Imaging of idiopathic spinal cord herniation.

Idiopathic spinal cord herniation, unlike spinal cord herniation with a known traumatic or postoperative origin, is a relatively rare condition; however, it has been diagnosed and reported with increasing frequency in recent years. Such herniation most often occurs in the thoracic spine, between the T4 and T7 vertebrae. Brown-Séquard syndrome is the most frequently reported clinical feature. Early manifestations may include numbness and decreased temperature sensation in the legs, gait disturbances, pain, and incontinence. Symptoms often worsen over time, but timely diagnosis and treatment may allow the reversal of neurologic deficits. Surgical reduction typically is performed in patients with a history of symptom progression, but patients whose symptoms are less severe may be eligible for less invasive therapy and monitoring. Imaging features of spinal cord herniation generally include a dural tear through which a portion of the cord protrudes. Cerebrospinal fluid flows freely through the defect, causing increased turbulence in the fluid just dorsal to the site of herniation. The observation of this feature may allow the differentiation of spinal cord herniation from an arachnoid cyst. In addition, the calcification of nucleus pulposus leakage from a herniated disk may produce a linear area of hyperattenuation at computed tomography or signal hyperintensity at magnetic resonance imaging, an imaging feature known as the "nuclear trail" sign. (c) RSNA, 2008