Preganglionic approach to transforaminal epidural steroid injections.

Abstract

Several studies have demonstrated the efficacy of transforaminal epidural steroid injections (TFESI) for the treatment of lumbosacral radicular pain. 1–4 Using standard TFESI technique, the spinal needle is positioned within the “safe triangle” (bordering the pedicle, the exiting nerve root, and the posterolateral border of the vertebral body), with the bevel below the inferior aspect of the pedicle. In a selective nerve root block, the injectate typically bathes the epidural space around the dorsal root ganglion and descends along the distal aspect of the nerve root (Fig. 1, bottom arrow). Ideally, if there is no stenosis, and the needle tip is appropriately positioned, the injectate may spread rostrally to the epidural portion of the preganglionic nerve root as well (Fig. 1, top arrow).Figure 1:: Fluoroscopic image (anteroposterior view) of transforaminal selective nerve root and epidural steroid injection of the left L4 nerve root. Bottom arrow, distal aspect of the nerve root; top arrow, epidural portion of the preganglionic nerve root.In most cases of lumbosacral radiculopathy secondary to stenosis or a herniated disc, the site of impingement usually lies at the level of the supra-adjacent intervertebral disc, which is rostral to the conventional lumbar TFESI bevel position. However, one cannot always guarantee a rostral spread of injectate to bathe the epidural/preganglionic portion of the nerve root. As an example, in treating a right S1 radiculopathy with TFESI at the exiting nerve root location (S1 foramen), the injectate failed to ascend to the L5-S1 disc level (Fig. 2, bottom arrow). In situations like this, one may wish to consider a supplementary preganglionic TFESI approach. The fluoroscopic landmarks utilized for needle positioning are similar to those used for intradiscal procedures (lateral to the superior articular process and parallel to the superior endplate of the vertebral body). The final needle position is at the inferior aspect of the supra-adjacent neural foramen, with the bevel immediately dorsal to the annulus/posterior longitudinal ligament. Injection at this position places the aliquot at the epidural preganglionic site of neural impingement, where the traversing nerve root is in closest proximity to the disc. The injectate may also descend to the intraforaminal and epidural portion of the exiting nerve root (Fig. 2, top arrow).Figure 2:: Fluoroscopic image (anteroposterior view) of epidural steroid injection of the right S1 root. Bottom arrow, L5-S1 disc level; top arrow, intraforaminal and epidural portion of the exiting nerve root.Theoretical advantages of the preganglionic TFESI technique include placing of the injectate closer to the site of neural impingement and providing a more effective washout of inflammatory disc material. Perhaps this methodology may be useful as a supplementary injection technique to the conventional TFESI, especially in patients who demonstrate poor rostral spread of injectate toward the epidural/preganglionic portion of the nerve root. A prospective, randomized, controlled trial may be needed to verify its clinical efficacy and further define its utility.