Endovascular Treatment of Anterior Communicating Artery Aneurysms: A Systematic Review and Meta-Analysis

DISCUSSION

In this meta-analysis, we combined data from 14 studies to analyze the representative outcomes for angiographic occlusion, procedure-related complications, and morbidity as well as mortality associated with endovascular treatment of AcomA aneurysms. Our results demonstrated that AcomA aneurysms can be successfully treated with endovascular embolization and maintain a high rate of complete or near-complete occlusion at follow-up. However, complications associated with coil embolization of AcomA aneurysms are not negligible, with a permanent morbidity rate of 6% and mortality rate of 3%.

Since the introduction of Guglielmi Detachable Coils in 1991, endovascular technique has dramatically changed the management of these aneurysms and established coiling as an acceptable alternative option to traditional clip ligation.^13,18,28,29 Large, randomized trials such as the International Subarachnoid Aneurysm Trial (ISAT) and the Barrow Ruptured Aneurysm Trial have shown that patients with ruptured aneurysms have significant advantages in disability independent survival and functional outcome when compared with those treated surgically.^30,31 However, one of the major limitations of endovascular treatment continues to be the risk of postprocedure re-bleeding. Data from ISAT and the Cerebral Aneurysm Rerupture After Treatment (CARAT) studies show significantly higher risks of re-bleeding after endovascular treatment as compared with surgical therapy.^4,32 In our meta-analysis, we found that the rate of periprocedural re-bleeding for AcomA aneurysms with endovascular retreatment was 2%, which is consistent with rates reported in CARAT and ISAT. However, recurrence or rupture of aneurysms after the initial treatment requiring retreatment by secondary coiling or clipping occurred in 7% of cases.

With the advances made in endovascular technology in recent years, the characteristics of complicated AcomA aneurysms that previously precluded treatment by coiling are increasingly challenged. The inherent small diameter of the AcomA from which the aneurysm rises as well as the propensity for AcomA aneurysms to be small in size or wide-neck are the features that can make endovascular treatment difficult.^11,13,17 Since the mid-1990s, advances in technology such as 3D rotational angiography and newer microguidewire/catheters, in combination with adjunctive devices such as balloon-assisted or stent-assisted coiling, have revolutionized treatment of aneurysms once deemed unfeasible to coil. Newer studies are beginning to examine the effects of these adjunctive devices on long-term angiographic stability and complications and recurrence rates associated with endovascular treatment; however, this is not yet well characterized for coiling therapy in AcomA aneurysms.^10,20,23

To determine any effect of advancements in technology and operator experience on the safety and efficacy of AcomA embolization, we looked at the angiographic and complication outcomes of patients in studies published before 2007 as compared with those published between 2007 and 2012. No statistically significant differences were found in our analysis of angiographic results or complications, which might be caused by underpowering. However, there was a trend suggesting decreased overall procedure-related permanent morbidity and mortality in the studies published from 2007–2012. This trend of decreased morbidity and mortality observed in patients with AcomA aneurysm over time is consistent with the finding that morbidity and mortality rates have increasingly been reduced across time among a sample of patients treated with endovascular coiling in the United States (Nationwide Inpatient Sample).^28,33,34 These studies showed that morbidity rates decreased from 7.6–4.9% in the analysis of patients treated with endovascular therapy in 1996–2000 compared with 2001–2008. Mortality rates of overall patients treated with endovascular coiling decreased from 1.7% in 1996–2000 to 0.6% in 2001–2008.

Across this time period stratification, our meta-analysis also showed that the overall aneurysm retreatment rate doubled from 5–10% when comparing studies published before and after 2007; however, the trend toward an increase was not statistically significant. Given the consistently smaller number of studies included in the “before 2007” time period stratification group, along with nationally increased use of embolization therapy over time, this increased trend found in retreatment rate may reflect a larger and more representative sample size in the 2007–2012 stratification group. Alternatively, this trend may be a result of endovascular coil embolization applied to a subset of aneurysms that are not necessarily considered “ideal” for endovascular treatment due to higher risks of recanalization.

There are several limitations to this study. Because of the highly selected cases available for analysis, this systematic review does not provide information on the proportion of all AcomA aneurysms that met the criteria for endovascular treatment. Many published studies collected data retrospectively; therefore, stratification of outcomes by rupture status and other variables such as previous rupture and number or types of adjunctive devices used was not provided in every study. The studies that were performed prospectively were not randomized studies and did not include control groups. Many of the studies included in this meta-analysis ranged in sample size, and several of the studies did not provide complete follow-up data in terms of clinical outcome or angiographic results. The included studies covered consecutive patients over many years; however, the different time periods covered largely limited our ability to stratify and scrutinize outcomes over time. Further temporal stratification of outcomes may reveal variations in complication rates over time as a result of increased experience or improvements in technology.

An important limitation of this meta-analysis is the variability inherent in assessment of angiographic outcomes for endovascular treatment of aneurysms. Multiple studies have shown only “fair” interobserver and intra-observer agreement on interpretation of the completeness of occlusion after coiling, with improvement to “moderate” agreement with follow-up angiography.^35,36 However, judgment and adjudicating aneurysms into a residual aneurysms category remain poor and can vary among observers to range from 20–60%.³⁶ The interobserver and intra-observer variability is inherent to the assessment scales used for extent of occlusion and can result in decreased variability in scales with fewer response options, though this can be less ideal for assessing effects of occlusion completeness on important outcomes such as recurrence or re-hemorrhage.^35,37 Although we were unable to individually validate the extent of occlusion for each aneurysm, many studies used the Raymond-Roy classification system³⁸ for categorization of angiographic outcomes, and we adhered to this scale as best we could, given the descriptors used in the methods for included studies. Despite this, caution is warranted when interpreting the results of this meta-analysis. It is important to consider the effects of the interobserver and intra-observer variability because the data used are gathered from case series from different institutions with the use of various technologies and equipment and conducted by specialists with ranging levels of experience and techniques.