Management of unruptured intracranial aneurysms (UIAs) poses a conundrum to physicians. The prevalence of UIAs is approximately 3%, the majority of which are discovered incidentally. Rupture of an aneurysm can have devastating effects with high morbidity and mortality, but the vast majority of aneurysms do not rupture. Aneurysm repair, which can be performed with either open surgical or endovascular approaches, effectively eliminates the risk of rupture, but carries a risk of procedural complications. Shared decision-making, taking into account age, general health status, personal preferences, and the patient-specific risk of rupture and procedural complications is advisable.
Modifiable risk factors for aneurysm rupture include smoking, hypertension, and alcohol abuse; these should be addressed in all patients with UIA.
If an aneurysm is causing a cranial neuropathy, a classic example being a third nerve palsy from a posterior communicating artery aneurysm, repair should be pursued as this indicates an expanding aneurysm.
Aneurysms in the cavernous carotid artery do not cause subarachnoid hemorrhage, as the blood is contained within the cavernous sinus; they should only be repaired if causing a cranial neuropathy or rarely if very large in size.
Risk of rupture increases with aneurysm size, with 7 mm often considered a threshold of increased risk warranting intervention. However, other risk factors such as anatomical configuration of the aneurysm, location, and personal or family history (two or more first-degree relatives) of prior rupture also influence risk (see box in algorithm). Patient age is important. Younger patients are exposed to greater risk of rupture given their longer life span; they are also at lower risk of procedural complication. Scores to predict the risk of rupture may assist with decision making.
For patients with smaller aneurysms (< 7 mm), decision-making is complex and there is not consensus on which patients to treat. Most of those with very small aneurysms (< 4 mm) should be observed unless multiple high-risk features are present. Neurovascular consultation is indicated when the optimal treatment strategy is in question.
Both open surgical clipping and endovascular treatment of aneurysms are effective. A meta-analysis of surgical treatment showed a 1.7% mortality rate and an overall morbidity rate of 6.7%. Patient age ≥ 50 years, aneurysm size ≥ 12 mm, and aneurysms located in the posterior circulation were predictors of poor surgical outcome. Endovascular treatment options include coiling, stent-assisted coiling, and endoluminal flow diversion. A meta-analysis showed a 4.8% total unfavorable outcome rate for endovascular treatment, but also a 9.1 % retreatment rate. Aneurysm morphology (e.g., wide neck) and size should be considered when choosing which strategy to use for repair. In general, endovascular coiling is associated with lower treatment morbidity and mortality, but clipping offers a lower recurrence rate.
Aneurysm growth is significantly associated with rupture, but the likelihood of growth is generally low, particularly for small aneurysms. A typical recommendation is to perform follow-up vascular imaging at 1 year. Magnetic resonance angiography is the preferred noninvasive imaging method, since it does not expose patients to radiation and an exogenous contrast agent is not needed. If stability is demonstrated on follow-up imaging, the ideal long-term surveillance plan is controversial, but interval imaging can be decreased or even stopped for many patients.