Cerebral Aneurysm Size and Distal Intracranial Hemodynamics: An Assessment of Flow and Pulsatility Index Using Quantitative Magnetic Resonance Angiography.

BACKGROUND: The relationship between cerebral aneurysm size and risk of rupture is well documented, but the impact of aneurysms on distal intracranial hemodynamics is unknown. OBJECTIVE: To examine the relationship between aneurysm size and distal intracranial hemodynamics prior to treatment. METHODS: Patients seen at our institution between 2006 and 2015 with cerebral aneurysms within the internal carotid artery (ICA) segments (proximal to ICA terminus) were retrospectively reviewed. Patients were included if the aneurysm was unruptured, and were excluded if a contralateral aneurysm was present. Flows within bilateral ICAs and middle cerebral arteries (MCA) were measured prior to any treatment using quantitative magnetic resonance angiography. Pulsatility index (PI = [systolic - diastolic flow velocity]/mean flow velocity) within each vessel was then calculated. Hemodynamic parameters were analyzed with respect to aneurysm size. RESULTS: Forty-two patients were included. Mean aneurysm size was 13.5 mm (range 2-40 mm). There was a significant correlation between aneurysm size and ipsilateral MCA PI (P = .006; r = 0.441), MCAipsilateral/ICAipsilateral PI ratio (P = .003; r = 0.57), and MCAipsilateral/MCAcontralateral PI ratio (P = .008; r = 0.43). Mean PI in the ipsilateral ICA was 0.38 (range 0.17-0.77) and ipsilateral MCA was 0.31 (range 0.08-0.83), and mean PI in contralateral ICA was 0.35 (range 0.19-0.57) and MCA was 0.30 (range 0.07-0.89). CONCLUSION: Larger aneurysm size correlates with higher ipsilateral MCA PI, demonstrating that aneurysms affect distal intracranial hemodynamics.