1 Imperial College Healthcare NHS Trust, London, UK 2East Kent Hospitals University Foundation NHS Trust, Canterbury, UK
Introduction
Unlike the popularity of lumbar transforaminal epidural blocks, fluoroscopy-guided cervical and thoracic transforaminal blocks are usually practised only by experienced clinicians [1]. This is mainly due to the high risk of complications as a result of vascular injury and potential damage to the thecal sac and spinal cord [2]. However, with the advent of ultrasound-guided procedures which enable the operator to visualize the vascular structures in real time, some safety concerns have been addressed with some practitioners using a combined USG and fluoroscopy-guided approach [3]. This combined ultrasound (US) and X-ray guided cervical transforaminal epidural/nerve root block gives an opportunity to perform this procedure in supine or lateral position. It also negates the possibility of potential injury of soft tissues including nerves and vessels in the needle trajectory while performing the procedure [4].
Figure 25.1 Cervical-lateral view anatomy and fluoroscopy showing vertebral body, articular process, transverse process, spinous process, and facet joints.
Figure 25.2 Cervical-lateral oblique view showing the foramen, anterior, and posterior tubercle.
Figures 25.3 (a–c) Lateral view of cervical vertebra in relation to the soft-tissue structures (a), nerve roots (b) and vertebral artery (c).
C1–C7 levels
All transverse processes of the cervical vertebrae C1 to C7 have foramina transversaria which houses the vertebral artery and the sympathetic plexus from C6 upward [5]
C3–C6 always have anterior and posterior tubercles with a groove for the nerve root inbetween
C1 and C7 have a longer transverse process compared to the rest of the cervical vertebrae
C2 transverse process is rudimentary compared to others
C6 anterior tubercle is the most predominant in most people and is called the “Chassaignac tubercle”
C7 has no anterior tubercle. Hence, the vertebral artery is exposed next to the nerve root
C2–C3 has the largest intervertebral foramina
C7 spinous process is the most prominent spinous process.
Figure 25.4 Sonoanatomy picture of C5, 6, and 7 nerve roots and C7 nerve root relationship to the vertebral artery.
Figure 25.5 Sonoanatomy of C6 nerve root just out of C6 foramen.
Figure 25.6 Sonoanatomy of C6 nerve root post-injection with needle in position.
Nerve root occupies the lower part of the foramen
The epiradicular vein lies on the upper part of the nerve root and the radicular arteries lie in close proximity (within 2 mm proximity of the needle path) [6]
One third of these vessels enter the foramen from the posterior aspect and form radicular or segmental feeding vessels to the spinal cord making it vulnerable to inadvertent injection or injury
Use of US guidance, or in combination with fluoroscopy, has the potential to improve the safety profile to carry out cervical transforaminal epidural needle positioning and nerve root block compared to fluoroscopy alone
Points to remember: There is very little anatomic symmetry between different patients or between each side in an individual patient [5]. This can be better appreciated when US is used.
Figure 25.7 Anatomy and relationship of thoracic vertebra, ribs and nerve roots.
T2–10 are the “standard” thoracic spines
The transverse process lies lateral and posterior to the articular process and articulates with the corresponding ribs. This articulation makes the acoustic window in this region narrower
T11–12 transverse process are rudimentary
Thoracic nerve root blocks are better performed to check needle-tip position under X-ray as US has limitations to see this due to the acoustic shadow of bone. US is superior in identifying the thoracic paravertebral space and avoids lung injury and potential pneumothorax.
As a diagnostic procedure to confirm level prior to discectomy
Acute herpes zoster (shingles)
Postherpetic neuralgia
Cervicalgia
Cervical spondylosis
Post-surgical pain
Cervicogenic headache
CRPS resistant to sympathetic block.
Cervical transforaminal epidural or nerve root block is used for diagnostic purposes as well as therapeutic uses. Compared to interlaminar epidurals, this approach offers the advantage of delivering a concentrated amount of the injected steroids to the localized area of nerve root with a small volume of the injectate where the foraminal compression is maximum [8].
The diagnostic nerve root injections are done to determine the specific cause of pain. This can be done as a selective nerve root block or a specific level transforaminal epidural block.
Types of Nerve Root Block
Selective nerve root block (SNRB): The selective nerve root block is only done using local anesthetic and no steroids are used.
Nerve root block: Diagnostic or therapeutic using local anesthetic +/- steroid.
Inability to have an informed consent or lack of willingness to consent to the procedure.
Caution to be exercised in the following:
Abnormal anatomy of cervical/thoracic spine
Spinal fixators and prosthesis
Pregnancy
Immunosuppression.
Technique
There are multiple approaches for both cervical and thoracic transforaminal epidural blocks [9]. Combining fluoroscopy and US improves patient comfort, safety, reduces complications and maintains the opportunity to perform them without the need for complex facilities such as CT and DSA which pose the risk of increased radiation exposure [10].
Fluoroscopic approach
Ultrasonographic approach
Combined fluoroscopic and US approach
CT-guided approach.
Pre-procedure Preparations
Irrespective of the techniques used, there are some important pre-procedural preparations that are needed to improve patient comfort, decrease the incidence of procedural complications, and reduce potential litigation [11]:
History: A detailed history about pain, medications, allergies, and other medical conditions that could potentially affect the procedure should be noted.
Exam: A clinical and neurologic examination should be performed and documented.
Investigations: As appropriate to the clinical condition, relevant investigations should be performed and reviewed accordingly [12].
Consent: Explain the risks and benefits of the procedure to be done. Common and serious risks including failure, infection, bleeding, numbness, weakness, nerve injury which could be transient or permanent, transient increase in pain, postdural puncture headache, injectate-related side effects such as contrast allergy, and effect of steroids [11]. For thoracic procedures and other structural injury, depending up on the level of injection, pneumothorax should be discussed and documented.
It is advisable to use only non-particulate steroids for cervical and thoracic transforaminal epidurals. Risk of serious neurologic complications and thromboembolic events in case of using particulate steroid [11, 13].
Sedation is best avoided to have real-time feedback. Discussion of sedation and its complications as well as method of sedation should be documented [11].
Preparation
Sterile environment
Appropriate equipment to perform the procedure must be checked
X ray/US machine with operators who have had appropriate training to use them safely
Injecting medications
Patient positioning
Preferably no sedation or, if required, very minimal sedation where the clinician maintains constant verbal contact with the patient throughout the procedure.
