Differential CT diagnosis of extruded nucleus pulposus.

The detection and differential diagnosis of extruded (free) disk fragments by CT has not been described in detail. We reviewed the lumbar CT scans of 57 patients with extruded disk fragments and of 31 patients in whom the CT appearance of disk fragments was simulated by other processes. An extruded disk fragment commonly appears on CT scans as an epidural mass that must be distinguished from either an epidural tumor or an anomalous root sheath. A normal posterior disk margin does not exclude a disk herniation when the nuclear fragment is extruded. Free disk fragments can be differentiated from root-sheath anomalies and tumors in most cases by measuring tissue densities and analyzing adjacent bone.