In ICA stenosis with ipsilateral ECA internalization, how does the ECA appear on Doppler?

• A. ECA mimics ICA with forward diastolic flow
• B. ECA becomes occluded
• C. ECA shows high-resistance pattern with no diastolic flow
• D. ECA flow ceases

Answer: (D)

In ICA stenosis, the brain can recruit collateral pathways from the external carotid artery to perfuse intracranial vessels. When the ECA becomes a major source of intracranial flow, it is effectively internalized, and most of its flow is directed into intracranial collaterals rather than distally through the ECA branches. On Doppler, this redistribution often results in little or no detectable forward flow in the ECA itself, appearing as flow ceasing. This pattern reflects collateral circulation taking over the intracranial supply rather than a normal or occlusive pattern of the ECA.