1. Introduction Internal carotid artery occlusion (ICAO) can cause recurrent ipsilateral stroke due to hemodynamic failure of the cerebral collateral supply (1). In the case of ICAO, the primary collateral circulation based on the circle of Willis (CoW) is first activated (Supplementary Figure 1). However, if this primary compensatory route is insufficient, recruitment of secondary collaterals including leptomeningeal vessels occurs, indicating inadequate circulation through the CoW (2).
