Anomalous location of the vertebral artery in relation to the neural foramen. Implications for cervical transforaminal epidural steroid injections.

OBJECTIVES Evaluate the prevalence of an anomalous posterior vertebral artery (VA) in the neural foramen and to see if any factors might correlate with proximity of the VA to needle location in a cervical transforaminal epidural steroid injection (CTFESI). METHODS A radiologist with subspecialty training in neuroradiology documented VA location in relation to the neural foramen on axial views of 198 consecutive computed tomography angiograms done for various reasons, 11 were excluded because of poor imaging or occluded VA. The levels of C2-3 through C6-7 were evaluated, where the VA courses within the foramen. The distance was measured from VA to ideal needle location for a CTFESI. Other data were collected including severity of foraminal stenosis, loss of disc height, and medical history. Analysis was done to see if any factor correlated with anomalous VA location. RESULTS The VA was in the posterior foramen and within 2 mm of ideal needle location in at least one location in 29% of patients. When looking at the more commonly injected levels of C4-5 through C6-7, the prevalence was 18%. Severity of foraminal stenosis and loss of disc height correlated with VA proximity to typical needle location (both with P < 0.0001). CONCLUSION The VA can sometimes be in close proximity to the typical target location of a CTFESI. This proximity correlates with severity of foraminal stenosis and loss of disc height. Physicians should be mindful of this and evaluate the T2 axial magnetic resonance imaging before doing CFTESIs.