Factors influencing successful angiographic occlusion of aneurysms treated by coil embolization

Abstract

Background and purpose: Coil embolization of berry aneurysms is a relatively new treatment whose long-term efficacy has yet to be established. The purpose of this study was, first, to attempt to identify factors that might be important in predicting success both at the time of treatment and at the time of follow-up angiography, and, second, to study changes in the aneurysm between treatment and follow-up to determine the frequency of these changes.

Methods: The pretreatment, posttreatment, and follow-up angiograms of the first 63 aneurysms (in 58 patients) treated at our institution between June 1992 and April 1995 were analyzed, and the percentage of occlusion of each aneurysm was calculated. The size of any rest was noted for the posttreatment and follow-up angiograms. Treatment success was defined as a residue of less than 2 mm. Aneurysms were said to have changed if the percentage of occlusion had altered by more than 2.5% or if the difference in rest size was greater than 0.25 mm. Possible factors influencing primary and follow-up success rates were correlated against these calculations.

Results: Success rates at treatment and follow-up were 71% and 65%, respectively. No change occurred in 41% of aneurysms, and 20% had a decrease in size of the residue. Twenty-eight percent had coil compaction, and 11% had aneurysmal growth. Neck size was the only significant variable in primary treatment success. Success at follow-up correlated significantly with neck size, initial treatment success, vasospasm at the time of treatment, and clinical presentation.

Conclusion: Best long-term angiographic results are obtained when the primary treatment is successful, when the aneurysm is small and narrow-necked, when the acutely ruptured aneurysm is treated within 15 days of ictus, and with anterior communicating and basilar-tip aneurysms.

fig 1.

Aneurysmal growth. A, Pretreatment angiogram of a large, wide-necked, basilar sidewall aneurysm occurring as a mass lesion. This image is traced onto calibrated paper, with the margins of the aneurysmal lumen delineated in D as the solid black line. From the tracing, and using the linear reference value “D,” luminal size “A,” luminal width “B,” and neck size “C” are calculated (as shown in D). B, Posttreatment angiogram after coil placement. This image was used to trace the margin of the coil ball in D and to calculate the percentage of occlusion (94%) and rest size (“E ” in D). C, Follow-up angiogram at 10 months shows aneurysmal growth. After tracing this image, the new aneurysmal lumen is delineated by the outer gray line in D. The compacted coil-ball mass is now delineated by the oblique lines. D, Traced superimposed representations of A–C (artist's rendition). For clarity, only the 1-cm grid lines are portrayed (a portion of the figure shows the 1-mm calibrations as a reference). The shaded area at the aneurysmal neck represents the residual uncoiled aneurysm. The area filled with oblique lines represents the compacted coil-ball mass. “D” is the linear reference value for the calculation of “A” (maximum luminal size, 20 mm), “B” (maximum luminal width, 12.7 mm), “C” (neck size, 4.8 mm), and “E” (rest size after treatment, 5.2 mm).

fig 2.

Coil compaction. A, Pretreatment angiogram. B, Posttreatment angiogram. C, Follow-up angiogram at 7 months of a wide-necked (4.6 mm) carotid termination aneurysm. D, Traced image (artist's rendition) derived from A, B, and C. The shaded area represents the residual uncoiled lumen at the time of treatment. The area filled by oblique lines is the additional lumen exposed by coil compaction. This is an example of initial treatment success (rest size < 2 mm) converting to failure at follow-up (rest size = 3.4 mm). For clarity, only the 1-cm calibrations have been rendered, with a portion of the figure showing the full 1-mm grid lines. “D” = linear reference diameter; “A” = luminal size (12.2 mm); “B” = luminal width (8.6 mm); “C” = neck size (4–6 mm); “E” = rest size at follow-up (3.4 mm).

fig 3.

Illustration showing the sometimes poor correlation between percentage of occlusion and rest size (length of exposed aneurysmal wall after coiling). Aneurysms 1 through 4 are identical tracings. Aneurysm 1 has 100% occlusion and no rest. Aneurysms 2 through 4 all have 95% occlusion, but quite different rest sizes. The largest rest is in aneurysm 3 and the smallest in aneurysm 2. Aneurysm 5 is a magnified image of aneurysm 4, with the same percentage of occlusion but a larger rest size