch point.

Most common sites: Anterior communicating, posterior communicating, and middle cerebral arteries.

Rupture risk: Averages well under 1% per year, but varies widely by size, shape, and location.

If ruptured: A subarachnoid hemorrhage (SAH) — a medical emergency requiring immediate care.

Main treatments: Surgical clipping, endovascular coiling, or flow diversion; or careful monitoring.

Symptom Response

What Symptoms Should I Be Aware Of?

Unruptured and ruptured aneurysms look almost nothing alike. Select a symptom to learn what it can mean.

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A sudden, severe "worst headache of my life" is a medical emergency

If it comes on abruptly, peaks within seconds to minutes, and feels unlike any headache you've had before, call 911 or go to the nearest emergency department immediately. This is the classic presentation of a ruptured aneurysm (subarachnoid hemorrhage), and early treatment substantially improves outcomes.

Select a symptom on the left to learn more.

Risk & Screening

Am I at Risk?

A mix of factors you can change and factors you can't both influence whether an aneurysm forms or grows.

Select a factor on the left to learn more.

Risk Calculator

Estimate Your PHASES Score

PHASES is a validated research tool that estimates the 5-year risk of rupture for an unruptured aneurysm from six routinely available factors. It is a starting point for discussion, not a stand-alone decision.

Population / region

Hypertension

Age

Aneurysm size

Earlier SAH from a different aneurysm

Aneurysm site

Worked example from the original study: a 55-year-old North American patient with no hypertension, no prior rupture, and a medium-sized (8 mm) posterior-circulation aneurysm scores 0+0+0+3+0+4 = 7 points, corresponding to about a 2.4% five-year rupture risk.

PHASES Score

0

Estimated 5-Year Rupture Risk

0.4%

Low

Based on the PHASES score (Greving et al., Lancet Neurology, 2014), derived from pooled data on 8,382 patients across six prospective cohorts. It does not account for smoking, family history, aneurysm shape, or growth on serial imaging, and is not designed to be used alone. We combine it with your full history, aneurysm morphology, and your own priorities at our multidisciplinary conference.

Treatment Options

Clipping vs. Endovascular Treatment

The right choice depends on the aneurysm's size, shape, and location, whether it has ruptured, and your overall health. Our multidisciplinary conference reviews every case.

	Surgical Clipping	Endovascular (Coiling / Flow Diversion)
What happens	A craniotomy opens the skull; a metal clip is placed across the aneurysm's neck from outside the vessel, permanently sealing it off from blood flow.	A catheter is threaded through the wrist or groin artery up into the brain; soft platinum coils (or, for select complex aneurysms, a mesh flow-diverting stent) are placed to slow flow into the sac and let it clot off from within.
Access	Open surgery through the skull	Through the blood vessels; no skull opening
Anesthesia	General anesthesia	General anesthesia (moderate sedation for select diagnostic cases)
Typical hospital stay	2–5 days for elective, unruptured cases	1–2 days for elective, unruptured cases
Typical post-treatment recovery	4–8 weeks before full activity	1–2 weeks before full activity
Durability	Very durable once clipped; low re-treatment rate	Effective, but coiled aneurysms are followed with imaging since some re-open over time and occasionally need re-treatment

	Surgical Clipping	Endovascular (Coiling / Flow Diversion)
Aneurysm shape	Well suited to wide-necked aneurysms difficult to coil safely	Well suited to narrow-necked, favorably shaped aneurysms; flow diversion extends treatment to large or complex, previously untreatable aneurysms
Location	Often preferred for aneurysms with nearby branch vessels that need direct visualization	Often preferred for aneurysms deep in the skull base or brainstem region that are harder to reach surgically
After rupture with blood clot	Can address a large blood clot compressing the brain in the same operation	Not typically used to remove a large associated blood clot
Age / medical fitness	Requires fitness for a longer open operation	Often better tolerated in older patients or those with significant other medical conditions

	Surgical Clipping	Endovascular (Coiling / Flow Diversion)
Recovery	Longer recovery; incision and skull healing add several weeks before full activity	Shorter recovery; small groin or wrist access site
Follow-up imaging	Less frequent; a clipped aneurysm rarely needs repeat treatment	Periodic MRA, CTA, or angiogram to confirm the aneurysm stays closed off, sometimes for years
Medication after treatment	None specific to the aneurysm itself	Flow-diverting stents and some coiling cases require temporary blood-thinning medication to prevent clot formation on the device
Visible scar	A hairline scar along the incision, usually hidden within the hairline	A small puncture site, usually at the wrist or groin crease

Endovascular Techniques

Which Endovascular Technique Fits Which Aneurysm?

"Endovascular treatment" covers several distinct techniques, each suited to a different aneurysm shape and location. As a rule of thumb: intrasaccular flow disruptors such as the WEB device tend to work best for wide-necked aneurysms at a vessel bifurcation, while flow-diverting stents tend to work best for wide-necked aneurysms along the internal carotid artery, where there is no nearby branch for the stent to cross. Select a technique below for detail.

Select a technique on the left to learn more.

Your Care Journey

What Happens to Me?

Select each step below to see what happens and why.

Results

What Outcomes Can Patients Expect?

Evidence from clinical trials and long-term follow-up, presented honestly, including risks.

<1%

Average annual rupture risk for a previously unruptured aneurysm, though risk varies widely by size, shape, and location, from well under 0.5% to several percent per year.

2–3%

Reported rate of a treatment-related bleed or major complication with either clipping or coiling, according to the American Association of Neurological Surgeons.

7.4%

Absolute reduction in death or dependency at one year with coiling versus clipping for ruptured aneurysms suitable for either technique (International Subarachnoid Aneurysm Trial, Lancet, 2002/2005).

The ISAT trial's advantage for coiling applies specifically to ruptured aneurysms judged suitable for either approach; longer-term follow-up found a somewhat higher chance that a coiled aneurysm would need re-treatment compared with a clipped one, which is why coiled aneurysms are followed with periodic imaging. For unruptured aneurysms, for wide-necked or unusually shaped aneurysms, and for a good number of ruptured aneurysms as well, clipping remains the better, sometimes the only, option. This is a decision made case by case, not a blanket rule in either direction. Brown's cerebrovascular team also treats a subset of large, complex, or previously untreatable aneurysms with flow-diverting stents, an area of active clinical outcomes research within the department.

Risks and Side Effects

Every aneurysm treatment carries risk, and we discuss these in detail before any procedure. With surgical clipping: risks include stroke, bleeding, infection, seizure, and, rarely, injury to a nearby nerve or brain structure. With endovascular treatment: risks include stroke, vessel injury, groin or wrist access-site bleeding, and, with flow-diverting stents, blood clot formation on the device if blood-thinning medication is stopped early.

After a ruptured aneurysm specifically, the aneurysm itself is only the first problem. Roughly a third of patients develop vasospasm, a narrowing of the brain's arteries that peaks 4 to 14 days after the bleed and can cause a second, delayed stroke (delayed cerebral ischemia) even after the aneurysm has been successfully secured. This is why patients stay in a specialized neurocritical care unit for close monitoring during that window, not just for the procedure itself. Other possible complications after a rupture include hydrocephalus (fluid buildup requiring a temporary or permanent drain) and seizures.

Most patients with an unruptured aneurysm who undergo elective treatment do well and return to their normal activities. Outcomes after a ruptured aneurysm depend heavily on how severe the bleed was and how quickly treatment began; some patients recover fully, others are left with lasting deficits, and aneurysmal subarachnoid hemorrhage carries a real risk of death, which is why we treat any suspected rupture as a true emergency.

Frequently Asked Questions

Common Questions

I was just told I have an unruptured aneurysm. Do I need surgery right away?

Usually not. Most small, incidentally found aneurysms are monitored rather than treated immediately. Your team will look at the aneurysm's size, shape, and location, your age and health, and your family history to estimate its specific rupture risk and weigh that against the risk of treatment. Many patients are followed safely with periodic imaging for years.

How is an aneurysm actually found?

Most unruptured aneurysms are found incidentally, on an MRI or CT scan ordered for an unrelated reason such as headaches or a head injury. When an aneurysm is suspected, we confirm it with a CT angiogram (CTA) or MR angiogram (MRA), and sometimes with a catheter-based cerebral angiogram, which gives the most detailed picture of the aneurysm's shape and its relationship to nearby vessels.

Will I be awake during clipping or coiling?

No. Both surgical clipping and endovascular coiling or flow diversion are performed under general anesthesia, so you are fully asleep throughout the procedure.

Can an aneurysm come back after treatment?

A clipped aneurysm rarely reopens. A coiled aneurysm can, over time, compact and re-open a small remnant, which is why coiled aneurysms are followed with periodic imaging, typically for several years; if a remnant grows, it can usually be re-treated with additional coils or a flow-diverting stent.

Is a brain aneurysm hereditary? Should my family be screened?

Aneurysms can run in families. If you have one first-degree relative (parent, sibling, or child) who has had a brain aneurysm, your own risk is roughly four times higher than average. Screening with MRA is generally recommended if you have two or more affected first-degree relatives, or a personal or family history of certain connective-tissue or kidney conditions linked to aneurysms, such as autosomal dominant polycystic kidney disease.

What is a "sentinel headache"?

A smaller, self-limited leak from an aneurysm can occasionally cause an unusually severe headache days to weeks before a larger rupture. It's called a sentinel headache because, in hindsight, it was a warning sign. Any sudden, severe, new headache deserves urgent medical evaluation, since there is no reliable way to tell a sentinel headache from a common headache without imaging.

How long is recovery after treatment?

After elective coiling or flow diversion for an unruptured aneurysm, most patients go home within a day or two and resume normal activity within a week or so. After elective clipping, hospital stay is typically several days, with several weeks before returning to full activity. Recovery after a ruptured aneurysm is longer and more variable, often including a stay in a rehabilitation facility, and depends heavily on how severe the initial bleed was.

What should I do if I think I'm having a ruptured aneurysm?

Call 911 immediately. Do not drive yourself. A sudden, severe headache unlike any before, especially with neck stiffness, vomiting, light sensitivity, or any change in alertness, needs emergency evaluation right away. Early treatment meaningfully improves the chance of a good outcome.

Our Team

Meet the Cerebrovascular Team

Brown Neurosurgery's Cerebrovascular/Skull Base Surgery/Endovascular Neurosurgery Division treats aneurysms with both open surgical and endovascular techniques, reviewed together at a weekly multidisciplinary cerebrovascular conference.