To report a rare case of superficial siderosis of the cauda equina roots detected by high field MRI.

Susceptibility weighted imaging (SWI) is a MRI technique that is very sensitive to compounds which cause magnetic field distortion in living tissues, including iron and calcium. SWI, which is derived from gradient-recalled echo (GRE) sequences, has significantly higher sensitivity for hemosiderin deposition.

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A 60-year-old man with a history of traumatic brain injury (TBI) with subdural hemorrhage presented with abnormal gait and urinary urgency that began shortly after his TBI. Exam showed sensory ataxia with impaired vibration in bilateral lower extremities, impaired temperature in the right lower extremity, mild weakness of left foot extension, and normal reflexes. Initial MRI of the lumbar spine showed thickening and diffuse post-contrast enhancement of the cauda equina roots. CSF studies revealed albuminocytologic dissociation (white blood cells 2, protein 82 mg/dL), which led to suspicion for chronic inflammatory demyelinating polyneuropathy (CIDP). However, the EMG/NCS study was normal. Given the concern for an inflammatory vs chemical process, a special MRI of the lumbar spine with highly sensitive multiecho SWI sequences was obtained. It re-demonstrated prominent cauda equina nerve roots with decreased post-contrast enhancement. Furthermore, it showed susceptibility artifact around the nerve roots, consistent with hemosiderin deposition.

Superficial siderosis at the cauda equina nerve roots and CIDP may have similar clinical presentations, and post-contrast root enhancement on MRI of the spine may not be able to differentiate between the two. The new application of advanced imaging technique of 3T MRI with SWI sequences may help detect hemosiderin deposition and therefore allow to make the diagnosis of superficial siderosis at the nerve root level, a likely under-detected and previously unreported condition based on our reference research.