Sickle Cell Disease: Ratio of Blood Flow Velocity of Intracranial to Extracranial Cerebral Arteries-Initial Experience

Purpose: To establish reference values of the ratios of flow velocity in the middle cerebral artery (V-MCA) and the terminal portion of the internal carotid artery (V-tICA) to flow velocity in the extracranial portion of internal carotid artery (V-ICA) in children with sickle cell disease (SCD). Materials and Methods: Institutional ethics committee approval and parental informed consent were obtained for this prospective HIPAA-compliant study. Sixty-eight children (38 female; mean age, 7.7 years +/- 3.3; range, 2-14 years) with HbSS genotype, without neurologic deficits and no history of stroke, were enrolled. Final study population comprised 56 (mean age 8.0 +/- 3.3 years, 26 females) children who underwent magnetic resonance (MR) angiography, which excluded intracranial arterial narrowing, transcranial color-coded duplex ultrasonography (US), and carotid US to determine V-MCA/V-ICA and V-tICA/V-ICA ratios from angle-corrected and uncorrected velocities. Tolerance interval estimates were used to calculate reference ranges and linear regression was used to quantify associations of Doppler parameters with age adjusted for hemoglobin and hematocrit. Results: Reference ranges in centimeters per second for mean angle-corrected V-MCA on the left and right sides were 62-198 and 69-153; those for V-tICA were 30-196 and 36-175; and those for V-ICA were 18-116 and 15-95, respectively. Reference ranges for mean angle-corrected V-MCA/V-ICA ratio on the left and right sides were 1.2-4.0 and 0.4-3.4 and those for V-tICA/V-ICA ratio were 0.5-2.9 and 0.5-2.7, respectively. V-MCA, V-tICA, and V-tICA/V-ICA ratio were not age dependent, contrary to V-ICA and V-MCA/V-ICA ratio, after controlling for hematocrit and hemoglobin. Conclusion: The study provides reference limits for V-MCA, V-tICA, V-ICA, and velocity ratios obtained from children with SCD.