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OBJECTIVES:
In patients with Internal Carotid Artery (ICA) occlusion, extracranial collateral circulation to the ICA is mainly achieved via retrograde flow in the ophthalmic artery originating from External Carotid Artery (ECA) branches. In some patients with ipsilateral ICA occlusion, the ECA will assume a low-resistance flow pattern as the brain becomes a component of the artery’s outflow bed. This phenomenon is known as internalization of the ECA. Due to lack of literature defining the frequency of this phenomenon this study was designed to calculate its prevalence and analyze flow pattern variations within the extracranial carotid arterial system.
METHODS:
This is a retrospective analysis of 100 consecutive patients with ipsilateral ICA occlusions diagnosed at a single institution from 2011 to 2014 with the use of colored duplex ultrasound (DUS). Peak Systolic and End Diastolic velocities as well as flow pattern (low resistance vs high resistance) were recorded and analyzed. Patients with Common Carotid Artery (CCA) occlusion on either side and those with bilateral ICA occlusion were not included in the current analysis. Repeated studies and patients with other pathology that can affect the ECA waveform were excluded.
RESULTS:
There were 66 male and 34 female patients with a mean age of 70.36 years. The most common occluded site was the proximal ICA. The prevalence of ECA internalization in patients with ipsilateral ICA occlusion was 28%. There was statistical significance between the mean ages in the 2 groups. ECA internalization was more common in younger patients comparing to the non “internalized” group 64.19 ± 14.16 vs 72.22 ± 11.37 years respectively (p=0.008). Mean End Diastolic Velocity (EDV) was higher in the internalization group (36.29 ± 36.76 vs 14.25 ± 15.76 p<0.0001) while there was no significant difference in gender and Peak Systolic Velocity (PSV) in the groups. Vertebral artery occlusion was identified in 3 patients. Contralateral CCA, ICA, and ECA were patent in all individuals.
CONCLUSIONS:
The prevalence of ECA internalization was only 28% in this cohort occurring more common in younger individuals. The exact reasons and clinical significance have not been studied but the size and number of ECA to ICA connections play a role.