Low density in the posterior portion of the lumbar disk: a new CT finding in disk herniations.

The author describes a new computed tomographic finding associated with disk herniation--a low density in the posterior aspect of the disk, usually having a crescentic shape. This low density probably represents an area of fluid or blood accumulation within the annulus fibrosus caused by tearing of fibers in the annulus and an associated injury to the adjacent cartilage plate which opens into the spongiosa. Observation of this finding should support the diagnosis of a herniated nucleus pulposus.