Unruptured Brain Aneurysm

An unruptured brain aneurysm is a bulge or ballooning in a blood vessel in the brain. While many aneurysms do not rupture, those that bleed can cause serious medical complications. Clinical decisions to monitor the aneurysm or intervene with surgery depend on the size, location and shape of the bulge. Treatment options typically include surgical clipping or endovascular coiling to prevent future rupture.

What Is an Unruptured Intracranial Aneurysm?

An intracranial aneurysm is a weakened, ballooned-out pouch on the wall of an artery inside your brain. Most look like small berries at branch points (saccular or berry aneurysms). An unruptured aneurysm hasn't bled. Roughly 2–3% of adults carry one without knowing it. The large majority will never rupture. When a brain aneurysm does rupture, it causes a subarachnoid hemorrhage — a type of stroke that kills about a third of patients.

At a Glance

An unruptured aneurysm is a weak, ballooned-out spot on a brain artery — most are found by accident on a scan for something else
The majority of small aneurysms never bleed; the average annual rupture risk across all comers is under 1% per year
Risk depends on size, location, age, blood pressure, smoking status, and family history — the PHASES score puts these together into a 5-year estimate
Three main treatment options: careful observation with repeat imaging, open microsurgical clipping, or endovascular repair (coiling, stent-assisted coiling, or flow diversion)
Whether to treat — and how — is a judgment call that should be made at a center that does all three approaches in high volume

Symptoms

Unruptured aneurysms usually cause no symptoms at all. Most are discovered incidentally.

When unruptured aneurysms do cause symptoms (larger or specific locations)

A new drooping eyelid with a dilated pupil on one side — classically from a posterior communicating artery aneurysm compressing the third cranial nerve (urgent attention needed)
Double vision or trouble moving one eye
Facial pain or numbness
Visual changes from an aneurysm pressing on the optic nerve

Warning signs that an aneurysm may have bled — these are 911 emergencies

The worst headache of your life, coming on in seconds ('thunderclap' headache)
Sudden stiff neck, nausea, or vomiting with a severe headache
Brief loss of consciousness or confusion

Diagnosis

CT angiography (CTA) and MR angiography (MRA)

Non-invasive; both give a 3-D picture of the arteries in your brain and can measure size, shape, and location.

Digital subtraction angiography (DSA)

Gold standard. A catheter is threaded from the wrist or groin up into the arteries of the neck and contrast dye is injected. Shows the finest anatomic detail; often the same procedure during which endovascular coiling is performed.

Key questions from the scans

How big is it? (Size is the strongest single predictor of rupture)
Where is it? (Posterior circulation is riskier)
What shape? (Irregular or multi-lobed aneurysms carry higher risk)
Is it growing? (Growth on comparison imaging is a red flag)
Are there others? (~20-30% of patients have more than one)

Types

By Shape

Saccular (berry) — most common; a balloon on the side of an artery at a branch point
Fusiform — longer, spindle-shaped; involves a whole segment of artery; needs flow diversion or bypass
Dissecting and mycotic — result from a tear in the artery wall or infection; individualized treatment

By Location

Anterior communicating artery (ACom) — most common site for ruptured aneurysms; deep midline location makes open surgery challenging
Posterior communicating artery (PCom) — a growing PCom aneurysm can cause a drooping eyelid with a dilated pupil
Middle cerebral artery (MCA) — often have branches coming off the aneurysm; traditionally better candidates for microsurgical clipping
Ophthalmic / paraclinoid ICA — near the optic nerve; increasingly treated with flow diversion
Basilar tip and other posterior circulation — carry higher rupture risk at any size; often treated endovascularly

Treatment

Observation with surveillance imaging

For small, stable aneurysms in low-risk locations — especially in older patients. Repeat MRA or CTA at 6–12 months then annually. Smoking roughly doubles rupture risk — quitting is the single most effective preventive intervention.

Microsurgical clipping

The original aneurysm operation; most durable cure. A titanium clip is placed across the aneurysm neck permanently. Preferred for MCA aneurysms, complex aneurysms with branches, and wide-necked aneurysms in younger patients. Performed with intraoperative angiography or ICG video angiography.

Endovascular coiling

Catheter-based; no craniotomy. Soft platinum coils are packed inside the sac until blood can no longer enter. Coiled aneurysms can recanalize in ~10-20% of cases — follow-up imaging required.

Stent-assisted coiling

For wide-necked aneurysms where coils would fall out. A stent is placed across the aneurysm neck first as a scaffold. Requires blood thinners (aspirin + clopidogrel) for several months.

Flow diversion (Pipeline and similar)

A braided metal mesh tube placed in the parent artery across the mouth of the aneurysm. Blood stops flowing into the sac, which gradually thromboses. Complete occlusion in ~75-85% of patients at one year. Best for large, wide-necked, or fusiform aneurysms along the internal carotid artery. Requires dual antiplatelet therapy for at least 6 months.

Outcomes

PHASES score	5-year rupture risk	What it means
0-2	~0.4%	Very low; observation usually safest
3-5	~0.7-1.3%	Low
6	~1.7%	Intermediate; treatment often considered
7-8	~2.4-3.2%	Intermediate-high; treatment usually recommended
≥10	~5-17%	Very high; treatment strongly favored

Periprocedural risk at experienced centers:

Microsurgical clipping: ~1.7% mortality, ~6-7% overall morbidity
Endovascular coiling: ~1-2% mortality, ~4-5% unfavorable outcome
Flow diversion (large/giant carotid aneurysms): ~5-6% major stroke or neurologic death; complete occlusion ~75-95% at 1-5 years

References

Thompson BG, et al. Guidelines for management of patients with unruptured intracranial aneurysms (AHA/ASA). Stroke. 2015;46(8):2368-2400. PMID: 26089327
Greving JP, et al. Development of the PHASES score for prediction of risk of rupture of intracranial aneurysms. Lancet Neurol. 2014;13(1):59-66. PMID: 24290159
UCAS Japan Investigators. The natural course of unruptured cerebral aneurysms in a Japanese cohort. NEJM. 2012;366(26):2474-2482. PMID: 22738097
Becske T, et al. Pipeline for uncoilable or failed aneurysms: results from a multicenter clinical trial. Radiology. 2013;267(3):858-868. PMID: 23418004
Molyneux AJ, et al. ISAT of neurosurgical clipping versus endovascular coiling in 2143 patients: randomised comparison. Lancet. 2005;366(9488):809-817. PMID: 16139655

Our Specialists

Issam A. Awad, MD

Neurosurgery

Omer Doron, MD, PhD

Neurosurgery

Jehad Zakaria, MD

Neurosurgery

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