Aim:The latency of spread refers to the time interval between the onset of the orbicularis oculi muscle and the involvement of lower facial muscles, which varies among patients with typical hemifacial spasm. In this study, we aimed to investigate whether the latency of spread could reflect the complexity level of intraoperative offending vessels. Material and Methods:A total of 96 patients with typical hemifacial spasm who underwent microvascular decompression (MVD) in our department between August 2018 and December 2019 were retrospectively analyzed. We introduced a new concept of three complexity levels of offending vessels based on six vascular classifications proposed by Kwan Park et al. and the difficulty of intraoperative management reviewed by surgical videos. One-way analysis of variance, Spearman correlation analysis, and multivariate linear regression analysis were performed.Results: There were significant differences in latency of spread among the three complexity levels of offending vessels (p < 0.01). Spearman correlation analysis showed a strong negative correlation between vascular complexity level and the latency of spread (r = -0.7997, p < 0.0001). Multivariate linear regression analysis showed that the vascular complexity level was the main factor affecting the latency of spread (p < 0.01). In contrast, other factors such as sex, side, age, hypertension, and diabetes had no significant effects.Conclusion:As an important clinical indicator, the latency of spread can reflect the complexity level of offending vessels in patients with typical hemifacial spasm before MVD.