Chapter 6 Transforaminal Epidural Block and Selective Nerve Root Block
Transforaminal epidural block (TFEB) is defined as spread of an injectate through the epidural space as well as along the spinal nerve. It is used therapeutically because the injectate spreads into the anterior epidural space, which is the perceived target site of the disease. Local anesthetics with or without steroid can be used. TFEB injections can control inflammation and can stabilize sensitized nociceptive neural activity due to the many different pain sources originating in the spine.
TFEB requires a lower volume (1-3 mL) of injectate than conventional epidural block achieved by direct injection to the anterior epidural space. This smaller volume can decrease the toxicity from the injectate. No further injection is recommended if the first TFEB was not effective. If the initial response to TFEB is favorable but short-lived, a series of injections (3-6 times per year) or pulsed radiofrequency lesioning of the corresponding dorsal root ganglion (DRG) is recommended (see Chapter 7). The interval for sequential block varies from days to weeks for a series of injections.
Real-time fluoroscopic guidance during the injection of contrast material is essential. Provocation of paresthesia is not mandatory for SNRB. SNRB under fluoroscopic guidance or with use of a nerve stimulator guarantees a safe and precise block. Frequent checks of anteroposterior (AP) and lateral images with the fluoroscope are highly recommended to avoid direct trauma to spinal nerves.
Treatment objectives
Transforaminal Epidural Block
The treatment objectives of TFEB are to relieve pain and to increase the quality of life by:
Indications
Transforaminal Epidural Block
Indications for TFEB are as follows [1–10]:
Radicular pain when urgent surgery either is not indicated or is contraindicated by medical conditions
Contraindications
Contraindications to both TFEB and SNRB are as follows [11,16]:
Therapeutic anticoagulation (aspirin and antiplatelet agent therapy should be stopped 7 days, and warfarin therapy 5 days, before TFEB or SNRB)
Preoperative preparation
History
The history for a patient who is to undergo TFEB or SNRB should include questions about pain characteristics, such as the quality and location of the pain, onset, and any relieving and aggravating factors. Questions should also be asked to identify “red flags”—signs and symptoms that might indicate the presence of cancer, cauda equina syndrome, or infection (Table 6.1).
Table 6.1 “Red Flags” in a Patient to Undergo Spinal Nerve Block: Signs and Symptoms Needing Rapid Evaluation and Operation
| Cancer-related signs | |
| Cauda equina syndrome-related signs | |
| Infection-related signs |
Anesthesia
Typically, very little or no sedation is required for a TFEB or SNRB. Local skin infiltration, if needed, can be performed with 1% to 2% lidocaine. For very anxious patients, conscious sedation can be achieved with a combination of fentanyl, ketorolac, and midazolam.
Anatomy and procedures
Cervical Region
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.
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