Idiopathic ventral spinal cord herniation: an increasingly recognized cause of thoracic myelopathy.

Idiopathic spinal cord herniation (ISCH), where a segment of the spinal cord has herniated through a ventral defect in the dura, is a rarely encountered cause of thoracic myelopathy. The purpose of our study was to increase the clinical awareness of this condition by presenting our experience with seven consecutive cases treated in our department since 2005. All the patients developed pronounced spastic paraparesis or Brown-Séquard syndrome for several years (mean, 4.7 years) prior to diagnosis. MRI was consistent with a transdural spinal cord herniation in the mid-thoracic region in all the cases. The patients underwent surgical reduction of the herniated spinal cord and closure of the dural defect using an artificial dural patch. At follow-up, three patients experienced considerable clinical improvement, one had slight improvement, one had transient improvement, and two were unchanged. Two of the four patients with sphincter dysfunction regained sphincter control. MRI showed realignment of the spinal cord in all the patients. ISCH is probably a more common cause of thoracic myelopathy than previously recognized. The patients usually develop progressive myelopathy for several years before the correct diagnosis is made. Early diagnosis is important in order to treat the patients before the myelopathy has become advanced.