Hydromyelia is an abnormal widening of the central canal of the spinal cord. This widening creates a cavity in which cerebrospinal fluid may accumulate, resulting in abnormal pressure on the spinal cord. Hydromyelia is associated with a number of disorders that disrupt the normal flow of cerebrospinal fluid, including Chiari I and II and Dandy-Walker malformation, and is often associated with trauma. Symptoms, which may not occur immediately, include weakness of the hands, arms, and legs, and sensory loss in the neck and arms. Some individuals have severe pain in the neck and arms. Diagnosis is made by magnetic resonance imaging (MRI) and electromyography.