Immediate Anatomic Results after the Endovascular Treatment of Unruptured Intracranial Aneurysms: Analysis of the ATENA Series

Discussion

The ATENA study showed that endovascular treatment of unruptured intracranial aneurysms is feasible in a high percentage of patients with low morbidity and mortality rates.¹ However, a crucial issue for endovascular techniques is the uncertainty of whether coils provide long-term durability of aneurysm occlusion and protection from aneurysm rupture.³

The question of the efficacy of endovascular treatment of unruptured aneurysms is fundamental but until now was not analyzed in a large series of patients with a precise methodology. The efficacy can be evaluated from both anatomic and clinical points of view. We know from the literature regarding the endovascular treatment of ruptured aneurysms that there is a clear relationship between the quality of aneurysm occlusion and the risk of rebleeding. In the CARAT (Cerebral Aneurysm Rerupture After Treatment) study conducted in a cohort of 1010 patients treated for ruptured aneurysms with coil embolization or surgical clipping, the risk for rerupture was strongly associated with the degree of aneurysmal occlusion (cumulative risk: 1.1% for complete occlusion, 2.9% for 91%–99% occlusion, 5.9% for 70%–90% occlusion, and 17.6% for < 70% occlusion).⁴ Despite some methodologic limitations of CARAT (anatomic results abstracted from procedural reports leading to the heterogeneous evaluation method singularly in the clipping group and absence of independent core laboratory analysis), it seems that the protection afforded against rebleeding is related to the quality of the aneurysmal occlusion. Is the risk for rupture of unruptured aneurysms treated by the endovascular approach similarly associated with the quality of the aneurysmal occlusion? To answer this question, it is first necessary to know the precise quality of the aneurysmal occlusion immediately after the treatment and to analyze which factors affect the immediate anatomic results. These points are evaluated in the present analysis. On the contrary, the relationship between the quality of occlusion and the risk of bleeding is not analyzed in our study because long-term follow-up is not available at the present time.

In assessments of the immediate postoperative anatomic results from a large series of patients with endovascular treatment of intracranial aneurysms, 2 major points must be recognized:

1. Several scales can be used to evaluate anatomic results after endovascular treatment of ruptured or unruptured aneurysms. The 3-grade Montreal scale is the most frequently used.² In this scale, grade I is complete closure of the aneurysm, including the neck. A residual neck (grade II) is defined as the persistence of any portion of the original defect of the arterial wall observed on any single projection but without opacification of the aneurysmal sac. Any opacification of the sac is classified as a residual aneurysm (grade III). Consistent with observations by Raymond et al,² we found that sometimes a precise analysis of the immediate postoperative anatomic results was difficult when a minimal opacification was visible inside the coil mesh. Under those conditions, it is relatively difficult to assign classifications according to the scale, and some heterogeneity may be introduced from one series to another (see below).

2. To overcome this limitation, the analysis of anatomic results by an independent core laboratory is certainly useful but is rarely performed for the assessment of the anatomic results of endovascular treatment of ruptured and/or unruptured aneurysms.^3–9 Reports on recent series have shown that the evaluation conducted by the treating physician is often different from the evaluation performed by an independent core laboratory; the analysis by the treating physician tended toward better anatomic results.¹⁰ In the ATENA study, the anatomic results were evaluated rigorously by an independent core laboratory that included 2 experienced neuroradiologists (L.P. and L.S.) who had performed endovascular treatments for more than 10 years.

In contrast to observations in other series, the evaluations of the postoperative anatomic results by the treating practitioner or by the core laboratory were not significantly different globally.¹⁰ However, some large inconsistencies were observed with a low agreement between the treating physician and core laboratory (κ = 0.33). For example, the treating neuroradiologist judged the results from 426 aneurysms as complete occlusions, but the core laboratory judged the same group of results as 335 complete occlusions (78.6%), 61 neck remnants (14.3%), and 30 aneurysm remnants (7.0%). On the other hand, the treating neuroradiologist judged the results from110 aneurysms as aneurysm remnants, and the core laboratory judged the same group of results as 46 aneurysm remnants (41.8%), 34 neck remnants (30.9%), and 30 total occlusions (27.3%). These discrepancies are related to the difficulties in determining the rate of occlusion after endovascular treatment. As outlined before, 1 major limitation of the Montreal scale is the uncertainty regarding the classification of aneurysms in which the neck occlusion is complete, but some contrast filling is present in the coil mesh. These patterns are classified as grade A by some practitioners (as suggested by Raymond et al²) and grade C by others.

According to the core laboratory, the postoperative anatomic results in the ATENA series showed that a satisfactory occlusion (complete occlusion or neck remnant) was obtained in 593 aneurysms (85.4%). It is difficult to compare our series with previous reports on large series because of the methodologic heterogeneities outlined above. In the Wanke series,⁶ complete or nearly complete occlusion was achieved in 34 (89.5%) of 38 aneurysms. In the Gonzalez series⁸ of 233 aneurysms, angiographic results revealed complete occlusion in 138 (59.2%), neck remnants in 92 (39.5%), and incomplete occlusion in 3 (1.3%), with a high rate of satisfactory occlusion (98.7%). In the Terada series,⁷ the results showed complete occlusion in 33 (45.2%) of 73 aneurysms, neck remnants in 26 (35.6%) of 73 aneurysms, and aneurysm remnants in 14 (19.2%) of 73 aneurysms, with a satisfactory occlusion in 80.8%. In the Gallas series,¹¹ postoperative occlusion was classified as complete in 207 aneurysms (70.0%), subtotal in 84 aneurysms (26.1%), and incomplete in 11 aneurysms (3.9%), with a satisfactory occlusion in 96.1%. In the Standhardt series complete occlusion was achieved in 57.5%, neck remnants in 34.0%, and aneurysm remnants in 8.5%, with satisfactory occlusions in 91.5%.⁹ Thus, the high rate of satisfactory occlusion (between 80.8% and 98.7%) confirmed the immediate anatomic efficacy of endovascular treatment.

We found improved anatomic results in patients younger than 65 years compared with older patients (Table 1). Several factors may explain this difference including increased difficulties in the endovascular treatment and different strategy of treatment in elderly patients. As the cumulative risk for rupture is lower in older patients, the objective of having a very dense coil mesh is probably considered less important in elderly patients. The clinical analysis has shown that the morbidity rate is significantly higher in patients older than 65 years, and it can explain, in some cases, the premature interruption of treatment. The degree of postoperative aneurysm occlusion was not significantly related to aneurysm location (Table 2). This suggests that the endovascular treatment is equally effective for aneurysms in all locations. We found that 2 anatomic factors were linked to the quality of aneurysm occlusion: aneurysmal size and the dome-to-neck ratio (Tables 3 and 4). The quality of occlusion was better in aneurysms smaller than 6 mm than those larger than 6 mm in diameter. Similar results were previously reported by Terada et al,⁷ Gonzalez et al,⁸ and Standhardt et al.⁹ The anatomic results were also better in narrow-neck aneurysms (dome-to-neck ratio > 1.5) compared with wide-neck aneurysms (dome-to-neck ratio < 1.5). This was also previously demonstrated by Gonzalez et al⁸ and Standhardt et al.⁹ Our evaluation of the techniques used showed that anatomic results were similar when coiling and remodeling were used but worse with stent placement (Table 5). However, the recruitment of patients in the ATENA study took place when stents were just beginning to come into use; thus, further analyses in a larger group of patients treated with stents are certainly needed to define more clearly the efficacy of stent placement.

There were several limitations to our study. First, the immediate postoperative anatomic results only represented 1 part of the anatomic efficacy of endovascular treatment. The other part of this efficacy is the prevention of the recanalization; this will be analyzed with mid- and long-term follow-ups. A second limitation was that it was not possible to analyze the relationship between the quality of postoperative anatomic results and the clinical efficacy of the endovascular treatment to prevent aneurysmal rupture because long-term clinical follow-up is actually not available. A third limitation, outlined above, was the difficulty in analyzing anatomic results with the Montreal scale. However, the definitions used in other scales are probably equally difficult; this emphasizes the importance of evaluating a large series of patients in determining whether recanalization can be more precisely predicted.