Possible causes include the “weight of the coil mass and the biomechanical forces exerted on the coiled aneurysm,” researchers suggest.
Basilar apex aneurysms that measure 10 mm or greater may be more likely to tilt and to lead to bending of the basilar artery after endovascular coiling than smaller aneurysms, with possible ill effects, according to a new observational study.
“Over time, evolving skills and devices have made endovascular therapy the preferred method for treating most, if not all, basilar apex aneurysms,” Ansaar T. Rai, MD (West Virginia University, Morgantown, WV), and colleagues note in their paper published online recently in the Journal of NeuroInterventional Surgery. But the morphological changes that sometimes arise after coiling “may lurk under the surface, possibly unrecognized and so potentially underreported” as a complication, they say.
“Diseased arteries with underlying risk factors are more prone to this phenomenon and since arteries with aneurysms are by definition diseased, it is possible that in large aneurysms, the large basilar bend, the flow dynamics, and the addition of a coil mass induces a structural change in the aneurysm-artery relationship, which in extreme cases may cause significant morbidity,” Rai et al explain.
With better understanding, it’s possible that certain aneurysm types might stand to benefit from modification of endovascular techniques and devices, they suggest.
Cutoff Set at 10 mm
Rai and colleagues sought to better understand how changes in the shape of the basilar artery and aneurysm that happen after coiling might lead to morbidity. In a series of 94 consecutively treated patients, a prospective aneurysm database captured measurements of the basilar artery radius-of-curvature as well as the aneurysm-tilt-angle. The researchers used these numbers to compare between aneurysms that were small (maximum dimension of < 10 mm) versus large (≥ 10 mm). Mean aneurysm size was 9 mm, and mean volume was 507 mm3. At initial presentation, 46% of the aneurysms had ruptured.
Most patients (78%) underwent only one procedure though some had as many as four, and treatments were a mix of coiling alone and cases with adjunctive stent or balloon use. Aneurysm size did not vary among the different types of intervention. As would be expected, mean coil mass was greater for the larger aneurysms (1.9 vs 0.4 g), as was the mean total coil volume (187 vs 32 mm3; P < 0.001 for both).
Over a median follow-up time of 24 months, aneurysms ≥ 10 mm tilted more than their smaller counterparts (mean 13.5º vs 1.1º; P < 0.001). For the larger aneurysms, the basilar artery also grew more curved (mean 1.3 vs 0.25 mm; P = 0.002).
“There was no significant association between underlying comorbidities such as hypertension, diabetes, hypercholesterolemia, and smoking with the geometric changes,” the researchers report, adding that stent use also appeared to have no impact.
Comparing coil mass to the heft of a quarter or a few dimes, Rai and colleagues point out that the addition of this amount of mass paired with biomechanical forces “may induce a structural change in these large aneurysms.” Other factors that might interplay with aneurysm size and structural change include the approach to stent placement as well as the configuration of the posterior cerebral arteries, they suggest.
“Possible, but speculative, strategies to reduce these geometric changes may include structural support using adjunctive stents, intraluminal flow diversion, intrasaccular flow disruptive devices, or coils with lighter mass and better radiolucency,” the researchers conclude.
Rai AT, Tarabishy AR, Boo SH, et al. The 'bendy' basilar: progressive aneurysm tilting and arterial deformation can be a delayed outcome after coiling of large basilar apex aneurysms. J NeuroIntervent Surg. 2018;Epub ahead of print.
Rai et al report having no relevant conflicts of interest.