In one systematic review comparing transforaminal, interlaminar, and caudal ESIs, the authors concluded that there was moderate evidence for long-term (>6 weeks) relief of lumbar radicular pain using the transforaminal and caudal approaches, but limited evidence using the interlaminar approach (30). The authors also concluded that there was moderate evidence for relief of cervical nerve root pain using both the transforaminal and interlaminar approaches (30). Another study concluded that the transforaminal approach was more effective than the interlaminar or caudal approaches in treating lumbar pain (31). A review showed transforaminal lumbar ESIs under fluoroscopic guidance to be more cost effective than blind interlaminar and caudal ESIs (32).
As of this writing, no peer-reviewed, randomized controlled studies have compared transforaminal and interlaminar ESIs in the thoracic region.
For lumbar transforaminal epidural injection (TEI), the patient is placed in a prone position with a pillow or abdominal roll under the abdomen to at least reduce and ideally reverse the lumbar lordosis in order to open up the foramen. Using an ipsilateral oblique fluoroscopic view, the x-ray tube (source) of the C-arm fluoroscope is generally angulated in either a caudal direction (for L5-S1 and L4-5 TEI) or cephalic direction (for L3-4 and above TEI) to square the inferior endplate of the vertebral body, and to place the superior articular process of the subjacent segment pointing at 6 o’clock of the pedicle of the above level that appears as a Scottie dog eye. Local skin is then prepped and draped in a sterile manner. A local skin wheel is raised with 1% lidocaine at the needle entry site and the subcutaneous tissue in the needle trajectory path is infiltrated with 1% lidocaine. A 22- or 25-gauge spinal needle of appropriate length is inserted and directed down and parallel to the fluoroscopic beam toward the “safe triangle.” The safe triangle is formed by the lower border of the pedicle, the lateral margin of the vertebral body, and the traversing nerve root. To avoid deep needle placement and potential injury to the vasculature or nerve root or DRG in the neuroforamen, the novice injectionist should advance the needle until the needle tip touches the lower edge of the Scottie dog eye, the junction of the transverse process and the superior articular process. The needle is then slightly withdrawn for 2 to 3 mm and redirected inferiorly just under the lower edge of the transverse process for about 0.5 mm. Further advancement of the needle should be under AP and cross table (lateral) views. The final needle tip position should be at the posterior half of the neuroforamen just under the pedicle in the lateral view to minimize the potential injury to the vasculature, nerve root, or DRG. In the AP view, the needle tip should not be medial to the medial edge of the pedicle to avoid penetrating the dura mater. For S1 transforaminal injections, the eye of the Scottie dog can also be used as an injection landmark. Using a slightly caudad and ipsilateral fluoroscopic view, the S1 Scottie dog image is outlined. The needle should be directed to the outer upper quadrant of the neuroforamen. In the lateral view, the needle tip should not pass the anterior margin of the sacral canal that appears as a radiological lucent strip. A neurogram pattern should then be visualized under an AP view (Fig. 68-4).
FIGURE 68-4. Left L5-S1 TEI. AP view showing a neurogram pattern of left S1 and L5 nerve roots.
For the L5-S1 foramen, the C-arm source often needs to be tilted in a caudad direction to accommodate any remaining lumbar lordosis. An ipsilateral oblique projection is then used to visualize the Scottie dog and the target is identified as the region immediately under the pedicle, slightly lateral to the 6 o’clock position (Fig. 68-5). This position leads to needle placement in the neuroforamen, ventral to the nerve root. Lateral imaging is used to demonstrate the needle depth, which should be located at the superior portion of the intervertebral foramen, just under the pedicle (Fig. 68-6). An AP view is then obtained to ensure that the needle tip is located at the “safe triangle,” slightly lateral to the 6 o’clock position of the pedicle. The safe triangle is formed by the lower border of the pedicle, the lateral margin of the vertebral body, and the traversing nerve root. A needle position located within the safe triangle and lateral to the 6 o’clock position is deemed safe because it will not penetrate the nerve, blood vessels, or dura mater. Nevertheless, because of the precarious location of the nerve root and the DRG, caution should be exercised by advancing the needle slowly upon entering the neuroforamen, to avoid needle penetration of these neurologic structures. If the patient complains of radicular pain or paresthesias, the needle should be withdrawn and redirected superiorly. Once the needle is deemed at the proper position, approximately 1.0 mL of the contrast is injected under live fluoroscopic view. The needle should be redirected if there is vascular uptake of the contrast. The injected contrast should ideally outline the nerve root and also show epidural spread. Three milliliters of a mixture of solution containing 40 to 125 mg of preservative-free methylprednisolone, 6 to 9 mg of preservative-free betamethasone sodium phosphate, 40 to 50 preservative-free triamcinolone (33,34), or other equivalent dose of preservative-free corticosteroid and preservative-free 1% lidocaine can be slowly injected into the neuroforamen through the spinal needle (25,26).
FIGURE 68-5. L5-S1 and S1 TEI. Oblique view showing needle just under the 6 o’clock position of the L5 pedicle and outer lateral quadrant of S1 for L5 and S1 TEIs respectively.
FIGURE 68-6. Lumbar L5-S1 and S1 TEIs. Lateral view demonstrating contrast in the ventral epidural space. Theoretically, the transforaminal approach should achieve more anterior flow of the injectate than would be typical for an interlaminar approach.
A thoracic TEI is performed with the patient in a prone position. The fluoroscope should be directed in a similar fashion as for lumbar TEI. A critical part of the injection is the correct identification of a clear rectangular-shaped clear space window under the fluoroscope. The upper and lower borders of the rectangle are the lower edge of the lamina of the same vertebral segment and the upper edge of the inferior vertebral endplate of the same segment. The lateral and medial borders of the rectangle are the medial edge of the rib head and the pars interarticularis of the same segment, respectively. After proper skin preparation and local anesthesia, the spinal needle is inserted and directed toward the lower edge of the Scottie dog eye using the same technique as in the lumbar TEI. Caution should be exercised not to direct the needle outside the clear rectangle window. If the needle strays too far laterally outside the rectangular window, it can penetrate the pleura, resulting in a pneumothorax. Needle placement too medially outside the rectangular window can result in spinal cord injury. The final needle position should be in the posterior half of the neuroforamen in the lateral view and the 6 o’clock position of the pedicle in an AP view. The contrast and corticosteroid are injected in a similar fashion as when performing a lumbar TEI.
A cervical TEI is performed, with the patient in a supine position and the head turned to the contralateral side. A peripheral intravenous line should be placed, and vital signs, as well as oxygen saturation, should be monitored. The C-arm fluoroscope is rotated ipsilaterally and angulated either cephalically or caudally to maximally visualize the targeted neuroforamen (Fig. 68-7). After aseptic skin preparation and draping, the skin entry site is anesthetized with 1% lidocaine. A 22- or 25-gauge, 3.5-in. spinal needle is then inserted at the injection site and directed down and parallel to the fluoroscopy beam until the needle contacts the superior articular process forming the posterior wall of the neuroforamen. At this point, the needle tip is withdrawn and directed slightly anteriorly to “walk off ” the superior articular process and slip into the neuroforamen. The C-arm is turned to the AP view to assess the needle depth. The needle should be advanced in millimeter-by-millimeter increments in the AP view to ensure that the needle is not advanced past the center of the lateral mass (Fig. 68-8). Overzealous advancement of the needle into the inner half of the lateral mass can potentially lead to penetration of the dura into the subarachnoid space or into the spinal cord. The desired final needle location is the posterior wall of the targeted neuroforamen in the oblique view and the lateral half of the lateral mass in the AP view. After negative aspiration of the cerebrospinal fluid (CSF) or blood, 0.5 to 1 mL of contrast is injected under real-time imaging to exclude a vascular pattern. The needle should be repositioned if there is either blood flashback in the needle hub or a vascular pattern upon contrast injection. If the patient complains of paresthesias or radicular pain, the needle also needs to be repositioned. With satisfactory needle position, the injected nonionic water soluble contrast often outlines the exiting spinal nerve and fills the neuroforamen with epidural spreading or an epidurogram. After the satisfactory position, 1.0 mL of a test dose of 1% lidocaine is injected, and the patient is monitored for 2 minutes for any changes in vital signs or consciousness or neurological deficits in the extremities that would indicate an intravascular injection. For patients without abnormal signs, 40 mg of methylprednisolone, 6 mg of betamethasone sodium phosphate, or 10.25 mg of nonparticulate dexamethasone in a total volume of less than 2 mL per neuroforamen may then be injected (25,26,35). To prevent inadvertent arterial embolism into the spinal cord and brain stem, a nonparticulate soluble corticosteroid such as dexamethasone is recommended for cervical transforaminal ESI.
FIGURE 68-7. Oblique view of transforaminal cervical epidural injections showing needles in the posterior walls of the C4/5 and C5/6 neuroforamina.