• Aneurysm
• Device
• Intervention

We read with interest the article by Fiorella et al1 on interobserver variability in the assessment of aneurysm occlusion with the WEB aneurysm embolisation system recently published in the journal. In this study the authors evaluated the interobserver variability of the previously published Web Occlusion Scale (WOS).2 They showed substantial overall interobserver agreement and proposed that the WOS should be used as a primary angiographic endpoint in future clinical studies.

We have just completed a retrospective multicenter study addressing the safety of the use of single layer WEBs in 98 aneurysms.3 In this study we described a new classification, the Beaujon Occlusion Scale Score (BOSS), for follow-up evaluations. This score is applicable to both single and dual layer WEBs. However, unlike the WOS, the BOSS system takes into account situations where the WEB itself is still filled with contrast media. BOSS 1 corresponds to opacification of the WEB alone, whereas in BOSS 1+3 conditions we can also see residual opacification of the aneurysmal sac (figure 1).

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Figure 1

Beaujon Occlusion Scale Score: 0, no residual flow inside the aneurysm or the WEB; 0′, opacification of the proximal recess of the WEB; 1, residual flow inside the WEB; 2, neck remnant; 3, aneurysm remnant; 1+3, contrast agent is depicted inside and around the device.

We suggest that this is of major interest, not least because instances of WEB devices remaining filled with contrast media on follow-up evaluation are far from rare. In the single layer WEB study, short-term imaging follow-up was available in 70% of cases with an average time of 3.3 months. Upon early evaluation, BOSS 1 or BOSS 1+3 were found in 15% of cases. Furthermore, in our unpublished study, in a cohort of 26 WEB treatments with an available follow-up of more than 6 months, residual opacification was found in the device in seven cases (27%).

We also contend that it is important to differentiate aneurysm remnants (BOSS 3) from an isolated residual filling of the WEB (BOSS 1). Although in most cases BOSS 1+3 remnants should be considered for retreatment, in BOSS 1 cases the aneurysm rupture risk is probably low and complete occlusion may be observed during subsequent follow-up.

Nevertheless, in some cases, BOSS 1 grades can persist. In our institution four BOSS 1 or 1+3 cases (15%) were detected at mid-term follow-up (>12 months) in the absence of any antiplatelet regimen. In these cases, if retreatment is deemed necessary, determination of the ideal strategy could be difficult. Considering that most of the aneurysms are bifurcation aneurysms, complementary treatment with a flow-diverter stent would not be without risk.4

We therefore recommend the use of the BOSS classification system, rather than the WOS, for future studies which strive to evaluate the long-term efficiency of WEB devices.