Cervical epidural steroid injection (CESI) has been performed to treat the patient with neck or upper limb pain, which is caused by various cervical pathologies by eliminating chemical mediators in epidural spaces and around nerve root and dorsal root ganglion. CESI is widely indicated and regarded to be effective method because the cervical pathologies frequently begin with cervical disc degradation/ annular tear and its subsequent irritation onto nervous tissues such as sinuvertebral nerves over ventral epidural space, dura, and posterior longitudinal ligaments and nerve root. This is correspondent to lumbosacral epidural injection as to low back and/or leg pain secondary to lumbosacral diseases [1-3].

But unlike lumbosacral epidural injection, there is concerns about high risk of side effects, sometimes devastating events such as brain damage, spinal cord infarct, and even death [4]. This potential side effects lead patients to be anxious about taking CESI and even physicians reluctant to conduct CESI and instead only to prescribe indirect and non-target specific treatment including medication or physical therapy instead of conducting seemingly dangerous procedure.

However, main physicians’ role is ranged over comprehensive processes including finding out and directly removing the cause of diseases. More target specific and direct approach is preferred. Even exact localization of pain source is less meaningful if only indirect and non-specific treatment method follows it. For example, it is not reasonable that sophisticated diagnostic tools such as magnetic resonance image or electrodiagnostic test are performed for only prescription of oral medication afterwards. Instead, pain physicians should choose the way to maximize the clinical efficacy and minimize the possible side effects by expanding their experiences and understandings about cervical pathologies, relevant anatomy, and technical consideration of CESI.

Therefore, this narrative review is written to explore the technical consideration of CESI in order to stress the clinical importance of CESI as target-specific conservative treatment for pain from cervical diseases.

Radicular pain over the upper extremity is usually caused by either irritation or compression on the dorsal root ganglion or the nerve root sheath. Thus, transforaminal CESI has been preferred over the interlaminar CESI because its theoretically closer proximity to the cervical pathology would facilitates more direct, optimized drug delivery around the main pain generators (Fig. 1) [5]. But transforaminal CESI, despite this advantage, has the concern for devastating side effects such as brainstem or upper spinal cord infarct due to embolus or thrombosis resulted from intraarterial needle penetration and occlusion or aggregated drug particles [6,7].

Figure 1. Demonstrates direction of needle approaches of interlaminar and transforaminal epidural injection as well as their related cervical spine structures. *Arrow: interlaminar needle approach; **arrow: transforaminal needle approach. a: vertebral artery; b: intervertebral disc; c: nerve root; d: cervical spinal cord; e: ligamentum flavum; f: facet joint.

To avoid serious side effects as mentioned above, it is recommended that needle should be approached over posterior aspect of neural foramen as much as possible, which helps to prevent the needle from penetrating vertebral and radiculo-medullary arteries and furthermore injecting medication. But according to Huntoon’s study, 22% of radicular arteries are placed within 2mm of conventional needle trajectory during posterior foraminal approach [8]. It means that it is impossible to entirely avoid needle violation. Thus, for safe procedure, use of soluble and non-particulate steroid is essential.

Needle advancement angle is another consideration for safe approach into neural foramen. The obtuser approach from vertical line than conventional approach, providing better visualization view of the superior articular process, is regarded to be safer because this leads the needle trajectory farther away from the vascular structures and closer to superior articular process than more acute conventional approach [9].

There have been reports stating that paramedian interlaminar CESI can achieve comparable clinical outcomes to transforaminal CESI even in the patients with radicular arm pain [10-15]. This is explained by that paramedian approach produces compatible or more effective drug delivery onto the ipsilateral ventral epidural spaces and around nerve root in comparison with transforaminal approach [16,17]. This result indicates that transforaminal CESI, a procedure regarded as hazardous, can be replaced by interlaminar approach, if the needle is advanced into ipsilateral side and allow for efficient drug spread into pain generator.

The sinuvertebral nerves located in the ventral epidural spaces might also trigger an axial neck or scapular pain. In lumbosacral disc diseases, the transforaminal approach is regarded to be more beneficial to the patients suffering from the axial back pain over the interlaminar approach since these transforaminal approach has the ability of the more accurate, closer needle advancements and direct transfer of the injected solutions over sinuvertebral nerves located ventral epidural spaces. But, during the cervical epidural injection, this transforaminal injection, routinely performed in supine, oblique fashion after targeting the posterior part of a neural foramen in order to avoid any vascular insult, would be supposed to be refrained from the intended proper transfer of the solutions over the ventral epidural space. A study comparing the clinical efficacy between interlaminar and transforaminal CESI in the patients with axial neck pain revealed that transforaminal injection expectedly had no significantly different advantage over interlaminar injection, which suggested that interlaminar CESI was more recommended in axial pain than transforaminal CESI, given the fact of closer relationship of transforaminal CESI to devastating side effects [18].

Of interlaminar CESI, the paramedian approach compared with midline approach has been acclaimed to be capable of direct transfer of medication over the ventral epidural space and dorsal root ganglion, which results in comparable clinical results to transforaminal approach for the cervical radicular pain. Several studies have already featured showed that the more frequent ipsilateral and ventral contrast filling pattern as well as and provided the better subsequent clinical efficacy after the paramedian injection than midline fashion for the cervical radicular pain. Therefore, this inherent technical property of paramedian approach could allow itself to be applied to the patients suffering from the pure axial neck pain [17,19].

Interlaminar approach is also associated with adverse events related to intrathecal needle invasion such as intrathecal hematoma, spinal cord injury and intrathecal drug administration. Loss of resistance that signals needle placement in epidural space after penetrating ligamentum flavum is sometimes unreliable because gap between ligamentum flavum may exist especially in lower cervical area, which is frequently used for interlaminar CESI [20]. Lateral view of C-arm fluoroscopy cannot always accurately determine whether needle tip is placed into epidural space because dorsal epidural space is shaped as triangle and ventral laminar line indicates only the peak area of triangular dorsal epidural space. Especially, paramedian placement of needle tip appears to penetrate the dural sac and placed inside thecal sac, even though needle is placed into dorsal epidural space accurately [21].

To avoid these problems, contralateral oblique (CLO) view is used which C arm detector is rotated contralaterally to ipsilateral needle placement to pain generator. The ipsilateral dorsal epidural space is clearly identified along with ventral laminar line visualized by CLO view, which enables physicians to recognize the depth to the dorsal epidural space during needle advancement and to avoid the needle penetration into thecal sac (Fig. 2) [22,23].

Figure 2. Demonstrates direction of C arm detector for lateral view and contralateral oblique (CLO) view when left paramedian interlaminar epidural injection is performed. Right CLO line is correspondent to left ventral laminar line and can visualize accurate needle depth. a: lateral view; b: CLO. *Needle approach.

There was a concern about optimal rotation angle of C arm for appropriate CLO view. A literature measured the angle between midsagittal line and ventral laminar line in midline and paramedian zone respectively. This study indicated that the more tilt of C arm detector from vertical line, establishing obtuser angle, during CLO was needed to optimally visualize the ventral laminar line for midline approach than paramedian approach [23].

Another technical consideration during interlaminar approach is the retro-ligamentous space of Okada, a potential space posterior to the ligamentum flavum that communicates with the bilateral facet joints. When a needle enters the space of Okada, a false-positive loss of resistance appears as if it had entered the epidural space. This misunderstanding cause wrong needle position and drug administration. Previous studies have reported incidences of unintended injection into the space of Okada during interlaminar epidural injection in the lumbar spine of 0.6-6.0% under fluoroscopic guidance. When the needle is identified to be located into the space of Okada determined by characteristic contrast flow, the needle should be advanced more anteriorly and penetrated through ligamentum flavum in order to be exactly placed into epidural space (Fig. 3) [24].

Figure 3. (A, B) Anteroposterior and lateral view respectively that show the contrast filling into right facet joint, which suggests that contrast spreads into space of Okada and further facet joint communicated with this space, instead of dorsal epidural space.

Radiation exposure is another barrier to choose the C-arm guided injection as treatment method. The consideration about more complexity of cervical spine and vascular anatomy and higher degree of technical difficulty compared with lumbosacral spine leads to more frequent and prolonged radiological exposure during cervical ESI. Thus, ultrasound (US) guided transforaminal injection has been regarded as substitute due to non-radiation exposure. US, in addition to avoiding radiation exposure, has advantages of providing real time image of vascular and nervous structures around neural foramen, which can help to prevent side effects. But the property of US, not penetrating the bony structure and therefore not visualizing intervertebral foramen, allows for only needle approach around anterior and posterior tubercle of transverse process. Ultimately, epidural drug spreading through transforaminal approach is not easily achieved, instead, periradicular injection is mainly done by US guidance.

Several studies demonstrated that US guided injection, obtaining comparable clinical results to C arm guided injection, notably showed no vascular uptake of injectate, while several cases of vascular uptake were observed in C arm guided injection [12,14,25,26]. This was explained by the results from direct observation of radiculo-medullary branches during US guided injection [26]. But these studies have debatable points. The participants with radicular pain, not axial pain were selected in these studies, who could be benefitted only by treatment around nerve root and did not necessitate epidural drug spreading, which might result in comparable outcome to C arm injection despite insufficient drug delivery into epidural space. US has a critical weakness that provide only cross-sectional view and therefore, is inferior to C arm with regard to revealing vascular uptake. No intravasation in ultrasound group might be from failure of detecting vascular uptake [27]. Therefore, in my opinion, it is still controversial to assure that US guided transforaminal injection can be substitute treatment method to C arm guided injection, in spite of advantage of no radiation exposure, especially in the patients with axial neck pain that might be from epidural pain sources and is superior in terms of avoiding intravasation.

Very frequently, a excessive fear for steroid usually used in epidural injection, widely spread among not only patients but even also physicians, is the main cause of reluctance to performing epidural injection. Aside from anxiety about possible steroid associated side effects, technical difficulty, and concerns for serious side effects of injections facilitate this phenomenon. In addition, due to widespread ignorance about side effects of and acceptability for oral medications, usually non-steroidal anti-inflammatory drugs (NSAIDs) are prescribed and taken by the patients for months or sometimes indefinitely without any resistance, instead of target specific treatment.

However, all medications have their unique side effects. Side effects of NSAIDs have been extensively reported including allergic, gastrointestinal, renal, and cardiovascular problems. NSAIDs increases the risks of gastrointestinal bleeding, with the large tendency in those with old age or taking aspirin [28-32]. Selective cyclo-oxygenase 2 inhibitors, closely related to cardiovascular side effects, is contraindicated in the patients with ischemic heart disease and should be cautiously used in the patients with risk factors such as hypertension, hyperlipidemia, and diabetes [30,31,33]. NSAIDs elevates blood pressure by blocking anti-hypertensive medication and by direct effects such as increased peripheral resistance and sodium retention, which was more remarkable in patients with hypertension [34]. Notably, NSAIDs contribute to a quarter of hospital admissions due to adverse drug reactions in older people [33].

Irrespective of types of medication, systemic drug administration is more associated with side effects than local treatment [35]. Oral intake of medication is limited for curing diseases themselves, therefore leading to long period systemic exposure, and further aggravates systemic side effects. As the pain physicians, more desirable is conducting disease specific treatment instead of purposeless repetition of prescribing medications. Making the effort to promote the skill and knowledge relevant to intervention and overcoming the barriers associated with technical difficulty enable them to provide the patients with more useful treatment option.

Cervical ESI is useful treatment for the patients with axial neck and/or arm pain from various cervical pathologies as lumbosacral epidural injection as to low back and/or leg pain. But unlike lumbosacral epidural injection, cervical epidural injection is reluctant to be conducted not only by patients but by physicians due to various reasons such as technical difficulty, anatomical consideration, and risk of serious side effects in addition to fear for steroid and radiological exposure.

Appropriate procedural application based on exact knowledge of relevant anatomical and technical considerations can facilitate its clinical usefulness as well as minimize side effects. As a results, this provides direct and target specific treatment instead of only prescribing indirect treatment and further give the patients good treatment opportunity, who would have undergone unnecessary surgery with untreated by only medication.

No potential conflict of interest relevant to this article was reported.