Transforaminal Epidural Block and Selective Nerve Root Block

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Chapter 6 Transforaminal Epidural Block and Selective Nerve Root Block

Sang-Sik Choi, MD, Yong-Chul Kim, MD, PhD

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.

Selective nerve root block (SNRB) is defined as spread of injectate not into the epidural space but along the spinal nerve. It is used for diagnostic purposes. SNRB can be used to define the source of pain and is especially useful when clinical findings and results of electrodiagnostic and imaging studies are equivocal. In addition, SNRB may be particularly useful in identifying the symptomatic level in patients with multilevel pathology.

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:

image Providing a speedy return to physical functioning and work
image Restoring the ability to perform activities of daily living
image Allowing participation in recreation activities

Selective Nerve Root Block

The treatment objectives of SNRB are to identify nerve roots responsible for pain when clinical or radiographic studies are equivocal and to plan for surgical treatment.

Indications

Transforaminal Epidural Block

Indications for TFEB are as follows [1–10]:

image Nonsurgical treatment of atraumatic spondylotic or traumatic spondylotic radicular pain
image Radicular pain of postoperative scarring
image Radicular pain when a surgically correctable lesion cannot be found
image Radicular pain when urgent surgery either is not indicated or is contraindicated by medical conditions
image Postherpetic neuralgia
image Spinal stenosis—especially in symptomatic foraminal stenosis
image Sometimes for discogenic pain
image Postoperative back pain when anatomical considerations make a translaminar approach unfeasible

Selective Nerve Root Block

Indications for SNRB are as follows [11–15]:

image To identify nerve root(s) responsible for pain when clinical or radiographic findings are equivocal
image For diagnosis of atypical extremity pain
image To confirm anomalous innervations, such as conjoined nerve roots or furcated nerves
image To confirm the pain generator in failed back surgery syndrome with atypical extremity pain
image To confirm the pain generator in patients with transitional vertebrae
image For planning of surgical treatment

Contraindications

Contraindications to both TFEB and SNRB are as follows [11,16]:

image Patient refusal
image Coagulopathy
image Allergy to injectates
image Therapeutic anticoagulation (aspirin and antiplatelet agent therapy should be stopped 7 days, and warfarin therapy 5 days, before TFEB or SNRB)
image Skin infection at the injection site
image Raised intracranial pressure
image Uncorrected severe hypovolemia
image Pregnancy
image Motor deficit
image Medullar cone symptoms

Complications

Complications of TFEB or SNRB are as follows [17–24]:

image Infection: epidural abscess, meningitis
image Bleeding: epidural hematoma
image Allergic reaction to injectates
image Dural puncture (0.5%-2.5% of cases), dural puncture headache
image Intravascular injection
image Postinjection exacerbation of pain (1% of cases)
image Arachnoiditis with certain preparations of steroids
image Suppression of plasma cortisol levels for up to 2 weeks
image Increase in blood glucose level from steroid injection
image Vasovagal reactions and ataxia, especially for cervical block
image Neurologic complications due to direct nerve trauma
image Paraplegia

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
Prior history of cancer
Unexplained rapid weight loss
The progression of pain in spite of usual therapy to improve pain
Resting pain or worsening pain with supine position
Night pain

Cauda equina syndrome-related signs
Trauma-related onset
Bowel/bladder incontinence or retention
Saddle anesthesia
Bilateral sciatica or numbness
Bilateral lower extremity motor weakness
Progressive neurologic deficit

Infection-related signs
Persistent fever or chilling
Recent urinary tract infection or other bacterial infection
Previous surgery
History of intravenous drug abuse
Immunocompromised state (e.g., systemic corticosteroid use, organ transplantation, human immunodeficiency virus)

Physical and Neurologic Examinations

The physical and neurologic examinations of a patient who is to undergo TFEB or SNRB should identify factors such as:

image Segmental pain to the particular spinal segmental area
image Intermittent neurologic claudication
image Motor weakness

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.

Instruments

The following instruments are required:

image Skin infiltration needle, 25-gauge, 1.5-inch
image Spinal needle, 22- or 25-gauge, 3.5-inch
image If possible, 3.5-inch SMK needle electrode for evoking paresthesia during the procedure
image Injection syringes, 2 mL
image Extension tube for injection of contrast material
image Solutions: local anesthetic (e.g., lidocaine, bupivacaine, ropivacaine) and/or steroid (e.g., triamcinolone)

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).

image

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.

image

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.)

image

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.)

image

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

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