Spondylolysis, spondylolisthesis, and associated nerve root entrapment in the lumbosacral spine: MR evaluation.

Spondylolysis is defined as a bone defect in the pars interarticularis. Its cause is uncertain but is believed in most cases to be related to repeated stress, trauma, or both. Findings of spondylolysis on conventional radiographs and on CT scans have been well characterized. Although these imaging techniques remain effective for the diagnosis of this defect, MR imaging is increasingly used as the primary or sole imaging method in patients with lower back pain and radiculopathy. Therefore, because MR images of the lumbar spine may be interpreted in the absence of correlative CT scans or conventional radiographs, the MR features of spondylolysis and its associated findings must be recognized. This essay illustrates the MR findings of lumbosacral spondylolysis and associated entrapment and direct impingement of the spinal nerve root.