title: Flatness of the infratentorial space associated with hemifacial spasm.
abstract: Whether a difference in morphology of the infratentorial space is associated with hemifacial spasm is not well understood. The aim of this study was to analyze the three-dimensional conformation of the infratentorial space and evaluate any possible contribution of morphological characteristics to the development of neurovascular compression leading to hemifacial spasm.
  
  
  
  We enrolled 25 patients with hemifacial spasm and matched them by age and sex to controls. The extent of the three-dimensional axes and the volume of the infratentorial space were measured using image analysis software for three-dimensional MRI. We evaluated the correlation between a morphological difference in the infratentorial space and changes in vascular configuration in the brain stem.
  
  
  
  We found no statistical difference in volumetric analyses. The mean aspect ratio on the coronal plane (the ratio of the Z to X extent) of the infratentorial space in patients with hemifacial spasm was significantly lower (p < 0.01) than that in controls, as was the mean aspect ratio on the sagittal plane (the ratio of Z to Y extent, p < 0.01). A smaller sagittal aspect ratio was correlated (p < 0.05) with greater lateral deviation of the basilar artery.
  
  
  
  Our results suggest that flatness of the superior-inferior dimension of the infratentorial space is an anatomical feature that characterizes patients with hemifacial spasm. We hypothesize that this unique structural variation may exaggerate the lateral deviation of the vertebrobasilar arteries due to arteriosclerosis and exacerbate the space competition among vessels and cranial nerves.
authors.affiliation: Department of Neurosurgery, Kumamoto University Medical School, 1-1-1, Honjo, Chuo-ku, Kumamoto, 860-8556, Japan. thamasaki-nsu@umin.ac.jp.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Hamasaki
authors.affiliation: Department of Neurosurgery, Kumamoto University Medical School, 1-1-1, Honjo, Chuo-ku, Kumamoto, 860-8556, Japan.
authors.forename: Kazumichi
authors.initials: K
authors.lastname: Yamada
authors.affiliation: Department of Diagnostic Radiology, Kumamoto University Medical School, 1-1-1, Honjo, Chuo-ku, Kumamoto, 860-8556, Japan.
authors.forename: Mika
authors.initials: M
authors.lastname: Kitajima
authors.affiliation: Department of Neurosurgery, Kumamoto University Medical School, 1-1-1, Honjo, Chuo-ku, Kumamoto, 860-8556, Japan.
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Kuratsu
mesh_terms: D000328:Adult; D000368:Aged; D050197:Atherosclerosis / Q000150:complications*; D001488:Basilar Artery / Q000000981:diagnostic imaging* / Q000473:pathology; D001933:Brain Stem / Q000098:blood supply / Q000000981:diagnostic imaging; D005260:Female; D019569:Hemifacial Spasm / Q000000981:diagnostic imaging* / Q000209:etiology / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged
keywords: Hemifacial spasm; Magnetic resonance imaging; Morphometry; Neurovascular compression syndrome