Objective        To analyze the clinical and magnetic resonance imaging (MRI) manifestations of Hirayama disease for improving diagnostic accuracy.       Methods       Clinical

electromyography and MRI data of 13 male patients were reviewed retrospectively. Cervical spine MRI scanning included plain scanning in both neutral and flexed positions

contrast enhancement scanning and diffusion tensor imaging (DTI) (3 cases).       Results       Progressive muscular weakness and atrophy of unilateral or bilateral distal u

pper extremities were the main manifestations of the 13 patients. The results of electromyography presented neurogenic damage in the involved muscles. MRI manifestations on neutral position showed: ① Cervical array and curvature were abnormal

and cervical intervertebral discs degeneration

bulging and protrusion were also observed in all patients. ② Atrophic and flattening spinal cord was mainly located in lower cervical segments on the axial position

and the affected segments in 7 patients presented abnormal intramedullary high signal that was the same as ischemia

necrosis and mild proliferation of glial cells. MRI findings on flexed position showed: ① Lower cervical dural sac shifted forward and compressed the corresponding segments of spinal cord in all patients

and an obvious dilation was observed in posterior epidural space. Small round and curvilinear flow void signal in the dilated epidural space was observed in 9 patients. ② Strong homogeneous enhancement of posterior epidural space on the post contrast flexion position imaging was observed in 3 patients. ③ DTI in 3 patients showed that the ADC value of the lesions increased and the FA value decreased. The number of nerve fiber tracts in 2 patients became fewer in the atrophic segments

and the disruption of the nerve fiber tracts was observed in the malacia lesion on T

2

WI in 1 patient.       Conclusion       There are some characteristics of Hirayama disease in both MRI and clinical manifestations

especially in dynamic position MRI. DTI may provide quantitative evaluation and be helpful for the diagnosis and prognosis of Hirayama disease.