This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cerebrovascular Diseases, Subject name: Surgery
[{'content': '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? \nSelect and explain. \nA. A lesion at the right L4-L5 interspace, B. Pathology where the nerve exits the spinal canal immediately above the pedicle of S3 veebra, C. A herniated nucleus pulposus, D. Compression by the L5 lamina', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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', 'role': 'assistant'}]