Review Question - QID 214321

A 7-year-old boy presents to the emergency department for a fever and back pain for the past several days. It has been gradually worsening and does not respond to ibuprofen or acetaminophen. The mother thinks the pain started the day after the child was helping his father move boxes in the basement. The child says moving makes the pain worse. The child was born at home and sees a chiropractor as his primary doctor. His temperature is 97.0°F (36.1°C), blood pressure is 110/61 mmHg, pulse is 100/min, respirations are 25/min, and oxygen saturation is 100% on room air. Physical exam reveals pain over the child's lumbar spine, pain with bending over, and pain with the straight leg test on both sides. An MRI is performed as seen in Figure A. Which of the following is the most likely diagnosis?