Treatments for unruptured intracranial aneurysms


Intracranial aneurysms are abnormal swellings of blood vessels in the brain. They can be present without causing any symptoms, but a small proportion will eventually cause bleeding, which can cause death or serious disability. Treatment approaches for intracranial aneurysms include conservative management (treat risk factors such as blood pressure), microsurgical clipping (an operation where a clip is placed across the aneurysm), and endovascular coiling (a minor operation where a coil is placed inside the aneurysm to cause it to block). Each approach carries different potential risks and benefits, and at present there is uncertainty about the ideal approach.

Review question

We looked at the effectiveness of performing conservative treatment compared with interventional treatments (microsurgical clipping or endovascular coiling) and microsurgical clipping compared with endovascular coiling for individuals with unruptured intracranial aneurysms.

Date of search

The search is current up to 25 May 2020.

Study characteristics

We included two trials in the review: one randomized trial (a type of study in which participants are assigned to one of two or more treatments groups using a random method) published in 2011 with 80 participants, which assessed conservative treatment with endovascular coiling, and another randomized trial published in 2017 with 136 participants, which assessed microsurgical clipping compared with endovascular coiling for individuals with unruptured intracranial aneurysms.

Key results

The limited evidence available did not show differences in illness at one year for conservative treatment or interventional treatment (endovascular coiling or microsurgical clipping) of unruptured intracranial aneurysms.

Quality of the evidence

We found little evidence on the best treatment for unruptured intracranial aneurysms. The overall quality of the evidence was very low due to the small number of participants as well as to missing outcome data. Further studies with a larger number of participants are needed.

Authors' conclusions: 

There is currently insufficient good-quality evidence to support either conservative treatment or interventional treatments (microsurgical clipping or endovascular coiling) for individuals with unruptured intracranial aneurysms. Further randomized trials are required to establish if surgery is a better option than conservative management, and if so, which surgical approach is preferred for which patients. Future studies should include consideration of important characteristics such as participant age, gender, aneurysm size, aneurysm location (anterior circulation and posterior circulation), grade of ischemia (major stroke), and duration of hospitalizations.

Read the full abstract...

Unruptured intracranial aneurysms are relatively common lesions in the general population, with a prevalence of 3.2%, and are being diagnosed with greater frequency as non-invasive techniques for imaging of intracranial vessels have become increasingly available and used. If not treated, an intracranial aneurysm can be catastrophic. Morbidity and mortality in aneurysmal subarachnoid hemorrhage are substantial: in people with subarachnoid hemorrhage, 12% die immediately, more than 30% die within one month, 25% to 50% die within six months, and 30% of survivors remain dependent. However, most intracranial aneurysms do not bleed, and the best treatment approach is still a matter of debate.


To assess the risks and benefits of interventions for people with unruptured intracranial aneurysms.

Search strategy: 

We searched CENTRAL (Cochrane Library 2020, Issue 5), MEDLINE Ovid, Embase Ovid, and Latin American and Caribbean Health Science Information database (LILACS). We also searched and the WHO International Clinical Trials Registry Platform from inception to 25 May 2020. There were no language restrictions. We contacted experts in the field to identify further studies and unpublished trials.

Selection criteria: 

Unconfounded, truly randomized trials comparing conservative treatment versus interventional treatments (microsurgical clipping or endovascular coiling) and microsurgical clipping versus endovascular coiling for individuals with unruptured intracranial aneurysms.

Data collection and analysis: 

Two review authors independently selected trials for inclusion according to the above criteria, assessed trial quality and risk of bias, performed data extraction, and applied the GRADE approach to the evidence. We used an intention-to-treat analysis strategy.

Main results: 

We included two trials in the review: one prospective randomized trial involving 80 participants that compared conservative treatment to endovascular coiling, and one randomized controlled trial involving 136 participants that compared microsurgical clipping to endovascular coiling for unruptured intracranial aneurysms.

There was no difference in outcome events between conservative treatment and endovascular coiling groups.

New perioperative neurological deficits were more common in participants treated surgically (16/65, 24.6%; 15.8% to 36.3%) versus 7/69 (10.1%; 5.0% to 19.5%); odds ratio (OR) 2.87 (95% confidence interval (CI) 1.02 to 8.93; P = 0.038). Hospitalization for more than five days was more common in surgical participants (30/65, 46.2%; 34.6% to 58.1%) versus 6/69 (8.7%; 4.0% to 17.7%); OR 8.85 (95% CI 3.22 to 28.59; P < 0.001). Clinical follow-up to one year showed 1/48 clipped versus 1/58 coiled participants had died, and 1/48 clipped versus 1/58 coiled participants had become disabled (modified Rankin Scale > 2). All the evidence is of very low quality.