What is the treatment for an unruptured aneurysm?

Treatment of Unruptured Intracranial Aneurysms

For unruptured intracranial aneurysms, treatment decisions depend primarily on size, symptoms, and patient age—with symptomatic aneurysms requiring treatment, asymptomatic aneurysms <5mm managed conservatively with surveillance imaging, aneurysms ≥10mm warranting strong consideration for intervention, and the 5-10mm range requiring individualized risk-benefit analysis based on location, morphology, and patient factors. 1

Symptomatic Aneurysms

All symptomatic unruptured aneurysms should be treated with rare exceptions, regardless of size. 2, 1 Symptoms indicating mass effect or potential impending rupture include:

• Cranial neuropathies (particularly sudden third nerve palsy suggesting expansion and imminent rupture) 1
• Persistent headaches 1
• Visual deficits 1
• Seizures 1
• Ischemic symptoms from intrasaccular thrombus 2

Treatment should proceed with relative urgency for acutely symptomatic aneurysms. 2

Size-Based Treatment Algorithm

Small Aneurysms (<5mm)

Conservative management with surveillance imaging is recommended for virtually all asymptomatic incidental aneurysms <5mm. 1 The rupture risk is extremely low at 0.05% per year for anterior circulation aneurysms <7mm without prior subarachnoid hemorrhage history. 1

• Periodic follow-up with MRA or CT angiography should be performed to detect growth 2, 1
• Initial surveillance at 6-month intervals is warranted for newly diagnosed aneurysms, as 5.2% of patients show growth at 6 months 3
• Annual surveillance may be appropriate after initial stability is documented 1

Medium Aneurysms (5-10mm)

Aneurysms >5mm in patients <60 years should be seriously considered for treatment. 1 The rupture risk is approximately 1% per year for 7-10mm aneurysms. 1

Treatment decisions must weigh:

• Patient age (younger patients benefit more from definitive treatment) 2, 1
• Aneurysm location (posterior circulation carries higher rupture risk) 2, 4
• Morphology (multilobarity and dome-to-neck ratio >1 increase rupture risk) 4
• Prior SAH history (coexisting aneurysms carry higher rupture risk) 2
• Family history of aneurysmal SAH 2, 1

Large Aneurysms (≥10mm)

Aneurysms ≥10mm warrant strong consideration for treatment in nearly all patients <70 years. 2, 1 These carry substantially higher rupture rates and should be treated unless prohibitive comorbidities exist. 2

Age-Based Considerations

Younger Patients (<60 years)

Lower threshold for treatment of aneurysms >5mm due to long life expectancy and cumulative rupture risk over decades. 2, 1 The benefit of definitive treatment increases with longer projected lifespan. 2

Older Patients (>65 years)

Observation is a reasonable alternative for small asymptomatic aneurysms given that treatment-related morbidity increases with age. 2, 1 Endovascular treatment in patients >50 years appears safer than surgical clipping, though differences may not reach statistical significance. 2

For patients >70 years with small asymptomatic aneurysms and significant comorbidities, treatment risks outweigh rupture risk—do not treat. 1

High-Risk Features Mandating Treatment Consideration

Regardless of size, the following features increase rupture risk and favor treatment:

• Prior SAH from a different aneurysm: Coexisting aneurysms carry substantially higher rupture risk 2, 1
• Posterior circulation location (particularly basilar apex): Relatively high rupture risk 2, 1, 4
• Documented growth on serial imaging: Growth indicates instability with 24-fold increased rupture risk (5% per patient-year vs 0.2% without growth) 2, 1, 5
• Family history of aneurysmal SAH: Positive family history warrants special consideration 2, 1
• Multilobarity or daughter sac formation: Associated with increased growth and rupture risk 2, 4

Treatment Modality Selection

Endovascular Coiling vs. Surgical Clipping

Both endovascular and microsurgical treatment options should be discussed with patients to ensure informed decision-making. 2, 1

Endovascular coiling may be reasonable over surgical clipping for select aneurysms, particularly at the basilar apex, in elderly patients (>60 years), or when surgical morbidity is high. 2, 1 Coil embolization offers:

• Lower procedural morbidity and mortality (7.1% vs 10.1% at 1 year for patients without prior SAH) 2
• Shorter length of stay 2
• Lower hospital costs 2
• Procedural complications in 4.8% of cases 2

However, microsurgical clipping provides more durable protection against aneurysm regrowth. 2, 1 Endovascular treatment shows:

• Aneurysm regrowth or recurrence in 24.4% over 0.4-3.2 years 2
• Retreatment required in 9.1% of cases 2

Middle cerebral artery aneurysms generally favor microsurgical clipping, while basilar apex and vertebrobasilar confluence aneurysms favor endovascular repair. 2

Critical Implementation Requirements

Treatment must be performed at high-volume tertiary centers (>20 cases annually) with experienced cerebrovascular teams, as results are inferior at low-volume centers. 2, 1 This is a Class I recommendation with Level of Evidence B. 2

Collaboration between microneurosurgeons and endovascular neurosurgeons is essential, using a decision-making paradigm designed to offer only low-risk treatments. 1

Post-Treatment Surveillance

Imaging after intervention to document aneurysm obliteration is mandatory, given the differential risk of growth and hemorrhage for completely versus incompletely obliterated aneurysms. 2, 1

• Early post-treatment imaging (typically DSA) to confirm complete obliteration 2
• Long-term follow-up imaging with CTA or MRA to detect recurrence and de novo aneurysm formation 2
• More frequent follow-up for incompletely obliterated aneurysms 2, 1
• Assessment of cognitive outcome in addition to standard measures 2, 6

Conservative Management Protocol

For aneurysms managed without intervention:

Periodic surveillance imaging is necessary to detect changes in size or configuration. 2, 1 Surveillance intervals should be:

• Every 6 months for the first year for newly diagnosed aneurysms 3
• Annually thereafter if stable 1
• More frequent (semiannual) for aneurysms ≥5mm 3

Any documented growth mandates immediate reconsideration for treatment. 2, 1 Growth occurs in 12% of aneurysms during surveillance, with annual growth rate of 3.7% per aneurysm-year. 3 Initial aneurysm size predicts growth (1.6% for <5mm vs 8.7% for ≥5mm). 3

Risk Factor Modification

Smoking cessation should be strongly counseled, as smoking increases risk of aneurysm formation and is a modifiable risk factor for growth of small aneurysms. 2, 4

Hypertension should be monitored and treated, as it may play a role in growth and rupture. 2

Common Pitfalls to Avoid

• Do not treat small (<5mm) asymptomatic aneurysms in elderly patients (>70 years) with significant comorbidities—treatment risks outweigh rupture risk 1
• Do not rely solely on non-invasive imaging for treatment planning—catheter angiography (DSA) remains the gold standard for definitive characterization 2, 1
• Do not assume all incidentally discovered aneurysms require treatment—the vast majority of small unruptured aneurysms will never rupture (only 1 in 200-400 annually) 1
• Do not use stents or flow diverters for small aneurysms amenable to primary coiling or clipping—these carry higher complication risks 6
• Do not ignore aneurysms in patients without prior SAH as "less aggressive"—incidental aneurysms show 15% growth rate vs 5% in patients with prior SAH 5