A proposed ordinal scale for grading histology in elastase-induced, saccular aneurysms

The elastase-induced aneurysm model in rabbits, though widely applied, still offers no quantitative or qualitative metric for histologic outcome. This study is aimed at producing such a scale to evaluate outcome and facilitate meaningful, preclinical comparison among devices proposed for aneurysm treatment.

Elastase-induced aneurysms were created and embolized in 30 rabbits. Aneurysms were harvested between 2 and 24 weeks. Specimens were embedded in paraffin, sectioned, and stained with hematoxylin and eosin. The scale comprised 3 subcategories: extent and degree of recanalization/coil compaction; neck healing, based on thickness and type of tissue across the neck; and dome healing. Neck healing was assessed by both gross and microscopic inspections. Compaction was assessed by using both the angiographic and histologic images. Dome healing was assessed by using the microscopic images only. Data were analyzed with either analysis of variance for the quantitative data or Kruskal-Wallis tests when analyzing the nonparametric data.

We noted a significant main effect for healing over time (P = .0016). Post hoc tests showed that, at 2 weeks, the mean score was 1.4 +/- 0.8, as compared with a mean score of 7.2 +/- 1.6 for the 24-week time point (P < or = .05). Further, significant differences in healing between narrow-necked (6.0 +/- 1.3) and wide-necked aneurysms (3.5 +/- 1.1) were seen at 4 weeks (P = .0433). The dynamic range of the scale also appears to be appropriate, because there was adequate range at the upper portion of the scale to reflect improved healing that might be achieved with future devices.

This scale is a potentially relevant outcome measurement tool for elastase-induced aneurysms after endovascular therapy. Future studies are still required to confirm its practical relevance.