This review evaluated adverse outcomes after surgical clipping and endovascular coil embolisation of unruptured intracranial aneurysms. The authors concluded that reporting bias may have led to an underestimate of morbidity and mortality after surgical clipping. The limited search, incomplete reporting of review methods, and differences between the studies make it difficult to assess the reliability of the results.

To evaluate rates of adverse outcomes after the treatment of unruptured intracranial aneurysm (UIA) with surgical clipping and endovascular coil embolisation, and to examine potential sources of bias.

MEDLINE was searched for studies published in English from 1990 to July 2003; the search terms were reported. The reference lists of identified studies were screened.

Study designs of evaluations included in the review

Studies that included more than 10 patients were eligible for inclusion. The duration of follow-up in the included studies ranged from immediately post-operative to 16.3 months. The studies were classified as single-centre, multicentre or community-based.

Specific interventions included in the review

Studies that evaluated surgical clipping or endovascular coil embolisation (coiling) were eligible for inclusion.

Participants included in the review

Studies of patients with UIA were eligible for inclusion. The mean age of the patients was 57 years in studies of clipping and 53 years in studies of coiling. The participants had varying sizes (from small to giant) and locations of aneurysms (details were reported).

Outcomes assessed in the review

Studies that reported treatment outcomes separately for ruptured intracranial aneurysms and UIAs were eligible for inclusion. The review assessed the adverse outcome rate (AOR), which was defined as the combined outcome of all-cause early or in-hospital morbidity and mortality. Outcomes were assessed for the time interval closest to 3 months. The included studies used a variety of definitions for the AOR (the definitions used in the individual studies were reported).

How were decisions on the relevance of primary studies made?

Two reviewers independently conducted searches; no further details were reported.

The authors did not state that they assessed validity.

Two reviewers independently extracted the data and any disagreements were resolved by a third reviewer. Where sufficient data were presented for individual studies, the review authors re-calculated the AORs using data from the modified Rankin scale, Glasgow Outcome Scale or reported patients' outcome data; for studies that did not present sufficient data, reported AORs were used. The data were re-calculated for patients with UIAs.

How were the studies combined?

The studies were grouped by type of treatment (coiling or clipping) and the range of AORs, as well as the cumulative rate (no details of methods used), was reported. The risk of publication bias was examined by plotting the AOR against the sample size separately for clipping and coiling studies.

How were differences between studies investigated?

The risk of bias was examined by plotting the AOR against the median study year separately for clipping and coiling studies. AORs for retrospective single centre studies, prospective single-centre studies and multicentre or community-based studies were calculated separately and the data were indicated separately on the scatter plots.

A total of 49 studies (n=14,651) were included. The sample size ranged from 10 to 3,498.

Nineteen studies evaluated coiling (n=1,967 in the tables; n=1,925 in the text): 7 seven prospective studies (n=852) and 12 retrospective studies (n=1,115). Ten were retrospective single-centre studies, five were prospective single-centre studies and four were multicentre or community-based.

Thirty studies evaluated clipping (n=12,684 in the tables; n=11,363 in the text): 4 prospective studies (n=2,963), 23 retrospective studies (n=7,640) and 3 community-based studies (n=2,081). Twenty-one studies were retrospective single-centre studies, one was a prospective single-centre study and eight were multicentre or community-based.

Coiling.

The AORs ranged from 0 to 30% and mortality varied from 0 to 12%. Procedural mortality ranged from 0 to 9.7%; most studies reported procedural mortality as 0%.

The cumulative AOR was 8.8% (95% confidence interval, CI: 7.6, 10.1). For single-centre retrospective studies the AOR was 8.1% (95% CI: 6.2, 10.4).

The plot of AOR versus median study year showed that AORs have declined since the introduction of coiling in the early 1990s.

Clipping.

The AORs ranged from 0 to 25.1%. The cumulative AOR was 17.8% (95% CI: 17.2, 18.6).

The plot of AOR versus median study year showed that AORs increased in the 1990s. For prospective multicentre and community-based studies the cumulative AOR was 19.7% (95% CI: 18.9, 20.5). For retrospective studies the AOR was 7.9% (95% CI: 6.7, 9.3).

Findings suggest that reporting bias may have led to an underestimate of morbidity and mortality after surgical clipping. Coiling studies were less affected.

The review question was clear in terms of the intervention and participants and was broadly defined in terms of the outcomes and study design. The search, which was restricted to articles published in English and listed in one database plus reference lists, was very limited. This raises the potential for language and publication bias and might have resulted in the omission of other relevant studies; the authors assessed the potential for publication bias and found some evidence of its presence. A more extensive search for relevant reports would have been appropriate given the review's focus on reporting bias. Methods were used to minimise reviewer errors and bias in the extraction of data but, since the study selection process was not completely described, it was unclear whether similar steps were taken when selecting the studies. Some details of the individual studies were presented but study validity was not assessed.

The methods used to calculate the overall AORs were not reported, so the appropriateness of the methods used cannot be judged. The results of statistical tests for the association between AOR and study year, sample size and study type were not reported, hence evidence supporting conclusions about the influence of these factors could not be adequately assessed. It was not clear whether the grouping of studies (according to number of centres and study design) was planned prospectively or was the result of a post hoc examination of the data. The limited search, incomplete reporting of review methods, and differences between the studies make it difficult to assess the reliability of the results.

Practice: The authors did not state any implications for practice.

Research: The authors stated that there is a need for well-designed prospective randomised controlled trials to compare surgical clipping and endovascular coil embolisation.

Weitzman Family Fellows Research Program for the Study of Malformations of the Vasculature, grant number 642212; Richard and Jenny Levine Fund.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.