Selective Nerve Blocks

Selective lumbar nerve root injections are performed by using the technique described for transforaminal epidural injections. The undersur-face of the pedicle is profiled from a posterior oblique angle (Figure 9.3). For a selective nerve root block, however, the goal is to avoid re-fluxing the therapeutic injectate into the epidural space. Rather, minimal epidural reflux is achieved by directing the needle slightly lateral to the 6 o'clock position relative to the pedicle. In this fashion, a limited amount of the mixture of contrast and therapeutic agents is injected to achieve primarily nerve sheath infiltration with minimal epidural reflux (Figure 9.9). Typically, 0.5 to 1.5 mL of nonionic iodi-nated contrast are injected (use only contrast agents that are approved for myelographic use).

Figure 9.6. Posterior oblique approach or intralaminar cervical epidural injection. After contact with the lamina for depth control, the needle is guided over the superior margin of the lamina into the dorsal epidural space.

Intralaminar Space

After needle positioning and negative aspiration, the contrast agent is injected. The films are obtained in the AP and oblique projections to document distribution of contrast media prior to the installation of local anesthetic and water-soluble steroid suspension. Usually, less than 2 mL of the therapeutic mixture is injected to avoid significant epidural reflux. If there is significant epidural reflux, selectivity is lost, and a positive response cannot reliably be attributed to blockade of the intended nerve. Therefore, if contrast injection reveals significant epidural reflux, the needle should be repositioned more laterally and additional contrast injected prior to filming and the injection of therapeutic substances.

An S1 nerve block is performed by using the technique described for a transforaminal S1 injection (Figure 9.5). A limited amount of the mixture of contrast and therapeutic agents is injected, however, to avoid significant epidural reflux. Typically, volumes less than 1.5 mL will not cause significant reflux into the epidural space.

Cervical nerve blocks should be performed only by proceduralists who have significant experience performing other spinal injection procedures. Precise needle positioning is critical because there are structures immediately adjacent to the nerve sheath that must be avoided.

Vertebral Needle

Figure 9.7. (A) Oblique radiograph after needle tip is directed to the lamina. (B) AP radiograph demonstrating needle contact with the lamina.

Vertebral Needle

Figure 9.7. Continued. (C) Right posterior oblique (contralateral to left paramedian approach) radiograph after needle had been directed over the lamina into the dorsal epidural space. Contrast gently directed to firm needle placement within the epidural space.

Figure 9.7. Continued. (C) Right posterior oblique (contralateral to left paramedian approach) radiograph after needle had been directed over the lamina into the dorsal epidural space. Contrast gently directed to firm needle placement within the epidural space.

Paramedian Approach Epidurals

At the infralateral aspect of the neural foramen, the cervical nerve sheath can be safely injected. However, just medial to this, the vertebral artery traverses the spinal column. If a lateral approach to the foramen is utilized, it is not difficult to place the needle within the spinal canal, which may result in spinal cord damage. Thus we use an an-terolateral approach, which does not allow direct access to the spinal canal through the foramen. As in the lumbar spine, bony landmarks are used as a visual aid and for tactile response provided by needle placement on the bone for depth control and anchoring prior to injection of contrast and therapeutic materials. If the vertebral artery is inadvertently encountered, the injection of a small amount of contrast will reveal the untoward placement. It is important to recognize this, since a subintimal injection could result in vertebral artery occlusion. Even worse, intra-arterial injection of the therapeutic mixture could result in seizures, stroke, or even death. Therefore, a radiculogram is essential for assuring accurate needle placement prior to the injection of therapeutic substances (Figure 9.10). Typically, less than 1 mL of contrast is necessary to confirm needle positioning and opacify the nerve sheath. After filming and confirmation of the needle position, 1 to 5 mL of a therapeutic mixture is injected. Patients are monitored for 20 to 30 minutes after the injection for initial response. The response is rated for therapeutic efficacy by asking the patient to provide a percentage improvement from 0 ("RO") to 100% ("R2"). Partial improvement (1-99%) is designated "R1."

Thoracic Epidural TechniqueCervical Epidural Contrast Pattern

Figure 9.8. Radiographs following injection of contrast medium demonstrate opacification of cervical and upper thoracic epidural compartment bilaterally: (A) oblique and (B) AP views.

Figure 9.8. Radiographs following injection of contrast medium demonstrate opacification of cervical and upper thoracic epidural compartment bilaterally: (A) oblique and (B) AP views.

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