Infectious Arachnoiditis

43-year-old male who presents with acute onset altered mental status, photophobia, and low back pain. On the fluid sensitive sequences, there is ill-defined thickening of the cauda equina conus medullaris. These findings are confirmed on the postcontrast images which demonstrate symmetric smooth circumferential thickening of the cauda equina as they descend to the respective neural foramen. Further imaging of the brain demonstrate numerous peripherally enhancing parenchymal abscesses, one of which was communicating with the occipital horn on the right with associated ventriculitis and pus filling the dependent portions of the supratentorial ventricular system. The findings within the lumbar spinal region are compatible with acute infectious arachnoiditis. Clinical symptoms of lumbar arachnoiditis include leg pain, sensory changes, and motor weakness. Imaging features include thickening of the nerve roots with possible clumping and tethering to the surrounding dura resulting in an empty thecal sac sign.