Difference in aneurysm characteristics between ruptured and unruptured aneurysms in patients with multiple intracranial aneurysms
- Neuroradiological Clinic, Neurocenter, Klinikum Stuttgart, Germany
- Neurosurgical Clinic, Neurocenter, Klinikum Stuttgart, Germany
- Neurological Clinic, Neurocenter, Klinikum Stuttgart, Germany
- Medical Faculty, University Duisburg-Essen, Germany
Neuroradiological Clinic, Neurocenter, Klinikum Stuttgart, Germany
DOI:10.4103/sni.sni_339_17Copyright: © 2018 Surgical Neurology International This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: P. Bhogal, M. AlMatter, V. Hellstern, O. Ganslandt, H. Bäzner, H. Henkes, M. Aguilar Pérez. Difference in aneurysm characteristics between ruptured and unruptured aneurysms in patients with multiple intracranial aneurysms. 10-Jan-2018;9:1
How to cite this URL: P. Bhogal, M. AlMatter, V. Hellstern, O. Ganslandt, H. Bäzner, H. Henkes, M. Aguilar Pérez. Difference in aneurysm characteristics between ruptured and unruptured aneurysms in patients with multiple intracranial aneurysms. 10-Jan-2018;9:1. Available from: http://surgicalneurologyint.com/surgicalint-articles/difference-in-aneurysm-characteristics-between-ruptured-and-unruptured-aneurysms-in-patients-with-multiple-intracranial-aneurysms/
Background:The risk of aneurysmal rupture is dependent upon numerous factors, however, there are inconsistencies in the results between studies, which may be due to confounding factors. This can be avoided by comparing the characteristics of ruptured and unruptured aneurysms within the same patient. We sought to analyze the aneurysm characteristics of patients with acute aneurysmal subarachnoid hemorrhage (SAH) and multiple intracranial aneurysms.
Methods:We reviewed our prospectively maintained institutional database, between 01/10/2007 and 01/01/2017, for all patients with confirmed SAH and >1 aneurysm. We recorded the size, location, and morphology and calculated secondary geometric indices such as bottleneck factor and aspect ratio.
Results:During the study period, a total of 694 patients with aneurysmal SAH were admitted to our institution. We identified 113 patients (74.3% female, average age 51.7 ± 12.3). The majority of patients had only one associate unruptured aneurysm (79.6%). The average unruptured aneurysm was 3.1 ± 1.5 mm and the average ruptured aneurysm was 5.7 ± 2.7 mm (P P 7 mm (OR, 17.74; 95% CI 4.07–77.35; P
Conclusion:Size plays an important part in determining rupture risk, however, other factors such as location and in particular morphology must also be considered. We believe that the introduction of vessel wall imaging will help to risk stratify aneurysms.
Keywords: Aneurysm morphology, aneurysm, aspect ratio, bottleneck factor, lobulation, subarachnoid hemorrhage
Approximately 2–3% of the population harbours an unruptured intracranial aneurysm, and approximately 30% of the patients have multiple aneurysms.[
Identifying which aneurysms, regardless of size, are prone to rupture is the key to optimizing management. A variety of different factors such as aneurysm shape, size ratio, and flow angles[
An inability to control for confounding factors may cause much of the difficulty when using a case-control design when analyzing patients with ruptured aneurysms to those with unruptured aneurysms. This can be avoided by comparing the characteristics of ruptured and unruptured aneurysms within the same patient.
We sought to analyze the morphological characteristics of ruptured and unruptured aneurysms within the same patient from a single institution.
We reviewed our prospectively maintained institutional database, which includes consecutive patients with confirmed SAH. We extracted all patients who presented with acute aneurysmal SAH confirmed by computed tomography (CT) or magnetic resonance imaging (MRI). We included all patients between 01/10/2007 and 01/01/2017 with confirmed SAH and more than one intracranial aneurysm confirmed on diagnostic subtraction cerebral angiography (DSA). We excluded patients without confirmed aneurysmal SAH (missing CT/MRI or DSA), patients presenting with fusiform, dissecting, mycotic, and partially thrombosed aneurysms, as well as likely pseudoaneurysms secondary to trauma.
All patients underwent either CT or MRI to confirm the presence of SAH and CT or MR angiography to confirm the presence of an aneurysm. All patients presenting with SAH underwent DSA with complete 6-vessel angiography. In addition to the standard Towne's and lateral projections, dedicated projections of all aneurysms were performed as per our standard practice.
Aneurysmal location, measurements, and morphological characteristics
The location of the ruptured and unruptured aneurysms was categorized into internal carotid artery (ICA), anterior cerebral artery territory (ACA), anterior communicating artery (AcomA), posterior communicating artery (PcomA), middle cerebral artery (MCA), vertebral artery (VA), posterior inferior cerebellar artery (PICA), basilar artery (BA), and the posterior cerebral artery (PCA).
The maximum neck width, dome width, and dome height were recorded from the DSA using standard techniques. We calculated secondary geometric indices including the aspect ratio (AR) – the ratio of the dome height to the neck width, the height to width ratio, and the bottleneck factor – the ratio of dome width to neck width.[
Aneurysm shape was categorized as spherical (if the width was at ≥80% of the dome height), lobulated (where the lobules were smooth and of approximately the same size), or complex/irregular (when the lobules were asymmetric or multiple lobules were seen).
Statistical analysis was performed using Stata/IC 14.2 for Windows (StataCorp LP, 4905 Lakeway Drive, College Station, TX 77845, USA). Numeric variables were presented in the form of mean ± SD (min − max) and categorical variables as frequencies. Correlative analyses were performed using the Mann–Whitney U test, Fisher's exact test, or the Chi-square test. P values less than 0.05 were considered statistically significant.
During the study period, a total of 694 patients with aneurysmal SAH were admitted to our institution. We identified 113 patients who met our inclusion and exclusion criteria. The majority of the patients were female (n = 84, 74.3%). The average age of the patients was 51.7 ± 12.3 years (range 21.8–85.6 years).
The majority of the patients had only one associate unruptured aneurysm (79.6%), but up to 5 associated unruptured aneurysms were recorded. The total number of associated unruptured aneurysms was 148. The number of associated aneurysms is shown in
Aneurysmal size, location, and morphology
The average size of the unruptured aneurysms was 3.1 ± 1.5 mm (range 1.0–9.5 mm), and the average size of the ruptured aneurysms was 5.7 ± 2.7 mm (range 1.8–19.0 mm). There was a significant difference in the size of ruptured and unruptured aneurysms (P < 0.001). The unruptured aneurysms were overwhelmingly <7 mm (n = 146, 98.6%), with the majority being <5 mm (n = 131, 88.5%). Similarly, the majority of the ruptured aneurysms were also <7 mm (n = 91, 80.5%) and close to half were smaller than 5 mm (n = 52, 46.0%). The AR was significantly larger in ruptured aneurysms (1.8 ± 0.7, range 0.6–3.8 vs. 1.5 ± 0.5 range 0.4–2.9, P < 0.001) between the two cohorts. Similarly, the bottleneck factor was also significantly larger in ruptured aneurysms (1.7 ± 0.6, range 0.7–3.8 vs. 1.3 ± 0.4, range 0.1–3.0, P < 0.001).
The majority of the aneurysms were located in the anterior circulation (n = 227, 86.9%) with the majority of the ruptured aneurysms located in the anterior circulation (n = 94, 83.9%). The most frequent location for both the unruptured and ruptured aneurysms was the MCA (n = 54, 36.0% and n = 33, 29.5%, respectively), with the ICA representing the second most frequent location of unruptured aneurysms and the AcomA representing the second most frequent location for ruptured aneurysms.
The majority of the unruptured aneurysms were smooth and had a regular morphology (n = 113, 76.4%) compared to only 15.9% of ruptured aneurysms. Conversely, a significant majority of ruptured aneurysms were irregular (n = 87, 77.0%) with a minority of unruptured aneurysms having an irregular morphology (n = 20, 13.5%). The aneurysm characteristics are shown in
In the multivariate analysis and after matching for age and sex, aneurysm location, aneurysm morphology, and size were independently associated with rupture. A complex aneurysm morphology was the strongest risk factor for rupture (OR, 29.27; 95% CI, 14.33–59.78; P < 0.001) with size >7 mm (OR, 17.74; 95% CI, 4.07–77.35; P < 0.001) and AcomA location also showing a strong independent association. Interestingly, although a lobulated appearance showed an increased risk, this did not reach statistical significance (OR, 3.45; 95% CI, 1.27–9.37; P < 0-001 0.015), suggesting that an increasingly irregular morphology is important in the risk of rupture. The characteristics of the two cohorts after matching for age and sex are shown in
A variety of factors have been implicated in the rupture of aneurysms. Aneurysmal dome size is naturally one of the most widely recognized risk factors, and at the moment size still remains the most widely used geometrical factor when determining the decision to treat. Aneurysms over 10 mm carry a 1.9% per year risk of rupture; however, size alone cannot be used as the only measure upon which to base treatment decisions, and recent studies have shown that size alone is not a good predictor.[
The size ratio, introduced by Dhar et al.,[
Irregular shape is another important variable linked to rupture. A Japanese observational study demonstrated that unruptured aneurysms with daughter sacs have a higher rupture rate than aneurysms with regular shapes,[
Applying the results of post-rupture morphological analysis to determine the risk of rupture relies on the premise that post-rupture morphology is not significantly altered from the pre-rupture state.[
Routine imaging with MRI or CT angiography is the accepted standard of care for patients with small aneurysms with treatment considered if there are signs of growth. There is an increasing awareness that imaging of the wall may help to delineate which aneurysms are at risk of growth and rupture prior to any actual morphological change. One technique that shows early promise is contrast-enhanced black blood vessel wall MRI. Several cases and case series have been published that have shown a high accuracy in determining which aneurysm has ruptured in cases of multiple aneurysms.[
Our study is limited by the inherent weaknesses of a retrospective study design and the fact that visual confirmation of the ruptured aneurysm was not obtained in all aneurysms. A further limitation is that the measured variables such as irregularity and size may be a result of aneurysm rupture rather than a cause. We believe that future prospective studies should include aneurysm wall imaging preferably with black blood contrast-enhanced MRI. These studies may help to highlight the potential to detect inflammation and wall changes prior to rupture in aneurysms irrespective of size, location, etc., and help to risk stratify patients appropriately.
Aneurysm size is important in determining the risk of rupture; however, the morphology of aneurysms is also extremely important, and as others have reported the shape of an aneurysm may be more important in determining its rupture risk. We believe that rather than relying on size alone we must consider a larger number of features when determining the treatment strategy for our patients. As has been shown the pre and post-rupture appearance cannot be assumed to be the same, and a pre-rupture evaluation of the aneurysm wall is essential in accurately risk stratifying patients.
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Conflicts of interest
There are no conflicts of interest.
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