- General indications for ESI include herniated disk disease with or without radicular pain, spinal stenosis, axial low back pain, and post–lumbar surgery syndrome.
- With an interlaminar ESI, a single line and a well-defined or smudged convexity along the spinolaminar line on the lateral view suggest that the needle tip is positioned correctly in the epidural space. On the AP view, contrast agent dispersion with drug injection may outline exiting spinal nerves.
- With a transforaminal ESI, if the needle tip is in the true epidural space, a test dose of contrast agent will flow upward (occasionally downward) along the medial margin of the pedicles and along the exiting nerve.
- With an intradural injection, contrast material rapidly disperses and accumulates at the ventral portion of the spinal canal, forming a cerebrospinal fluid–contrast agent level (dorsal cerebrospinal fluid and ventral contrast material) because of the patient’s prone position. The AP view demonstrates a symmetric distribution of contrast material, similar to that seen at myelography.
- At imaging, intraepineural injection manifests as two thin lines resembling a so-called tram track, with a subtle feathery appearance inside the nerve root and sharp outlines.