<prompt> A 48-year-old woman has a lower back pain and hypoesthesia in the left S1 dermatomal distribution left calf and lateral left foot. What is the most likely cause?A lesion at the right L4-L5 interspacePathology where the nerve exits the spinal canal immediately above the pedicle of S3 veebraA herniated nucleus pulposusCompression by the L5 lamina  <response>: Thoracic, lumbar, and sacral nerves exit off the spinal canal immediately below the pedicle of the corresponding numbered veebra. The left S1 root, for example, passes immediately dorsal to the L5-S1 disc where it can be susceptible to compression by a herniated nucleus pulposus. The root then swings laterally to exit immediately caudal to the left L5 pedicle. For a correlation between level of disc herniation and the root affected, see the table below. Level of Herniation Root Affected L1-L2 L2 L2-L3 L3 L3-L4 L4 L4-L5 L5 L5-S1 S1 