Posttraumatic syringomyelia: profound neuronal loss, yet preserved function.

Posttraumatic syrinxes may extend many cord segments rostral to a spinal cord injury (SCI) and significantly dilate the spinal cord, yet few neurologic deficits may be noted. Careful physical examination may reveal ascending loss of pain and temperature without evident functional motor decline. We present a 49-year-old man with T4 paraplegia and a large posttraumatic syrinx who died 3 weeks after syringoperitoneal shunting. Neuropathologic study revealed a large bilateral syrinx cavity from T1 to C6 that tapered to a small unilateral syrinx at C2. Light microscopy of sections from T1 to C2 showed massive loss of intermediate to intermedio-lateral gray neurons and moderate reduction of motoneurons at T1 to C6 levels. Despite these findings, manual muscle testing results remained normal for wrist extensors and elbow extensors, and the patient continued to perform independent sliding board transfers. We conclude that this large progressive syrinx did not merely dissect neural elements apart but caused extensive neuronal damage. Loss of interneurons was evident in spinal segments with preserved strength and function. Possible mechanisms to explain the relatively minimal clinical deficits in view of the neuronal loss are discussed.