Other entities to consider in this category are:
Redundant Nerve Roots
Flow Artifact Mimicking Abnormal Vascularity
Unusual entity
AV fistula to cervical epidural venous plexus in patients with NF-1
https://www.ncbi.nlm.nih.gov/pubmed/16876638
(I saw case as an embo fellow at NYU with Alex Berenstein)