Magnetic resonance imaging in Hirayama disease.

Hirayama disease (HD) is a rare type of cervical myelopathy related to flexion of the neck characterized by progressive muscular weakness and atrophy of the distal upper limbs most frequently seen in young males. HD is thought to be secondary to an abnormal anterior displacement of the posterior dura with secondary compression of the lower cervical spinal cord and chronic injury to the anterior gray matter horns. We present two patients with HD and discuss its pathophysiology and imaging characteristics.