Semi-Quantitative Assessment of Regional Cerebral Blood Flow Changes Following Extracranial–Intracranial Bypass Using SPECT: A Single-Center Retrospective Study

Background/Objectives: Extracranial–intracranial (EC-IC) bypass, particularly superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis, is used to augment cerebral perfusion in selected patients with moyamoya disease or atherosclerotic steno-occlusive disease. This study evaluated the impact of STA-MCA bypass on regional cerebral perfusion using a semi-quantitative SPECT area-based method. Methods: Of 40 patients screened between June 2018 and June 2022, 15 with complete paired pre- and postoperative CTA and SPECT data were included. Postoperative imaging was performed at a median of 12 months (range, 6–15 months). Proportional perfusion area in the basal ganglia and temporal regions was calculated using Labelme annotation, Canny edge detection, and Green’s theorem, normalized to total brain area. Paired comparisons and exploratory subgroup analyses were performed. Normality was assessed by Shapiro–Wilk test; Wilcoxon signed-rank tests served as sensitivity analyses. Results: Mean age was 56 ± 15.7 years (40% female). All 16 anastomoses were patent. Postoperative perfusion area increased significantly in the basal ganglia (mean difference 0.24, 95% CI 0.13–0.35, p = 0.0003) and temporal regions (0.34, 95% CI 0.08–0.60, p = 0.012). Wilcoxon tests confirmed these findings (basal ganglia p = 0.0003; temporal p = 0.008). In unilateral cases, ipsilateral and contralateral basal ganglia improvements did not differ significantly (p = 0.839). Results should be interpreted as exploratory given the limited sample size. Conclusions: STA-MCA bypass was associated with significant increases in semi-quantitative perfusion area on SPECT, particularly in the basal ganglia. The lack of ipsilateral–contralateral difference is consistent with a possible global hemodynamic effect, but this interpretation remains hypothesis-generating. The pragmatic SPECT method is feasible for perioperative monitoring yet requires further validation. Larger prospective studies with standardized protocols are warranted.