Introduction Aneurysmal rupture is a rare but serious outcome for those with intracranial aneurysms (IAs), but treatment for IAs carries its own risks. Therefore, clinicians require accurate metrics to identify IAs at higher risk of rupture, thus exposing only those patients to the risks of treatment. Murray’s Law describes the angles and radii of parent (r₀ ) and daughter vessels (r₁ , r₂ ) at an ideal bifurcation which minimize the energy cost required to transport and metabolically maintain blood. Murray’s Law (r₀ ^x = r₁ ^x + r₂ ^x ) states that ideal bifurcations will have a junctional exponent of x_ideal = 3 and predicts ideal bifurcation angles (Θ_i,ideal ) for given radii. Deviation from this geometry increases energy cost, which may lead to increased wall shear stress (WSS), predisposing to IA formation and rupture. The objective of this study was to investigate the association of deviation from Murray’s Law with bifurcation-type IA presence and rupture status.

Materials and Methods Measurements were made on 3D models acquired from radiologic imaging of patients with IAs of the basilar tip (BT), middle cerebral artery (MCA), and internal carotid artery (ICA) bifurcations. Deviations from x_ideal and ideal angles were calculated as |x_observed - x_ideal | and ∑_i|Θ_i,observed - Θ_i,ideal |, respectively. Paired t-tests were used when a contralateral comparison was available. Otherwise, unpaired t-tests were used. All t-tests used a critical value of α = 0.05.

Results Results are shown in table 1. A total of 36 patients with IAs were included. Deviation from ideal radii did not predispose to IA formation, but deviation from ideal angles at the MCA and BT bifurcations did (aneurysmal and non-aneurysmal values for ∑_i|Θ_i,observed - Θ_i,ideal | at MCA: 155°, SD = 58° versus 59.5°, SD = 29.8°, p < 0.001, n = 10; at BT: 135°, SD = 61° versus 76.5°, SD = 41.0°, p = 0.010, aneurysmal n = 10, non-aneurysmal n = 13). Deviation from ideal radii and angles did not increase risk of rupture.

Conclusion This study investigates how deviation from ideal geometry may relate to IA formation and is the first to explore its potential association with IA rupture. Deviation of angles may be more predictive of IA formation than deviation of radii, although conclusions are limited by the small sample size. Future studies will investigate the relationship between non-ideal bifurcation geometry and WSS using computational fluid dynamics to better understand how these phenomena relate to one another and to aneurysmal pathology.

Disclosures S. Street: None. P. Palmisciano: None. S. Hoz: None. G. Ventre: None. N. Agyeman: None. A. Matur: None. J. Castiglione: None. M. Johnson: None. S. Peyman: None. M. Smith: None. M. Zuccarello: None. J. Forbes: None. N. Andaluz: None. C. Prestigiacomo: None.