Anatomy

There are seven cervical vertebrae but eight cervical nerve roots. The first cervical nerve root is located between the occiput and the atlas, and each subsequent nerve root is located above its corresponding vertebra. If symptoms correlate with the seventh cervical nerve root, the C6-C7 foramen is the target for the block. The cervical neural foramen is a bony canal 4 to 5 mm long through which the cervical nerve roots pass anterolaterally (at about a 45-degree angle with respect to the coronal plane) and downward (at about a 10-degree angle with respect to the axial plane) (Figs. 6-1 to 6-4). Cervical spinal nerves from C3 to C7 exit the intervertebral foramen in the direction of the posterior, lower half of the foramen (Figs. 6-2 to 6-4). The cervical nerve roots occupy about one quarter to one third of the volume of the foramen and is accompanied by radicular arteries and veins (Figs. 6-1 and 6-2).

Figure 6–1 Axial view at the C6 vertebral level. These spinal segmental arteries that arise from the ascending cervical artery and the arterial branches that arise variably from the vertebral artery can be punctured during TFEB. Injection of particulate steroid directly into one of these vessels during procedure can lead to catastrophic paraplegia. Needle tip position should be confirmed by contrast dye injection.

Figure 6–2 Anatomic section through mid-C4 to C7 vertebrae perpendicular to the spinal nerves. Note the intimate relationship of the dorsal nerve roots (DR) with the superior facet and the ventral nerve roots (VR) with the uncinate process and the bottom of the foramen. The upper portion of the foramen is filled with fat tissue (F). Degenerative changes are prominent at the C4-C5 level, where disk material protrudes into the upper portion of the foramen.

(Adapted from Pech P, Daniels DL, Williams AL, et al: The cervical neural foramina: Correlation of microtomy and CT anatomy. Radiology 1985;55:143-146.)

Figure 6–3 Anatomic section through lower end of the C5-C6 neural foramen (left) and corresponding CT scan (right). The spinal nerve exits the foramen anterolaterally (at about a 45-degree angle with respect to the coronal plane) and downward (at about a 10-degree angle with respect to the axial plane). Note the location of the vertebral artery (VA) in relation to the uncinate process and ganglia. DR, dorsal root; F, fat tissue; G, dorsal root ganglion; VR, ventral root.

(Adapted from Pech P, Daniels DL, Williams AL, et al: The cervical neural foramina: Correlation of microtomy and CT anatomy. Radiology 1985;55:143-146.)

Figure 6–4 The anatomic relation between the nerve roots and the discs in the intervertebral foramina. A, C5 nerve root and dorsal root ganglion (DRG); B, C6 nerve root and DRG; C, C7 nerve root and DRG; D, C8 nerve root and DRG. Red dot indicates the center of the DRG. The nerve root sleeve take-off angulation gradually decreases from C5 to C8.

(Modified from Tanaka N, Fujimoto Y, An HS, et al: The anatomic relation among the nerve roots, intervertebral foramina, and intervertebral discs of the cervical spine. Spine 2000;25:286-291.)

The vertebral artery at the caudal portion of the foramen is immediately anterior and medial to the ganglion (Figs. 6-1 to 6-4). In practice, the target points (red dots on Fig. 6-4) should lie directly over the dorsal part of the neural foramen so as to avoid vertebral artery injury.

Procedure

Transforaminal epidural block

1. The patient’s written informed consent is obtained.

2. The patient is placed in the supine position on a table with head slightly extended. It is helpful to place a bolster beneath the shoulder. The overlying skin is prepared and draped in a sterile fashion.

3. The fluoroscopic beam is aligned perpendicular with the vertebral end plates in an AP projection. Then the fluoroscope is rotated obliquely to the ipsilateral side by approximately 45 to 55 degrees to supply the best view of the selected neural foramen (Fig. 6-5). The skin entry point (red open circle on Fig. 6-5) is identified and marked. The local anesthetic is administered at the skin entry site.

4. A 22- or 25-gauge, 1.5-inch needle (or 3.5-inch spinal needle) is advanced to the target point (red circle on Fig. 6-5) by means of a tunnel vision technique. The target point is located posteriorly in the foramen, at the division between the caudal and middle thirds. Use of a short needle, when possible, provides better control.

5. The needle is advanced to the superior articular process by means of a tunnel vision technique. Then the needle is advanced into the neural foramen, touching its posterior border to the halfway point between the medial and lateral borders of the articular pillars in an AP projection. The needle should not be advanced beyond this point, so as to avoid inadvertent injury to the vertebral artery and nerve root (Figs. 6-1 and 6-5). Frequently checking the needle depth during the procedure is crucial in order to avoid procedure-associated complications.

6. 0.5 mL of contrast dye is injected under real-time fluoroscopic guidance through a firmly fixed needle to confirm needle placement and the absence of vascular flow of contrast agent. (Fig. 6-6).

7. A maximum of 2 mL of mixed solution of local anesthetic (0.2%-0.375% ropivacaine or 0.125%-0.25% bupivacaine) and 20 to 40 mg of triamcinolone can be injected.

Figure 6–5 Target points for cervical TFEB and SNRB on an oblique radiograph of the cervical spine. Red circles indicate the target points. A curved block needle should be advanced to the target point with use of the tunnel vision technique. The target point is posteriorly in the foramen, at the division between the caudal and middle third.

Figure 6–6 The procedure of cervical TFEB at the level of C6-C7. A, The needle is advanced to the superior articular process, at the division between the caudal and middle thirds. B, Contrast dye spreads along the C7 nerve. C, The AP image shows that contrast dye has spread along the nerve root as well as the epidural space. The needle is advanced into the neural foramen to the halfway point between the articular pillars. To avoid inadvertent injury to the vertebral artery and nerve root, the needle should not be advanced more deeply.

Selective nerve root block

SNRB is performed by means of the same technique as for TFEB, except for the final position of the needle tip. The needle is advanced until the patient experiences paresthesia or until the needle tip is located just medial to the lateral articular process at the desired level. At this point, less than 0.5 mL of contrast dye is injected under real-time fluoroscopic guidance through a firmly fixed needle to confirm needle placement. The contrast dye will flow in a linear fashion and surround the nerve root, forming a tubular defect (Fig. 6-7).

Figure 6–7 AP fluoroscopic image showing spread of contrast dye along the nerve root.

For diagnostic specificity, the injectate should not go into the epidural space.

Careful assessment of the vascular flow of contrast dye is necessary to avoid a false-negative result.

If there is venous filling, the needle can be slightly withdrawn or advanced until the needle tip is in the extravascular space. Subsequently, when the optimal needle position is confirmed, less than 0.5 mL of local anesthetic is administered, under fluoroscopic guidance to allow observation of the contrast dye dilution.

The medication is instilled slowly to minimize the retrograde flow of injectate into the epidural space.

Anatomy

Thoracic spinal nerves exit the intervertebral foramen in the direction of the posterior, upper half of the foramen [25]. The anatomy of the upper thoracic levels (T1-T8)—the shape of the lamina, the narrow spaces between ribs, and the wide bases of the transverse processes—makes it difficult to reach the intervertebral foramen. Accurate positioning of the straight cannula for the TFEB or SNRB procedure is consequently also difficult. Use of a curved needle makes it easy to position the cannula accurately.

Understanding the anatomy of the artery of Adamkiewicz is crucial to the procedure of TFEB or SNRB (Fig. 6-8) [26]. This artery is the largest of the radicular arteries supplying the lower two thirds of the spinal cord. It is mostly found from T9 to L1 (approximately 80% of cases). Injury to the artery of Adamkiewicz can result in devastating ischemia of the lower spinal cord, causing anterior spinal artery syndrome. Care should be taken in performance of these interventional pain procedures at the neural foramina from T9 to L1.

Figure 6–8 Arteries of the spinal cord. The artery of Adamkiewicz arises from the aorta and enters the spinal cord.

Procedure

Thoracic TFEB or SNRB should be performed with particular care and under fluoroscopic guidance to avoid penetration of the pleura.

Transforaminal epidural block

1. The patient’s written informed consent is obtained.

2. The patient is placed in the prone position. The overlying skin is prepared and draped in a sterile fashion.

3. The fluoroscopic beam is aligned perpendicular with the vertebral end plates in an AP projection and then is rotated to a 10- to 20-degree oblique angle toward the side being injected. The skin entry point is identified and marked (Figs. 6-9 and 6-10A). The local anesthetic is administered at the skin entry site.

4. A 22- or 25-gauge, 3.5-inch, curved spinal needle is then advanced to the posterior surface of the vertebral body at the suspected symptomatic radicular level(s) in same direction of needle with fluoroscopic beam (Fig. 6-10B). And the needle depth is frequently checked on a lateral projection. Frequent checking is crucial to ensure that the needle tip does not enter the pleura (Fig. 6-10C).

5. The needle is directed to the inferior portion of the proximal rib, and contrast dye is used to visualize the nerve root. Contrast dye should be injected under real-time fluoroscopic guidance through a firmly fixed needle to confirm needle placement and the absence of vascular flow of the contrast dye (Fig. 6-10D). Vascular injection of steroids can result in devastating paraplegia, especially at the levels T9 to L1, the most common location of the artery of Adamkiewicz.

6. A maximum of 2 mL of local anesthetic (0.2%-0.375% ropivacaine or 0.125%-0.25% bupivacaine) and 20 to 40 mg of triamcinolone can be injected.

Figure 6–9 Skin entry point (red dots) for thoracic TFEB. A red dotted line represents mediastinal line. P, pedicle; R, rib.

Figure 6–10 Thoracic TFEB. A, Oblique spot fluoroscopic image of the thoracic spine with a clamp over the target point, just inferior and lateral to the pedicle. B, The needle is advanced toward the target point with use of a curved needle technique under fluoroscopic guidance. The physician should be vigilant to avoid injuring the pleura during the procedure. C, The needle is advanced to the posterior vertebral body in the lateral image. D, The AP image shows spread of contrast dye along the nerve root as well as in the epidural space.

Anatomy

The lumbar nerve travels inferiorly and exits in a lateral plane, under the pedicle, with a downward course at varying angles from the horizontal according to the vertebral level, thus occupying the superior portion of each foramen (Fig. 6-15). A “safe triangle” has been defined for this procedure. It is the area between the horizontal base of the pedicle, the lateral border of vertebral body, and the connecting diagonal nerve root (Fig. 6-11) [27].

Figure 6–15 Target points for SNRB. Red dots indicate the target points for L1 to L5.

Figure 6–11 The “safe triangle” is composed of an upper side made up by the base of the pedicle, a tangential side that corresponds to the exiting nerve root, and a third side defined by the lateral border of the vertebral body.

Procedure

Transforaminal epidural block

1. The patient’s informed consent is obtained.

2. The patient is placed in the prone position on a radiology table. The overlying skin is prepared and draped in a sterile fashion.

3. The fluoroscope is rotated in the caudocephalad direction to align parallel with the end plates in an AP projection. Then the fluoroscope is rotated to a 20- to 30-degree oblique angle, toward the side being injected, to bring the “Scotty dog” appearance of the spine into view (Fig. 6-12). The skin entry point is identified and marked (red dot on Figs. 6-13 and 6-14A). The local anesthetic is administered at the skin entry site.

4. A 22- or 25-gauge, 3.5-inch, curved spinal needle is advanced to the posterior surface of the vertebral body at the suspected symptomatic radicular level (Fig. 6-14B) by means of a tunnel vision technique under fluoroscopic guidance.

5. AP and lateral fluoroscopic images are used to confirm needle placement. To reduce the risk of dural puncture, the needle should not be placed medially while being passed through mid-pedicle in the oblique view.

6. 0.5 to 1 mL of contrast dye is injected to confirm the epidural flow of the injectate and to rule out intravascular, intrathecal, or soft tissue infiltration (Figs. 6-14C and 6-14D).

7. A mixed solution of 2 to 3 mL of local anesthetic (0.2%-0.375% ropivacaine or 0.125%-0.25% bupivacaine) and 20 to 40 mg of triamcinolone can be injected.

Figure 6–12 For lumbar SNRB, the C-arm is rotated to a 20- to 30-degree oblique angle toward the side being injected, a movement that brings the facet joint and “Scotty dog” appearance into view. IAP, inferior articular process; P, pedicle; SAP, superior articular process; TP, transverse process.

Figure 6–13 Target point for TFEB. The red dot indicates the target point, which lies at the “6 o’clock” position if the pedicle is regarded as a clock face.

Figure 6–14 The needle is positioned at the safe triangle in the oblique image (A) and just beneath the pedicle (B) and is advanced to the posterior vertebral body in the lateral image (C). C and D, Spreading of contrast agent demonstrates the epidural flow in the ventral epidural space medial to the pedicle.

Selective nerve root block

SNRB is performed by means of the same technique as TFEB, except for the final position of the needle tip.

The target points for L1 to L5 SNRB are located more laterally than those for TFEB, to avoid epidural spread of the injectate. The target points for L1 to L5 SNRB also differ according to the vertebral level involved (Fig. 6-15).

When the needle is close to the nerve root, the needle is advanced slowly until it is adequately placed at the target or until the patient experiences paresthesia. Provocation of paresthesia is not mandatory for an SNRB. SNRB using a nerve stimulator guarantees a safe and precise block.

When the patient experiences paresthesia, 0.5 mL of contrast dye is injected under fluoroscopic guidance using an AP image. This injection confirms that the needle tip is appropriately placed near the nerve root and ensures that the injectate is not passing epidurally or intravascularly (Fig. 6-16).

Figure 6–16 An AP fluoroscopic image of right L5 SNRB. Spreading of contrast agent demonstrates the right L5 nerve root. No intravascular, intrathecal, or epidural spread of contrast is noted.

After proper localization of the needle tip is confirmed, 0.5 mL of local anesthetic is injected through the needle.