Idiopathic spinal cord herniation: a new theory of pathogenesis.

BACKGROUND Idiopathic spinal cord herniation is a rare entity that has been described more frequently over the past few years. Its pathophysiology remains obscure, however. METHODS We report a case of spinal cord herniation and review the literature extensively. In view of our review, we try to determine the clinical features of the condition and the diagnostic measures used, with emphasis on the role of magnetic resonance (MR) phase-contrast CSF study. The factors affecting the outcome of the condition are also studied including time and type of presentation, as well as the surgical procedure performed. The pathophysiological mechanisms behind spontaneous herniation are discussed, and a new hypothesis is proposed. RESULTS Idiopathic spinal cord herniation occurs in the middle-aged adult, with a preponderance of patients being female. Brown-Séquard syndrome is the most common clinical presentation and usually progresses to spastic paraparesis. MRI typically shows a ventral kink in the thoracic cord, with MR phase-contrast imaging proving an important addition to exclude an arachnoid cyst. Better outcomes were noted in the patients treated earlier, and in those with no spasticity. Widening the dural defect seems to afford better results compared to grafting of the defect. The prognosis is favorable after correction, though a vertebral body herniation variant may be associated with worse outcome. In view of the chronology of events and imaging studies in our patient, we hypothesize that herniation occurs as an acquired phenomenon where an inflammatory process results in adherence between the spinal cord and the dura, with erosion, formation of a dural defect, and then later herniation occurring with cerebral spinal fluid (CSF) pulsations. CONCLUSIONS Idiopathic herniation of the spinal cord should be recognized and treated early to reach a favorable outcome. It seems to be an acquired condition likely caused by an inflammatory event, the nature of which is to be determined.