Review Article Imaging Evaluation for the Size of Saccular Intracranial Aneurysm

BACKGROUND

In addition to evaluate the morphologic characteristics of intracranial aneurysms, the dimension of the aneurysm is an important parameter for selecting treatment strategies, determining follow-up period, and predicting the risk of rupture. High-resolution vessel wall imaging has an increasingly dominant role in measuring aneurysm size and assessing the risk of rupture accurately. The size of saccular intracranial aneurysm may play an important role as a predictor of the rupture risk. With the rapid improvement in radiological techniques, different noninvasive imaging methods have respective characteristics in saccular intracranial aneurysms (sIA) measurement and morphologic description. Although most studies believe that the larger the aneurysm, the higher the risk of rupture, there is still a synergistic effect of multiple factors (such as location, morphology, history of aneurysmal subarachnoid hemorrhage, and even patient factors) to explain the rupture of small aneurysms.

METHODS

A literature search was performed of intracranial aneurysm size and risk of rupture.

RESULTS

The specificity and sensitivity of different imaging methods for evaluating intracranial aneurysms varied based on sizes. Rupture risk of aneurysms was associated with multiple factors. A comprehensive assessment that considered aneurysm size in conjunction with other relevant factors would be helpful in guiding options of management.

CONCLUSIONS

Accurate measurement of the dimension of sIA is an important basis in the selection of appropriate treatment including intravascular intervention or surgical clipping, as well as for determining the follow-up cycles for conservative or postoperative treatment. A uniform definition of sIA size is recommended to facilitate the integration of similar studies and to accomplish rapid and effective screening of cases in sIA treatment.

CLINICAL CHARACTERISTICS AND MORPHOLOGICAL PARAMETERS ASSOCIATED WITH RUPTURE OF ANTERIOR COMMUNICATING ARTERY ANEURYSMS

We analyzed aneurysm morphology, demographic and clinical characteristics in patients with anterior communicating artery (ACoA) aneurysms to investigate the risk factors contributing to aneurysm rupture. A total of 219 patients with ACoA aneurysms were admitted to our hospital between January 2016 and December 2020, and morphological and clinical characteristics were analyzed retrospectively in 153 patients (112 ruptured and 41 unruptured). Medical records were reviewed to obtain demographic and clinical data on age, gender, presence of hemorrhage, history of hypertension, diabetes, heart disease, and kidney disease. Morphological parameters examined on 3-dimensional digital subtraction angiography included aneurysm size, neck diameter, aspect ratio, size ratio, bottleneck ratio, height/width ratio, aneurysm angle, (in)flow angle, branching angle, number of aneurysms per patient, shape of the aneurysm, aneurysm wall morphology, variation of the A1 segment, and direction of the aneurysm. Male gender, aspect ratio, height/width ratio, non-spherical and irregular shape were associated with higher odds of rupture, whilst controlled hypertension was associated with lower odds of rupture, when tested using univariate logistic regression model. In multivariate model, controlled hypertension, presence of multiple aneurysms, and larger neck diameter reduced the odds of rupture, while irregular wall morphology increased the risk of rupture. Regulated hypertension represented a significant protective factor from ACoA aneurysm rupture. We found that ACoA aneurysms in male patients and those with greater aspect ratios and height/width ratios, larger aneurysm angles, presence of daughter sacs and irregular and non-spherical shapes were at a higher risk of rupture.

Definitions of intracranial aneurysm size and morphology: A call for standardization

Background

Intracranial aneurysms (IAs) are classified based on size (maximal dome diameter) as well as additional parameters such as neck diameter and dome-to-neck ratio (DNR). The neurosurgical literature includes a wide variety of definitions for both IA size and neck classifications. Standardizing the definitions of IA size and wide-neck classifications would help eliminate inconsistencies and potential misunderstandings of aneurysm morphology and rupture risk.

Methods

We queried the MEDLINE (EBSCO) database using the terms "unruptured IA" and ("small" or "medium" or "large") and filtered based on publication date, language, and scholarly journals. The resulting articles and their references were further screened for eligibility. This identified 286 records, of which 104 were excluded, leaving 182 articles for analysis. The review found several different IA size classifications and neck classifications.

Results

A review of the existing literature describing size and neck classifications revealed 13 size classifications for small aneurysms, four classifications for medium aneurysms, 15 classifications for large aneurysms, and one classification for giant aneurysms. There were also seven different wide-neck classifications found.

Conclusion

It is imperative that a standardization in classification be implemented to help interventionalists make the most informed decisions regarding emerging treatment options as new endovascular technologies and devices are emerging with indications based around these classifications. Based on the database findings, this article recommends standardized quantitative measurement ranges for IA size and neck classifications.

Morphological risk model assessing anterior communicating artery aneurysm rupture: Development and validation

OBJECTIVE

Prediction of the rupture risk in anterior communicating artery (ACoA) aneurysms remains challenging. We aimed to investigate the association of detailed morphologies with ACoA aneurysm rupture.

PATIENT AND METHODS

759 consecutive patients with ACoA aneurysms were identified from December 2007 to January 2016. An independent cohort was collected for validation from March 2017 to October 2019. Morphological parameters of the aneurysms were measured using CT angiography. Univariable and multivariable analyses were used to investigate the association of morphological characteristics with aneurysm rupture. Area under receiver operating characteristic curves (AUC) were used to assess the performance of the model.

RESULTS

A total of 650 patients with 650 ACoA aneurysms were included for the derivation, and 41 patients with 41 ACoA aneurysms were included for the validation. Aneurysm size, neck size, aspect ratio, size ratio, vessel angle, anterior projection, dominant A1 segment, irregular shape, the presence of a daughter dome, vessel size, and aneurysm angle were risk factors for rupture. The multivariable analysis showed that a larger aneurysm, anterior projection of aneurysms, dominant A1 segment, and irregular aneurysms were associated with aneurysm rupture, whereas larger vessel size was inversely associated with rupture. The morphological risk score showed good discrimination of ruptured and unruptured aneurysms with an AUC of 0.73 in the derivation and an AUC of 0.80 in the validation, and good calibration in both cohorts, signifying a good fit.

CONCLUSION

The morphological risk model may contribute to evaluating the risk of rupture of ACoA aneurysms.

Effect of aneurysm morphologic parameters on occlusion rates following pipeline embolization

OBJECTIVE

Treatment failures with the use of Pipeline Embolization Device (PED) continue to be observed in up to 18% of patients in large case series. Adjunctive coiling and layering of multiple devices have been shown to improve occlusion rates; however, the optimal treatment strategy with the use of PED has not been established. The purpose of this study is to identify morphological characteristics predictive of treatment failure after PED.

PATIENT AND METHODS

A case control design was used to evaluate the association of aneurysm morphologic parameters with failure after PED placement. Retrospective analysis of patients undergoing PED for elective aneurysm treatment between 2014 and 2017 was performed. Patients who underwent PED placement with at least 12 months follow-up using conventional cerebral angiography were included for further review.

RESULTS

84 patients met inclusion criteria for further analysis. ten patients (11.9%) experienced treatment failure defined by retained flow within the aneurysm and of those eight patients (9.5%) required additional retreatment. On multivariate analysis decreasing aspect ratio and increasing neck width were significant parameters that predicted treatment failure.

CONCLUSION

Aneurysms with small aspect ratio and large neck width may be more likely to experience treatment failure after PED embolization. This subset of aneurysms may therefore benefit from adjunctive coiling to improve occlusion rates. Future prospective studies are needed to validate these findings.

A retrospective comparison of sac and lobe morphology between ruptured and unruptured intracranial aneurysms

There are few reliable morphologic indices to aid in the determination of an intracranial aneurysm's rupture risk. We sought to characterize morphological characteristics of aneurysm sacs and their lobes that are associated with ruptured status at time of initial evaluation with diagnostic angiography. These factors could be associated with an aneurysm's risk of rupturing. We retrospectively reviewed all aneurysms imaged with digital subtraction angiography (DSA) at a single institution over five years. Patients presenting with aneurysmal subarachnoid hemorrhage (aSAH) were assigned to the ruptured group, and those presenting without aSAH were assigned to the unruptured group. Angiograms were evaluated for the presence of various morphological parameters. Binary logistic regression was used to assess their associations between groups. A total of 331 aneurysms among 241 patients were included in the analysis. Posterior circulation, larger size ratio, and the presence of two or more lobes were associated with aneurysm rupture (p < 0.001 for each). Aneurysms containing a lobe with a greater height than width were observed more frequently in the ruptured group (OR 5.26, 95% CI 2.66-10.41). In the receiver operating characteristic (ROC) curves, mean diameter had an AUC of 0.72 and an optimum threshold of 2.85 mm. For size ratio, the AUC was 0.70 and the optimum threshold was 2.02. A larger SR was observed in ruptured aneurysms. The presence of multiple lobes and greater lobe height than width were associated with rupture status as well. These factors merit investigation in a prospective study.

Decision-making and neurosurgeons' agreement in the management of aneurysmal subarachnoid haemorrhage based on computed tomography angiography

BACKGROUND

To determine the neurosurgeon's agreement in aneurysmal subarachnoid haemorrhage (aSAH) management with special emphasis on the rater's level of experience. A secondary aim was to analyse potential aneurysm variables associated with the therapeutic recommendation.

METHOD

Basic clinical information and admission computed tomography angiography (CTA) images of 30 consecutive aSAH patients were provided. Twelve neurosurgeons independently evaluated aneurysm characteristics and gave recommendations regarding the emergency management and aneurysm occlusion therapy. Inter-rater variability and predictors of treatment recommendation were evaluated.

RESULTS

There was an overall moderate agreement in treatment decision [κ = 0.43; 95% confidence interval ((CI), 0.387-0.474] with moderate agreement for surgical (κ = 0.43; 95% CI, 0.386-0.479) and endovascular treatment recommendation (κ = 0.45; 95% CI, 0.398-0.49). Agreement on detailed treatment recommendations including clip, coil, bypass, stent, flow diverter and ventriculostomy was low to moderate. Inter-rater agreement did not significantly differ between residents and consultants. Middle cerebral artery (MCA) aneurysm location was a positive predictor of surgical treatment [odds ratio (OR), 49.57; 95% CI, 10.416-235.865; p < 0.001], while patients aged >65 years (OR, 0.12; 95% CI, 0.03-0.0434; p = 0.001), fusiform aneurysm type (OR, 0.18; 95% CI, 0.044-0.747; p = 0.018) and intracerebral haematoma (ICA) aneurysm location (OR, 0.24; 95% CI, 0.088-0.643; p = 0.005) were associated with a recommendation for endovascular treatment.

CONCLUSIONS

Agreement on aSAH management varies considerably across neurosurgeons, while therapeutic decision-making is challenging on an individual patient level. However, patients aged >65 years, fusiform aneurysm shape and ICA location were associated with endovascular treatment recommendation, while MCA aneurysm location remains a surgical domain in the opinion of neurosurgeons without formal endovascular training.

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 < 0.001). In the multivariate analysis, 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.

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.

Interrater Agreement in the Radiologic Characterization of Ruptured Intracranial Aneurysms Based on Computed Tomography Angiography

OBJECTIVE

To determine interrater agreement in the initial radiologic characterization of ruptured intracranial aneurysms based on computed tomography angiography (CTA) with special emphasis on the rater's level of experience.

METHODS

One junior and one senior rater of 5 high-volume neurovascular tertiary centers evaluated anonymized CTA images of 30 consecutive patients with aneurysmal subarachnoid hemorrhage. Each rater described location, side, size, and morphology in a standardized manner. Interrater variability was analyzed using intraclass correlation and Fleiss' kappa analysis.

RESULTS

There was a high level of agreement for location (κ = 0.76, 95% confidence interval [CI] 0.74-0.79), side (κ = 0.95, CI 0.91-0.99), maximum diameter (intraclass correlation coefficient [ICC] 0.81, CI 0.70-0.90), and dome (ICC 0.78, CI 0.66-0.88) of intracranial aneurysms. In contrast, a lower level of agreement was observed for aneurysms' neck diameter (ICC 0.39, CI 0.28-0.58), the presence of multiple aneurysms (κ = 0.35, CI 0.30-0.40), and aneurysm morphology (blister κ = 0.11, CI -0.05 to 0.07; fusiform κ = 0.54, CI 0.48-0.60; multilobular, κ = 0.39 CI 0.33-0.45). The interrater agreement in the senior rater group was greater than in the junior rater group.

CONCLUSIONS

Interrater agreement confirms the benefit of CTA as initial diagnostic imaging in ruptured intracranial aneurysms but not for aneurysm morphology and presence of multiple aneurysms. A trend towards greater interrater agreement between more experienced raters was noticed.