The lumbar CT horizontal sections identification requires three levels to be defined of each vertebra: The arthropedicular level (upper third) describes an (omega) at the back with its dense bone structures. At each side of the canal is the upper part of the lateral recess, the narrowest and therefore the most threatened part of the nerve root passage. The isthmopedicular level (middle third) describes a complete bone ring around the vertebral canal. On this non articular level, the congenital dysplasia is most clearly observed. The subpedicular level (lower third) with its muscular surrounding, shows a floral outline. A fourth level, intervertebral or discal, is added. It is very similar to the last one and of course is the most common point of disco-radicular conflict. Each level appears to be specific, both by the silhouette outlined by the ligament and bone structures and by the relationship which they have with the meninges. Each of them has its own pathology which precisely directs the surgical approach.