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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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PLACEMENT

Cervical Transforaminal Injection

Anatomy.

At typical cervical levels, the ventral and dorsal roots of the spinal nerves descend in the vertebral canal to form the spinal nerve in their intervertebral foramen. The foramen is oriented obliquely anteriorly and laterally. Its roof and floor are formed by the pedicles of consecutive vertebrae. Its posterolateral wall is formed largely by the superior articular process of the lower vertebra and in part by the inferior articular process of the upper vertebra and the capsule of the zygapophysial joint formed between the two articular processes. The anteromedial wall is formed by the caudad portion of the upper vertebral body, the uncinate process of the lower vertebra, and the posterolateral corner of the intervertebral disc. Immediately lateral to the external opening of the foramen, the vertebral artery rises closely anterior to the articular pillars of the zygapophysial joint.

The spinal nerve, in its dural sleeve, lies in the caudad half of the foramen. The cephalad half is occupied by epiradicular veins. The ventral ramus of the spinal nerve arises just lateral to the intervertebral foramen and passes anteriorly and laterally onto the transverse process. Radicular arteries arise from the vertebral artery and the ascending cervical artery and accompany the spinal nerve and its roots to the spinal cord.

Position.

The procedure can be performed with the patient lying in a supine, oblique, or lateral decubitus position, depending on operator’s preference and the patient’s comfort. The position must allow adequate visualization of the cervical intervertebral foramina in the anteroposterior (AP), lateral, and oblique planes ( Fig. 44-1 A ).

Click to view full size figure

Figure 44-1  Cervical transforaminal and selective nerve root injection. A, Proper patient positioning and C-arm angulation. B, Needle placement along the axis of the intervertebral foramen under fluoroscopic guidance. C, Axial view of the needle position demonstrating the angle of the foramen and adjacent structures. D, Final needle position for transforaminal injection within the intervertebral foramen and selective nerve root injection just lateral to the foramen. E, Right anterior oblique radiograph demonstrating a needle in position along the posterior aspect of the right C6-C7 intervertebral foramen. Inset of midportion of image with bony structures labeled: C6, C6 vertebral body; C7, C7 vertebral body; Ped, pedicle; La, lamina; SpP, spinous process; SAP, superior articular process; IAP, inferior articular process. F, Final anteroposterior radiograph following cervical transforaminal injection with the needle in its final position and radiographic contrast outlining the exiting nerve root (arrowheads) and extending into the lateral epidural space (arrows).


The important first step is to obtain a correct oblique view of the target foramen ( Fig. 44-1 B ). In this view the foramen is maximally wide transversely, and the anterior wall of the superior articular process projects onto the silhouette of the lamina. If these criteria are not satisfied, the inclination of the fluoroscope must be adjusted until they are. The correct oblique view is essential because in less oblique views, which may nevertheless show a foramen, the vertebral artery lies along the course of the needle.

Needle Puncture.

A 25-gauge, 2.5- to 3.5-inch needle is passed into the neck through a skin puncture at a point overlying the posterior half of the target foramen. Its tip should always lie over the anterior half of the superior articular process lest it be inserted prematurely and too far into the foramen. Once the needle has reached the superior articular process, its depth is noted. Subsequent insertion should not be more than a few millimeters beyond this depth. The needle is then deliberately repositioned to enter the foramen tangential to its posterior wall, opposite the equator of the foramen ( Fig. 44-1 C –E). Cephalad to this level, the needle may encounter veins; caudad to this level, the needle may encounter the spinal nerve and its arteries. The needle must stay in contact with the posterior wall lest it encounter the vertebral artery.

Under an AP fluoroscopic view, the tip of the needle is finally adjusted so it lies opposite the parasagittal midline of the articular pillars. Insertion beyond this depth increases the likelihood of puncturing the dural sleeve or thecal sac. The final needle position is checked and radiographically recorded on an oblique view (which documents needle placement against the posterior wall of the foramen) and on an AP view ( Fig. 44-1 F ) (which documents the depth of needle insertion).

Under direct, real-time fluoroscopy, a small volume of non-ionic contrast medium (1.0 mL or less) is injected. The solution should outline the proximal end of the exiting nerve root and spread centrally toward the epidural space (see Fig. 44-1 F ).

Once the target nerve has been correctly outlined, a small volume of a short-acting local anesthetic (1% lidocaine 0.5–1.5 mL) is injected to block the target nerve and to render the subsequent injection of corticosteroid less painful. While ensuring that the needle has not displaced, the procedure is completed by injecting a small dose of corticosteroid (3.0–6.0 mg betamethasone or 20–40 mg triamcinolone).

Potential Problems.

Real-time fluoroscopy is essential to verify there is no unintentional intra-arterial injection, which may occur even if the needle is correctly placed. Intra-arterial injection manifests by extremely rapid clearance of the injected contrast material. In a vertebral artery, the contrast material streaks cephalad. In a radicular artery, it blushes briefly in a transverse fashion medially toward the spinal cord. In either instance, the needle is withdrawn and no further injections are attempted. The procedure is then rescheduled after a period long enough for the puncture wound to have healed.

Sometimes the contrast medium fills epiradicular veins. This situation is recognized by slow clearance of the contrast medium, which is characteristic of venous flow. In that event, the needle is adjusted either by slightly withdrawing it or redirecting it to a position slightly more caudad on the posterior wall of the foramen.

Only a small volume of contrast medium (1.0 mL or less) is required to outline the dural sleeve of the spinal nerve. As it spreads onto the thecal sac, the contrast medium assumes a linear configuration. Rapid dilution of the contrast medium implies subarachnoid spread, which may occur if the needle punctures the thecal sac when there is lateral dilation of the dural root sleeve into the intervertebral foramen. In that event, the procedure is abandoned and rescheduled lest subsequently injected material penetrate the puncture made through the dura.

Lumbar Transforaminal Injection

Anatomy.

At lumbar levels, the ventral and dorsal roots of the spinal nerves descend in the vertebral canal to form the spinal nerve in their respective intervertebral foramen. The foramina are oriented laterally. The foraminal roof and floor are formed by the pedicles of consecutive vertebrae. The posterolateral wall is formed largely by the superior articular process of the lower vertebra and in part by the inferior articular process of the upper vertebra and the capsule of the zygapophysial joint formed between the two articular processes. The anteromedial wall is formed by the caudad end of the upper vertebral body and the posterolateral corner of the intervertebral disc.

The spinal nerve, in its dural sleeve, exits obliquely through the foramen. In the cephalad half of the foramen, the dorsal root ganglion lies just deep to the pedicle of the cephalad vertebra; this region is also occupied by epiradicular veins. As the root traverses inferolaterally through the foramen, it divides into a ventral and dorsal ramus. The ventral ramus of the spinal nerve passes anteriorly and laterally adjacent to the transverse process of the caudad vertebra bounding the foramen. Radicular arteries arise from the abdominal aorta and its branches and accompany the spinal nerve and its roots to the spinal cord. As in the cervical region, the location and size of the radicular arteries are variable, and recognizing their presence and their importance to carrying out this block effectively must be emphasized.

Position.

The procedure is typically performed with the patient in the prone position, with a pillow under the abdomen above the iliac crests and the pelvis tilted anteriorly ( Fig. 44-2 A ). The first step is to obtain a 10- to 20-degree oblique view of the target foramen that allows the needle to pass into the lateral aspect of the intervertebral foramen. This is most difficult for the L5–S1 level, where the iliac crest blocks entry to the foramen when the oblique angle is too extreme.

Click to view full size figure

Figure 44-2  Lumbar transforaminal and selective nerve root injection. A, Proper patient positioning and C-arm angulation. B, Needle placement under fluoroscopic guidance. C, Axial view of the final needle position for transforaminal and selective nerve root injection. D, Lateral view of the final needle position for transforaminal and selective nerve root injection. E, Final anteroposterior radiograph after contrast injection following selective nerve root injection (left L5) with the needle tip along the superior surface of the nerve root (arrow) and contrast outlining the nerve root and extending into the lateral epidural space (arrowheads).


Needle Puncture.

Through a skin puncture point overlying the superior portion of the target foramen, just caudad to the pars interarticularis (the junction of the transverse process with the lamina or just caudad to the proximal-most portion of the transverse process), a 25-gauge, 2.5- to 3.5-inch needle is passed into the back ( Fig. 44-2 B ). Its tip should always lie over the posterior aspect of the intervertebral foramen ( Fig. 44-2 C ). Once the needle has reached the pars interarticularis, its depth should be noted; and the radiographic image orientation is switched to the lateral projection ( Fig. 44-2 D ). Subsequent insertion is carried out using the lateral projection, observing the needle as it enters the foramen. The needle is advanced slowly; further insertion is halted if the patient reports a paresthesia or the needle reaches the midportion of the foramen in the AP dimension.

The final needle position is checked and recorded on an AP view, which documents the medial extent of the needle’s advancement. Under direct, real-time fluoroscopy in the AP view, a small volume of non-ionic contrast medium (1.0 mL or less) is injected. The solution should outline the proximal end of the exiting nerve root and spread centrally underneath the pedicle toward the epidural space ( Fig. 44-2 E ).

Once the target nerve has been correctly outlined, a small volume of a short-acting local anesthetic (1% lidocaine1 0.5–1.5 mL) is injected to anesthetize the target nerve and to render the subsequent injection of corticosteroid painless. While ensuring that the needle has not displaced, the procedure is completed by injecting a small dose of corticosteroid (betamethasone 3.0–6.0 mg or triamcinolone 20– 40 mg).

Potential Problems.

Similar to cervical transforaminal injection, real-time fluoroscopy is essential to check for unintentional intra-arterial injection, which may occur even if the needle is correctly placed. Intra-arterial injection manifests by extremely rapid clearance of the injected contrast material. In a radicular artery, the contrast blushes briefly in a transverse fashion medially toward the spinal canal. In this instance, the needle is withdrawn and no further injections are attempted. The procedure is then rescheduled after a period long enough for the puncture wound to have healed.

Contrast medium may also fill epiradicular veins, which is recognized as slow clearance of the contrast medium (characteristic of venous flow). In this setting, the needle is adjusted by slightly withdrawing it or redirecting it to a position slightly more caudad within the foramen.

Only a small volume of contrast medium (1.0 mL or less) is required to outline the dural sleeve of the spinal nerve. As it spreads onto the thecal sac the contrast medium assumes a linear configuration (see Fig. 44-2 E ). Rapid dilution of the contrast medium implies subarachnoid spread, which may occur if the needle has punctured the thecal sac when there is lateral dilation of the dural root sleeve into the intervertebral foramen. In that case, the procedure should be abandoned and rescheduled lest subsequently injected material penetrate the puncture made through the dura.

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