Pontine Microtubular Signal Intensity in Hemifacial Spasm: Association with Outcome After Microvascular Decompression Surgery

BACKGROUND: We aimed to investigate the prevalence and clinical significance of pontine microtubular signal intensity (MSI), presumed dilated perivascular or perineural spaces, in patients with hemifacial spasm (HFS) using high-resolution MRI using proton density-weighted imaging (HR-PDI). METHODS: We retrospectively analyzed 438 patients with unilateral HFS who underwent microvascular decompression (MVD) and preoperative HR-PDI. MSI was defined as a linear or curvilinear hyperintense lesion along the presumed course of the intraparenchymal facial nerve fascicles within the pons on HR-PDI. The presence and laterality of MSI were evaluated by consensus between two reviewers and classified according to their relationship to the symptomatic side of HFS as ipsilateral (same side as the facial spasm), contralateral (opposite side), or bilateral. Clinical characteristics, surgical findings, and postoperative outcomes were compared according to the presence of ipsilateral MSI. A control group of 307 subjects who underwent HR-PDI for non-central neurologic symptoms was included to assess the prevalence of MSI. Multivariable logistic regression analysis was performed to identify factors associated with immediate postoperative improvement after MVD. RESULTS: = 0.005). However, long-term surgical outcomes were not significantly different according to the presence of MSI. CONCLUSIONS: Pontine MSI on HR-PDI is more frequently observed in patients with HFS and is associated with a lower likelihood of immediate postoperative improvement and a tendency toward delayed recovery after MVD but not with poorer long-term outcomes. These findings suggest that MSI may represent microstructural or neurofluidic alterations along the pontine facial nerve pathway and may serve as an imaging marker of delayed recovery dynamics.