Background Endovascular interventions typically require placement of a device in the cerebral vasculature. Knowledge of the cerebrovascular geometry can aid in designing conformable devices. The study's objective was to establish baseline measurements of the anterior circulation in the cerebral vasculature including diameter, length and vessel taper.

Materials and Methods The sample size was determined for four cohorts based on gender and side; males-right, males-left, females-right and females-left. We reviewed similar measurements in the literature and conservatively chose a SD of 0.5 mm. Using a margin of error of 0.2 and a 95% CI yields a sample size of 25 patients for each sub-group for a total of 100 patients. The sample was calculated from a patient population that had undergone an intracranial CT angiogram. The age cut-off was set at 40 years based on our experience that most patients undergoing neurovascular interventions are above this age group. Patients with any vascular abnormality on the CTA were excluded. Thus 50 consecutive male and female patients were included. The vessel diameter was measured at the proximal cavernous ICA, the ICA terminus, the MCA origin and an M2 origin. The vessel length between these endpoints was calculated along the centerline. The vessel taper was calculated as the change in caliber per mm of length.

Results The mean length of the ICA from the proximal cavernous segment to the ICA terminus was 33.1±6.1 mm. The mean diameter at the proximal cavernous ICA and the ICA terminus was 5±0.6 mm and 3.6±0.4 mm respectively. The mean ICA taper was 0.04±0.02/mm. For the MCA, the diameter at the M1 and M2 origins measured 3.1±0.4 mm and 2.4±0.4 mm respectively. The mean MCA length was 22.5±8.1 mm. There was no significant difference between male and female patients and between right and left sides. Patients who were older than 60-years had longer ICAs (p=0.02), larger ICA-cavernous (0.003), ICA-terminus (<0.0001) and MCA origin (p=0.01) diameter than those younger than 60-years.

Conclusion We demonstrate the baseline dimensions of the anterior cerebrovascular circulation. Calculation of the vessel taper has not been done before and is important as an increasing number of endo-luminal devices are becoming available. Knowledge of the vessel taper can allow for development of more conformable devices thus enhancing their effectiveness. We are currently analyzing similar data for the posterior circulation and if accepted intend to present that along with the anterior circulation.

Competing interests A Rai: Stryker Neurovascular. B Cline: None. J Hogg: None.