OBJECTIVE AND IMPORTANCE:Idiopathic spinal cord herniation (ISCH) is a rare condition, reported in only 25 patients thus far, in which the thoracic cord is prolapsed through an anterior dural defect. It typically presents in middle age as either Brown-Séquard syndrome or spastic paraparesis.CLINICAL PRESENTATION:A 55-year-old woman initially presented at the age of 41 years with Brown-Séquard syndrome at the T8 disc space level on the left side. Investigations, including primitive magnetic resonance imaging, were deemed negative at that time. After a stepwise deterioration over 14 years, she presented again with spastic paraparesis and double incontinence, in addition to her previous spinothalamic dysfunction. Magnetic resonance imaging at this stage suggested either ISCH or a dorsal arachnoid cyst.INTERVENTION:Through a T7-T8 laminectomy, a left-of-midline ISCH was identified and easily reduced by gentle cord traction. No dorsal arachnoid cyst was identified. The anterior dural defect was repaired with a XenoDerm patch (LifeCell Corp., Woodlands, TX). After surgery, there was improved motor and sphincter function. However, there was continued sensory disturbance.CONCLUSION:ISCH is rare cause of thoracic cord dysfunction. Despite prolonged diagnostic delay, significant clinical improvement may be obtained with ISCH reduction and anterior dural repair.