Posterior Epidural Migration of an Extruded Lumbar Disc Fragment Causing Cauda Equina Syndrome

Study Design. Retrospective case report. Objectives. To illustrate the rare occurrence of cauda equina syndrome resulting from posterior epidural disc fragment migration documented by magnetic resonance imaging. Summary of Background Data. Disc fragment migration patterns are generally limited by the attachments of the posterior longitudinal ligament and its associated "midline septum" and "peridural" or "lateral membrane." The majority of symptomatic lumbar disc herniations are noted to be in a lateral position with resultant nerve root irritation. Although caudal, rostral, and lateral migration of disc fragments are common, posterior epidural migration of an extruded disc fragment has been reported only rarely, and only once in association with cauda equina syndrome. Methods. The patient described in this report presented with an acute cauda equina syndrome. Investigation with magnetic resonance imaging revealed a posterior epidural mass, which was hypointense on T1-weighted and T2-weighted images. Postgadolinium imaging showed rim enhancement of the lesion. The preoperative differential diagnosis included epidural abscess, hematoma, or neoplasm. An urgent decompressive lumbar laminectomy was performed. At surgery, the lesion proved to be a massive extruded disc fragment. Results. At the 1-year follow-up examination, the patient had recovered full motor, sensory, urologic, and sexual function. Conclusions. Extruded disc fragments may migrate posterior to the thecal sac. Magnetic resonance images of a posterior disc fragment may mimic those of other more common posterior epidural lesions.