Fractional anisotropy quantification by diffusion tensor MRI of cranial nerves VII and VIII with neurovascular contact in patients with and without neurocompressive syndrome

M. Pilar Cortes-Avalos, Magnetic Resonance Imaging Unit, Institute of Neurobiology, Universidad Nacional Autonoma de Mexico, Juriquilla, Queretaro, Mexico;
C. Arturo Dominguez-Frausto, Magnetic Resonance Imaging Unit, Institute of Neurobiology, Universidad Nacional Autonoma de Mexico, Juriquilla, Queretaro, Mexico;
Juan A. Benitez-Lopez, Magnetic Resonance Imaging Unit, Institute of Neurobiology, Universidad Nacional Autonoma de Mexico, Juriquilla, Queretaro, Mexico;

Introduction: Fractional anisotropy (FA) quantification using diffusion tensor imaging (DTI) provides information beyond anatomy. It allows differentiation between incidental asymptomatic neurovascular contact (NVC) and clinical neurocompressive syndrome. This study evaluated the FA of cranial nerves VII and VIII with NVC at the cerebellopontine angle in patients with and without neurocompressive syndrome. Material and Methods: This cross-sectional study evaluated participants with and without neurocompressive syndromes, including hemifacial spasm, tinnitus, or vertigo. Conventional 3.0T magnetic resonance imaging (MRI) with T2-weighted CUBE and 3D- time-of -flight (TOF) sequences was performed. FA quantification using DTI MRI, as well as Chavda type and Gorrie grading were used to assess NVC. Results. We evaluated 132 ears in 66 adults; 99 (75.0%) had some type of NVC. Among these, 66 ears were asymptomatic with a high mean FA (0.294 ± 0.068). Thirty-three ears with neurocompressive syndrome had a low mean FA (0.218 ± 0.053) (p < 0.001). In ears with NVC, the mean FA was 0.207± 0.032 in hemifacial spasm (n = 6, 6.1%), 0.227 in tinnitus (n = 21, 21.2%), and 0.206 in vertigo (n = 14, 14.2%). In contrast, the mean FA was 0.273 in ears without hemifacial spasm (n = 93, 93.9%), 0.280 in those without tinnitus (n = 78, 78.8%), and 0.279 in those without vertigo (n = 85, 85.8%). FA differences were significant between ears with and without neurocompressive syndrome. Conclusion. DTI MRI demonstrated significantly lower FA of cranial nerves VII and VIII with NVC at the cerebellopontine angle in ears with neurocompressive syndrome compared to asymptomatic ears with NVC.

Keywords: Diffusion tensor. Fractional anisotropy. Neurovascular contact. Neurocompression syndrome. Facial nerve. Vestibulocochlear nerve.