Giant intracranial aneurysms: natural history and 1-year case fatality after endovascular or surgical treatment

J Neurosurg 134:49–57, 2021

Clinical evidence on giant intracranial aneurysms (GIAs), intracranial aneurysms with a diameter of at least 25 mm, is limited. The authors aimed to investigate the natural history, case fatality, and treatment outcomes of ruptured and unruptured GIAs.

METHODS In this international observational registry study, patients with a ruptured or unruptured GIA received conservative management (CM), surgical management (SM), or endovascular management (EM). The authors investigated rupture rates and case fatality.

RESULTS The retrospective cohort comprised 219 patients with GIAs (21.9% ruptured GIAs and 78.1% unruptured GIAs) whose index hospitalization occurred between January 2006 and November 2016. The index hospitalization in the prospective cohort (362 patients with GIAs [17.1% ruptured and 82.9% unruptured]) occurred between December 2008 and February 2017. In the retrospective cohort, the risk ratio for death at a mean follow-up of 4.8 years (SD 2.2 years) after CM, compared with EM and SM, was 1.63 (95% CI 1.23–2.16) in ruptured GIAs and 3.96 (95% CI 2.57–6.11) in unruptured GIAs. In the prospective cohort, the 1-year case fatality in ruptured GIAs/unruptured GIAs was 100%/22.0% during CM, 36.0%/3.0% after SM, and 39.0%/12.0% after EM. Corresponding 1-year rupture rates in unruptured GIAs were 25.0% during CM, 1.2% after SM, and 2.5% after EM. In unruptured GIAs, the HR for death within the 1st year in patients with posterior circulation GIAs was 6.7 (95% CI 1.5–30.4, p < 0.01), with patients with a GIA at the supraclinoid internal carotid artery as reference. Different sizes of unruptured GIAs were not associated with 1-year case fatality.

CONCLUSIONS Rupture rates for unruptured GIAs were high, and the natural history and treatment outcomes for ruptured GIAs were poor. Patients undergoing SM or EM showed lower case fatality and rupture rates than those undergoing CM. This difference in outcome may in part be influenced by patients in the CM group having been found poor candidates for SM or EM.

Clinical trial registration no.: NCT02066493 (

Comparative Morphological Analysis of the Geometry of Ruptured and Unruptured Aneurysms

Neurosurgery 69:349–356, 2011 DOI: 10.1227/NEU.0b013e31821661c3

The risk of aneurysm rupture appears to be related to multiple factors such as topology, morphology, size, perianeurysmal environment, and blood flow hemodynamics.

OBJECTIVE: To evaluate aneurysm morphology and to quantitatively compare the volumetric parameters between ruptured and unruptured aneurysms from our clinical database at the UCLA Medical Center.

METHODS: Novel algorithms that automatically compute aneurysm geometry were tested on the basis of voxel data obtained from angiographic images, and measurements of aneurysm morphology were automatically recorded. We studied a total of 50 aneurysms (25 ruptured and 25 unruptured) with sizes ranging from 3 to 26 mm. To compare the geometric characteristics between ruptured and unruptured groups, we examined measurements, including volume and surface area, and the ratios of these measurements to the minimal bounding sphere around each aneurysm.

RESULTS: More than 65% of ruptured aneurysms had a ratio of aneurysm volume to bounding sphere volume (AVSV) of > 0.5. More than 70% of ruptured aneurysms had a ratio of aneurysm surface to bounding sphere surface (AASA) of < 1. A trend differentiating ruptured and unruptured aneurysms was observed in AVSV (P = .07) and AASA (P = .04). Classification and regression trees analysis showed 68% correct classification with rupture for AVSV and 70% for AASA.

CONCLUSION: By comparing aneurysm geometry with the bounding sphere, we found a trend associating the ratios of aneurysm volume and surface area with rupture. These geometric parameters may be useful for understanding the influence of morphology on the risk of aneurysm rupture.

Relationship of Growth to Aneurysm Rupture in Asymptomatic Aneurysms ≤ 7 mm: A Systematic Analysis of the Literature

Neurosurgery 68:1164–1171, 2011 DOI: 10.1227/NEU.0b013e31820edbd3

The apparent paradox of natural history data suggesting low rupture risk of small asymptomatic aneurysms and the median size of aneurysm rupture remains unexplained. Aneurysm growth rates and their potential relationship with rupture risk have not been well examined in natural history studies.

OBJECTIVE: To examine the question of whether small asymptomatic aneurysms ≤ 7 mm that are followed up over time rupture and to determine the relationship between aneurysm growth and rupture.

METHODS: We reviewed all publications on unruptured aneurysms published from 1966 to 2009. We then selected all aneurysms ≤ 7 mm for which measurements were reported for at least 2 time points and for which initial asymptomatic status and ultimate outcome (rupture vs unruptured) were reported. Using the Mann-Whitney U test, we compared absolute diameter annual growth rate.

RESULTS: Our search retrieved 64 aneurysms. Thirty aneurysms ruptured during followup, of which 27 were enlarged before rupture (90%). Thirty-four aneurysms did not rupture, of which 24 enlarged during follow-up (71%). There was a statistically significant trend toward larger absolute diameter growth for ruptured aneurysms vs unruptured aneurysms (3.89 ± 2.34 vs 1.79 ± 1.02 mm; P < .001), respectively. Annual growth rates for aneurysms for the 2 groups, however, were not statistically different (27.46 ± 18.76 vs 32.00 ± 29.30; P = .92).

CONCLUSION: Small aneurysms are prone to growth and rupture. Aneurysm rupture is more likely to occur in aneurysms with larger absolute diameter growth, but rupture can also occur in the absence of growth. The annual growth rate in both groups suggests that rate of growth of aneurysms is highly variable and unpredictable, justifying treatment or close diagnostic follow-up.

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