Question: Which code should I report for MRI lumbar plexus? Texas Subscriber Answer: Here's why: Lumbar MRI codes 72148, 72149, and 72158 (Magnetic resonance [e.g., proton] imaging, spinal canal and contents, lumbar...) specify "spinal canal," which is the space in the vertebrae the spinal cord passes through. The lumbar plexus is a nerve network situated in the posterior part of the psoas muscle and in front of the lumbar vertebrae transverse processes, which are bone projections muscles attach to. So the lumbar spinal canal codes aren't appropriate for a lumbar plexus MRI. The lumbar region is between the diaphragm and the pelvis, so codes 72195-72197 (Magnetic resonance [e.g., proton] imaging, pelvis ...) also would not be correct.