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

OBJECTIVE

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.