Posterior epidural migration of lumbar disk fragments: report of two cases and review of the literature.

BACKGROUND: Posterior epidural migration of an extruded disk fragment is rare, and posterior migration of the free fragments causing cauda equina syndrome is exceptionally rare. The disk fragment must transgress through numerous anatomical restraints including the nerve roots in such cases.
METHODS: Two cases of migration of the sequestrated disk into the posterior epidural space are presented. The first patient complained, over the course of 1 month, of paresthesias and weakness of the lower limbs, with urinary retention. However, in the other case, there was steppage gait and strength score of 3/5 on dorsiflexion of left foot, without bladder or bowel disturbance.
RESULTS: Lumbar CT scan with sagittal reconstruction showed a posterior epidural mass, which was isodense to the disk. The preoperative differential diagnosis included epidural abscess, hematoma, and neoplasm. An urgent decompressive lumbar laminectomy was performed. At surgery, the lesion proved to be a massive extruded disk fragment.
CONCLUSION: Diagnosis of posterior epidural migration of the sequestrated disks may be difficult. It may present with subtle clinical features. Magnetic resonance images may mimic those of other more common posterior epidural lesions. Early surgery should be the first choice to prevent severe neurologic deficits.