Longitudinal ligaments of the lumbar spine

The diagnosis of disruption of the posterior longitudinal ligament in disk herniation is important in deciding between surgical or percutaneous management of HNP. The normal ligaments studied on spine specimens are better seen on long repetition time (TR), short echo time (TE) images and appear as linear structures with very low signal intensity on all pulse sequences surrounding the outer anulus. The authors prospectively imaged 20 HNPs in 18 patients who underwent surgery. In eight cases, the posterior longitudinal ligament was seen intact around the HNP on both short TR, short TE and long TR, short TE images. All were subligamentous at surgery. MR imaging demonstrated disruption of the longitudinal ligament in ten cases because of interruption, absence around the disk fragment, or interposition between disk and fragment. The ligament was disrupted at surgery in only eight of these cases. The two false-positive images showed a pseudointerruption related to a chemical shift antifact. The two remaining studies were qualified as questionable. The overall sensitivity of MR imaging was 100%, and its specificity was 77%