Extracranial-to-intracranial conversion: postoperative vascular remodeling in moyamoya disease after...

Effective revascularization in moyamoya disease (MMD) entails not only the formation of extracranial-intracranial (EC-IC) collaterals but also a postoperative shift in perfusion responsibilities-from intracranial arteries to newly established extracranial pathways. This dynamic process, characterized by extracranial collateral ingrowth (EC-Ingrowth) and regression of intracranial arterial supply (IC-Regression), represents a redistribution of cerebral perfusion we define as EC-IC conversion. However, its extent and determining factors remain poorly understood. This study aimed to quantify EC-IC conversion and identify its associated clinical and vascular factors.

We retrospectively analyzed 121 hemispheres from 92 patients with MMD who underwent combined revascularization between January 2018 and July 2022. EC-Ingrowth was graded using the Matsushima system, whereas IC-Regression was assessed according to pre- and postoperative changes in arterial supply from the internal carotid artery and vertebral artery systems. Associations between EC-Ingrowth and IC-Regression were evaluated, and factors related to these postoperative changes were analyzed.

Better EC-Ingrowth was significantly associated with female sex, younger age, left hemisphere involvement, and greater preoperative moyamoya vessel abundance (all P < 0.05). Postoperative donor-related arterial remodeling, particularly superficial temporal artery dilation and deep temporal artery participation, was also associated with more favorable EC-Ingrowth (all P < 0.05). EC-Ingrowth was positively correlated with IC-Regression (P < 0.001), and greater EC-Ingrowth was independently associated with more pronounced IC-Regression (P < 0.001).

Postoperative EC-IC conversion reflects a coordinated pattern of vascular redistribution after bypass surgery in MMD, in which greater EC-Ingrowth is closely associated with more pronounced IC-Regression. As an integrated angiographic framework, EC-IC conversion may help characterize one major manifestation of postoperative vascular remodeling and provide additional insight into the evaluation of revascularization in MMD.