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

Abstract

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.

Keywords: dural defect; magnetic resonance imaging; medullary herniation; spinal cord; thoracic myelopathy.

Figure 1

Preoperative MRI studies obtained in the thoracic spine of a 56-year-old woman who presented with a Brown-Séquard syndrome (case 4). (A) sagittal T2-weighted image shows that the spinal cord is ventrally dislocated in the spinal canal at the level of T5 with a spacious CSF volume posteriorly. (B) axial T2-weighted image at the level of T5 demonstrating a ventral adhesion with soft tissue outside the dura strongly indicating herniation of the spinal cord.

Figure 2

Intraoperative ultrasound image shows a ventral herniation of the spinal cord (arrow) and enlargement of the dorsal subarachnoid space.

Figure 3

Intraoperative view: (A) before surgical reduction shows the ventral spinal cord incarcerated in a sharp oval dural defect. (B) the herniated lobule has been reduced against the major cord surface, but the lobule does not flatten into the cord. (C) a synthetic dural patch has been placed ventral to the spinal cord and secured with stitches on both sides.

Figure 4

Postoperative MRI: (A) sagittal and (B) axial T2-weighted images of the thoracic spine demonstrate realignment of the spinal cord and restoration of CSF ventral to the spinal cord (case 5). At 12-months follow-up the patient was clinically improved.

Figure 5

Postoperative MRI: (A) T2-weighted sagittal and (B) axial images show a persistent intramedullary hyperintensity at 12-months follow-up in a patient with no clinical change after surgery (case 2).