Unruptured intracranial aneurysm (UIA)

see also International Study of Unruptured Intracranial Aneurysms.

Epidemiology

Around 3% of the adult global population has unruptured intracranial aneurysms (UIAs) ¹⁾

It is clear that more incidental intracranial aneurysms will be encountered in the future and advancing technology can be expected to demonstrate them with increasing regularity.

The prevalence of Unruptured intracranial aneurysm (UIAs) in first-degree relatives of patients with aSAH in the Hong Kong Chinese population was lower than that in Caucasians. At the same time, most of the UIAs detected in a study were small (85.7% were < 5 mm, vs 66% in a meta-analysis). With a similar incidence of aSAH in Hong Kong (7.5 per 100,000 person-years) as compared with data cited in the literature, the hypothesis that UIA rupture risk size threshold is different in Chinese patients should be further investigated ²⁾.

Natural history

Although the diagnosis of unruptured intracranial aneurysm (IA) has become more frequent, its natural history and management still remain controversial ³⁾.

A better comprehension of its evolution could optimize our therapeutic strategies.

It has been shown that even small aneurysms may enlarge and bleed unpredictably with the passage of time.

Many factors are involved in management of patients with unruptured intracranial aneurysms. Site, size, and group specific risks of the natural history should be compared with site, size, and age-specific risks of repair for each patient ⁴⁾.

Pooled multivariable analyses of individual data are needed to identify independent risk factors and to provide more reliable risk estimates for individual patients ⁵⁾.

Studies on natural history of unruptured intracranial aneurysms suggest 10 year cumulative bleeding-related mortality and severe morbidity of no less than 7.5%. In the study of Krisht et al., surgical clipping resulted in an 0.8% rate of mortality and 3.4% permanent morbidity. This suggests that surgical clipping has the potential of a superior outcome to the natural history of patients who have an estimated life expectancy of no less than 10 years ⁶⁾.

Prevalence

Higher in patients with autosomal dominant polycystic kidney disease (ADPKD) or a positive family history of intracranial aneurysm or subarachnoid haemorrhage than in people without comorbidity.

In Finland and Japan, the higher incidence of subarachnoid haemorrhage is not explained by a higher prevalence of UIAs, implicating higher risks of rupture ⁷⁾.

During 1995 to 2004, a period of increasing neuroimaging utilization, Gabriel et al., did not observe an increased rate of detection of unruptured brain arteriovenous malformation (BAVM), despite increased detection of unruptured intracranial aneurysm (IA)s ⁸⁾.

Etiology

A analysis identified differentially expressed genes and miRNAs in unruptured human cerebral aneurysms, suggesting the possibility of a role for miRNAs in aneurysm formation ⁹⁾

Rupture risk

see Unruptured intracranial aneurysm rupture risk

Screening

see Unruptured intracranial aneurysm screening.

Clinical features

Most unruptured intracranial aneurysms don’t have symptoms. “Most of these patients are found incidentally, when they get an MRI scan or computed tomography angiography scan for something unrelated.

Diagnosis

see Unruptured intracranial aneurysm diagnosis.

Treatment

see Unruptured intracranial aneurysm treatment.

Outcome

There is notable interhospital heterogeneity in outcomes among even the largest volume unruptured intracranial aneurysm referral centers. Although further regionalization may be needed, mandatory participation in prospective, adjudicated registries will be necessary to reliably identify factors associated with superior outcomes ¹⁰⁾.

Both UIA treatment modalities decided by one hybrid neurosurgeon showed low complication rates and good clinical outcomes. These results may serve as a point of reference for clinical decision-making for patients with UIA ¹¹⁾.

In a cohort of Medicare patients, there was no difference in mortality and the readmission rate between clipping and coiling of unruptured cerebral aneurysms. Clipping was associated with a higher rate of discharge to a rehabilitation facility and a longer length of stay ¹²⁾.

Surgery for incidental aneurysms of the anterior circulation can be accomplished without mortality and with an operative morbidity of 6.5%. Higher morbidity occurs in surgery for aneurysms in more difficult locations as well as larger aneurysms. The increased risk of bleeding from larger aneurysms, however, may justify the increased morbidity of surgery for these lesions. Surgery for incidental aneurysms can be recommended in healthy individuals whose anesthetic risk is acceptable and for aneurysms less than 1.5 cm in diameter arising from the middle cerebral and posterior communicating arteries. Advancing age alone is not a contraindication for surgery, nor is size greater than 1.5 cm in diameter; however, the latter factor increases the operative risk. Operations to clip aneurysms of the carotid bifurcation, carotid-ophthalmic, and anterior communicating arteries may also be recommended, but these aneurysms are more difficult to approach and surgery carries a higher morbidity. Larger aneurysms, greater than 1.5 cm in diameter, in patients over 60 years of age, and in less accessible locations may not benefit from operation because surgical morbidity for these lesions is high and with advancing age the lifetime risk of rupture has decreased. For incidental aneurysms of the posterior circulation there are insufficient data to make a recommendation regarding surgery, although it is anticipated that the counsel for anterior circulation aneurysms will apply. If operative mortality and morbidity are to be maintained at acceptable levels, incidental aneurysm surgery should be the province of the accomplished aneurysm surgeon who has available to him the most modern techniques and equipment. With the clipping of incidental aneurysms, hopefully the number of patients suffering from subarachnoid hemorrhage with its high morbidity and mortality rates can be further reduced ¹³⁾.

Cost-effectiveness

Patients' life expectancy, risk of rupture, and utility of awareness of an untreated aneurysm mainly define cost-effectiveness. However, important uncertainties remain on the rupture risk according to size and location of the aneurysm and on the utility of awareness of untreated aneurysm. More data on these factors are needed to define and individualize cost-effectiveness analyses ¹⁴⁾.

The PHASES score is an easily applicable aid for prediction of the risk of rupture of incidental intracranial aneurysms ¹⁵⁾.

The results of a study demonstrate the importance of taking the preinterventional psychiatric history into considerations when evaluating the outcome after unruptured aneurysm treatment. The unfavorable outcome of the aneurysm group seems to be caused by factors that are not related the aneurysm diagnosis or treatment itself ¹⁶⁾.

Case series

see Unruptured intracranial aneurysm case series.

Case reports

Unruptured intracranial aneurysm case reports.