Computerized assessment of angiographic occlusion rate and coil density in embolized human cerebral aneurysms

Abstract

Background and purpose: Computerized methods have been introduced for more objective quantification of angiographic occlusion rate and coil density as parameters of successful embolization. This study aimed 1) to evaluate this new computerized method for angiographic occlusion rating and coil density calculations by comparison with corresponding histometric parameters from retrieved human aneurysms, and 2) to compare the new computerized method with the present standard of subjective angiographic occlusion rating.

Materials and methods: From 14 postmortem-retrieved human aneurysms, angiographic occlusion rate was determined by contrast medium attenuation-gradient distinction on digital subtraction angiographs after Guglielmi detachable coil (GDC) embolization. Angiographic coil density was calculated, approximating aneurysms as ellipsoid and coils as cylindric volumes. On surface-stained histologic ground sections of the respective aneurysms, the occluded aneurysm area and coil area were measured. Then, we calculated and compared the histometric occlusion rates and coil densities with the corresponding angiographic parameters by using the Wilcoxon paired signed-rank test and the Spearman rank correlation.

Results: Computerized angiographic occlusion rates (75%-100%) showed good correlation (r = 0.799; P < .01) with histometric occlusion-rates (61%-100%), resulting in no statistically significant differences (P = .2163). With 5.1% (+/-3.8), the mean difference between computerized angiographic occlusion rates and histometry was substantially lower compared with 10.7% (+/-8.7) mean difference between subjective angiographic estimations and histometry. Calculated angiographic coil density (13%-32%) significantly differed from histometric coil density (8%-35%; P < .05).

Conclusions: For recanalized aneurysms, computerized angiographic occlusion rating showed better correspondence with histometry compared with subjective angiographic occlusion rating. Clinical application of this new tool may lead to more objective cutoff values for re-embolization indications. The value of coil density calculations seems limited by the approximation of the aneurysms as ellipsoid volumes.

Fig 1.

A–C, Anterior communicating artery aneurysm #1 (male patient; age, 35 years; survival, 2 days) with subjective occlusion rating of 100% and computerized occlusion rating of 96%. A, Preinterventional angiograph. Band C, Enlarged details of the postembolization DSA. C, Aneurysmal border is outlined in red, the neck plane with red arrows. The green false-color labeling of the contrast medium shows minimal inflow in the neck region. D and E, Micrographs (barr 5 mm) of 1 surface-stained ground section of aneurysm #1 through the neck region and the parent arteries. In 1E, the aneurysmal sac is outlined in red, the orifice plane with red arrows, and the total length in black. The metallic coil sections are false-color labeled in red, and the recanalized areas (D) are green labeled. In the center of the aneurysm, fresh red static thrombus, the basis for subsequent granulation tissue organization, can be seen.

Fig 2.

A–E, Basilar bifurcation aneurysm #13 (female patient; age, 43 years; survival, 36 days) with a subjective occlusion rate of 95% and a computerized occlusion rate of 89%. A, Preinterventional anteroposterior angiograph. Band C, Enlarged details of the postembolization anteroposterior DSA, the aneurysmal border in red and neck plane outlined with red arrows. C, Residual filling (green areas) in the aneurysmal neck region. D and E, Enlarged details of the postembolization lateral DSA projection, showing a larger contrast medium inflow area (green in 2E) between coil loops protruding caudally over the neck plane. F and G, Micrographs (bar 5 mm) of 1 surface-stained ground section of aneurysm #13 through the neck region and 1 parent artery (PA). F, Note the attenuated blue-stained fibrin clot (FI) and red thrombus (RT) in the center, and the subarachnoid hemorrhage (SAH). G, Aneurysmal border, orifice plane, and metallic coil sections are outlined and labeled in red. Some coil loops are protruding the orifice plane, and the inflow area, appearing pale stained without red thrombus in 2F, is labeled in green.

Fig 3.

A–E, basilar bifurcation aneurysm #14 (female patient; age, 40 years; survival, 41 days) with a subjective and computerized occlusion rate of 100%. A, Preinterventional anteroposterior angiogram. B and C, Enlarged details of the postembolization anteroposterior DSA. C, The aneurysmal border is outlined in red, the neck plane with red arrows. An embolized caudal part of the aneurysm protrudes over the neck plane. D and E, Enlarged details of postembolization lateral DSA projection. D, The protruding part of the aneurysm (B) can be located posteriorly to the basilar artery. On both DSA projections (C and E), no false-color labeled contrast medium inflow into the aneurysm can be discerned. F–I, Micrographs (bar 5 mm) of 2 surface-stained ground sections of aneurysm #14 through the neck region and the parent arteries (PA). F, Note the attenuated blue-stained fibrin clot (FI) in the aneurysmal center. In G, the aneurysmal sac, orifice plane, and metallic coil sections are outlined and labeled in red. No residual inflow area can be discerned and false color labeled in 3 hours. Enlarged detail (magnification 10 ×) from a consecutive ground section, showing a zone of fibrovascular repair (FVR) covering the orifice. I, Further enlarged detail (magnification 140 ×) of the rectangle in 3 hours, showing a new vessel wall (NVW) with endothelial lining (EL). In the organized thrombus, multinucleated foreign-body giant cells (FBGC) can be discerned at the outer and inner coil interfaces (arrows).

Fig 4.

Bland-Altmann plots comparing the differences of computerized angiographic occlusion rating (red) and subjective occlusion rating (green) with the reference parameter of the histometric occlusion rate. Especially for the clinically most relevant group of aneurysms with high recanalization, it is shown that the differences are considerably lower for computerized occlusion rating compared with subjective estimations.