Ultrasound-Guided Cervical Selective Nerve Root Block 09, Ultrasound Nerv… · Ultrasound-Guided...

Copyright @ 2009 . Unauthorized reproduction of this article is prohibited.American Society of Regional Anesthesia and Pain Medicine

Ultrasound-Guided Cervical Selective Nerve Root BlockA Fluoroscopy-Controlled Feasibility Study

Samer N. Narouze, MD, MS,* Amaresh Vydyanathan, MD,* Leonardo Kapural, MD, PhD,*ÞDaniel I. Sessler, MD,Þ and Nagy Mekhail, MD, PhD*

Background and Objectives: Reports of intravascular injectionduring cervical transforaminal injections, even after confirmation bycontrast fluoroscopy, have led some to question the procedure’s safety.As ultrasound allows for visualization of soft tissues, nerves, and vessels,thus potentially improving precision and safety, we evaluated itsfeasibility in cervical nerve root injections.Methods: This is a prospective series of 10 patients who receivedcervical nerve root injections using ultrasound as the primary imagingtool, with fluoroscopic confirmation. Our radiologic target point was theposterior aspect of the intervertebral foramen just anterior to the superiorarticular process in the oblique view and at the midsagittal plane of thearticular pillars in the anteroposterior (AP) view.Results: The needle was exactly at the target point in 5 patients in theoblique view and in 3 patients in the AP views. The needle was within3 mm in all patients in the lateral oblique view and in 8 patients in the APview. In the remaining 2 patients, the needle was within 5 mm from theradiologic target. In 4 patients, we were able to identify vessels at theanterior aspect of the foramen, whereas 2 patients had critical vessels atthe posterior aspect of the foramen, and in 1 patient, this artery continuedmedially into the foramen, most likely forming or joining a segmentalfeeder artery. In both cases, the vessels might well have been in thepathway of a needle correctly positioned under fluoroscopic control.Conclusions: Our case series shows the feasibility of using ultrasoundimaging to guide selective cervical nerve root injections. It may facilitateidentifying critical vessels at unexpected locations relative to the in-tervertebral foramen and avoiding injury to such vessels, which is theleading cause of the reported complications from cervical nerve rootinjections. A randomized controlled trial to compare the effectivenessand safety of ultrasound imaging against other imaging techniquesseems warranted.

(Reg Anesth Pain Med 2009;34: 343Y348)

Cervical radicular pain manifests as pain shooting down theupper extremity caused by irritation of the cervical spinal

nerves as they exit the neural foramina. The prevalence is about1 per 1000 members of the adult population and can be disablingto affected individuals.1 Although conservative therapy, usingexercises and analgesics, improves symptoms, its success isvariable.2,3 Failure of conservative therapy warrants alternatives,either surgery or cervical epidural injections.

Surgery remains the mainstay of treatment. Althoughstudies show its efficacy in relieving symptoms over the shortterm, its long-term efficacy is unclear.4 Moreover, cervical spinesurgery has an approximately 4% incidence of serious acutecomplications and requires hospitalization.5 The alternative iscervical epidural steroid injections, which provide good short-term symptom relief.6 The low incidence of major complications(G1% as reported by the Bone and Joint Decade 2000Y2010 TaskForce on Neck Pain and Its Associated Disorders)5 combinedwith ease of administration makes them an attractive option.

The spinal nerve occupies the lower part of the foramenwith the epiradicular veins occupying the upper part. Theradicular arteries arising from the vertebral, ascending cervical,and deep cervical arteries lie in close approximation to the spinalnerve. Traditionally, cervical transforaminal injections havebeen performed under fluoroscopic guidance.7 Real-timefluoroscopy with contrast injection is necessary to minimizeintra-arterial injections. But even with strict guidelines, multipleinstances of unintentional intra-arterial injections with resultantspinal cord injury have been reported.8,9 For example, Wallaceet al10 reported 2 cases of vertebral artery dissection and ad-vocated using a computed tomographyYguided technique toimprove the safety of the procedure. This has led some prac-titioners to question the use of this procedure and whether thebenefits outweigh the risks.11,12

The use of ultrasound imaging to facilitate nerve blocks hasincreased recently. Ultrasound allows visualization of softtissues, as well as nerves and vessels, and also permits vi-sualization of the injectate around the nerve.13,14 Unlike fluo-roscopy and computed tomography, ultrasound does not exposethe patients or personnel to radiation, and the image can beperformed continuously while the injectate is visualized in realtime, perhaps increasing the precision of injection. Importantly,ultrasound allows visualization of spinal nerves and vesselsand thus has the potential to improve safety by decreasing theincidence of injury or injection into nearby vasculature. Wetherefore designed this study to examine the feasibility of per-forming cervical nerve root injections under real-time ultra-sound guidance.

MATERIALS AND METHODSThis pilot study was approved by our institutional review

board, and written informed consent was obtained from allpatients. We enrolled 10 consecutive patients with cervicalradiculopathy supported by either magnetic resonance imagingor electromyographic findings, each of whom failed at least6 months of conservative therapy. Those patients were referredto our institute for diagnostic and/or therapeutic cervical se-lective nerve root block. The procedure was performed withultrasonography as the primary imaging tool and with fluoro-scopic confirmation. Patients with severe cervical spinal stenosisor neuralgic deficits were excluded from the study.

ULTRASOUND ARTICLE

Regional Anesthesia and Pain Medicine & Volume 34, Number 4, July-August 2009 343

From the *Pain Management Department and †Department of OutcomesResearch, Anesthesiology Institute, Cleveland Clinic, Cleveland, OH.Accepted for publication October 9, 2008.Address correspondence to: Samer N. Narouze, MD, MS, Pain Management

Department, Cleveland Clinic Foundation, 9500 Euclid Ave C25,Cleveland, OH 44195 (e-mail: [email protected]).

Copyright * 2009 by American Society of Regional Anesthesia and PainMedicine

ISSN: 1098-7339DOI: 10.1097/AAP.0b013e3181ac7e5c


With patients lying in the lateral decubitus position,ultrasound examinations were performed using a standardultrasound device (Philips HD11-XL, Philips Medical Systems,Andover, MA) and a high-frequency linear array transducer(3Y12 MHz). Skin was prepared with povidone-iodine, and strictsterile precautions were observed throughout.

The transducer was applied transversely to the lateral aspectof the neck to obtain a transverse axial view. First, the cervicalspinal level was determined by identifying the transverse processof the seventh and sixth cervical vertebrae (C7 and C6). Theseventh cervical transverse process (C7) differs from the levels

above by having a rudimentary anterior tubercle and a prominentposterior tubercle.15 By moving the transducer cranially, thetransverse process of the sixth cervical spine can be visualized,with its characteristic sharp anterior tubercle (Figs. 1A, B);thereafter, the consecutive cervical segments can be easilyidentified.

Another way to determine the cervical spinal level is byfollowing the vertebral artery, which runs anteriorly at the C7level before it enters the foramen of C6 transverse process inabout 90% of cases. However, it enters at C5 or higher in theremaining cases,16 and this was the case in one of our patients. If

FIGURE 1. A, Axial transverse ultrasound image showing the sharp anterior tubercle (at) of the C6 transverse process (C6 TP). Nindicates nerve root; CA, carotid artery; pt, posterior tubercle. Solid arrows point to the needle in place at the posterior aspect of theintervertebral foramen. B, Illustration showing the relevant anatomy at C6 level and the orientation of the ultrasound transducer.

FIGURE 2. A and B, Axial transverse ultrasound images showing the anterior tubercle (at) and the posterior tubercle (pt) of the C5transverse process as the ‘‘2-humped camel’’ sign. N indicates nerve root; CA, carotid artery. Solid arrows are pointing to the needle inplace at the posterior aspect of the intervertebral foramen.

Narouze et al Regional Anesthesia and Pain Medicine & Volume 34, Number 4, July-August 2009

344 * 2009 American Society of Regional Anesthesia and Pain Medicine


doubt remains about the spinal level and as the patient is in thelateral decubitus position, one may obtain a longitudinal midlinescan by applying the transducer vertically in the midline over thecervical spinous processes and start counting from cranial tocaudal (C1 arch lacks a spinous process). Once the appropriatespinal level is identified, the transverse axial view is obtained,and a 22-gauge, blunt-tip needle can be introduced just lateralto the lateral end of the transducer and advanced, from pos-terior to anterior, in-plane with the ultrasound beam under real-

time ultrasound guidance to target the corresponding cervicalnerve root (from C3 to C8) at the foraminal opening betweenthe anterior and posterior tubercles of the transverse process,which can be easily identified as the B2-humped camel[ sign(Figs. 2A, B). After placement of the needle, but beforeinjection, needle position was verified by anteroposterior (AP)and oblique lateral fluoroscopic images. Plain radiographs wereread by another physician experienced in fluoroscopy-guidednerve root blocks, and the needle was adjusted if necessary.

Our radiologic target point was the posterior aspect of thecorresponding intervertebral foramen just anterior to thesuperior articular process in the oblique view and halfwaybetween the medial and lateral borders of the articular pillars inthe AP view.

The position of the needle as placed by ultrasound wasconsidered accurate when the distance to the radiologic targetpoint was within 5 mm.We based this distance on the results of astudy concerning the spread of contrast agent during cervicalmedial branch block17; furthermore, Eichenberger et al18

considered this distance adequate in ultrasound-guided thirdoccipital nerve block. Displacement of the needle from thetarget point was quantified after correction for the magnificationeffects.

After proper needle placement was confirmed, 0.5 mL ofcontrast was injected under real-time fluoroscopy with digitalsubtraction to exclude intravascular injection. Then, we injected2 mL 1% lidocaine for diagnostic blocks or 2 mL of a mixtureof dexamethasone (8 mg) and 1% lidocaine for therapeuticblocks. All injections were performed under real-time ultraso-nography. Neurologic examination and sensory assessment wereperformed 30 mins after the block by testing pinprick and coldsensations.

RESULTSTen patients (8 women and 2 men) were enrolled in the

study, with a median age of 49 years. (range, 31Y54 years). Themedian body mass index was 25 kg/m2 (range, 21Y34 kg/m2).

FIGURE 3. A and B, Axial transverse ultrasound images showing the sharp anterior tubercle (at) of the C6 transverse process and thevertebral artery (VA) is anterior. N indicates nerve root; CA, carotid artery; pt, posterior tubercle. Solid arrowheads point to the needle inplace at the posterior aspect of the intervertebral foramen.

FIGURE 4. Axial transverse ultrasound image with pulsed-waveDoppler assessment showing arterial perfusion in a small vesselthat is located at the anterior aspect of the intervertebral foramen.N indicates nerve root; VA, vertebral artery; at, anterior tubercle;pt, posterior tubercle.

Regional Anesthesia and Pain Medicine & Volume 34, Number 4, July-August 2009 Ultrasound-Guided Cervical Nerve Root Block

* 2009 American Society of Regional Anesthesia and Pain Medicine 345


In all 10 cases, we were able to identify the cervicaltransverse process in the transverse axial view with the anteriorand posterior tubercles as hyperechoic structures, the classic 2-humped camel sign, and the hypoechoic round or oval nerve rootin-between. The cervical spinal level was correctly identified inall cases as confirmed by fluoroscopy. In 1 patient, the vertebralartery was anterior at C6, and it entered the foramen at C5 level(Fig. 3).

The needle was exactly at the target point in 5 of 10 patientsin the lateral oblique view and in 3 of 10 patients in the AP view(as we tend not to advance the needle too medially into theforamen, and the needle tip was lateral to the midsagittal plane ofthe articular pillar in the AP view). The needle was within 3 mmof the radiologic target in all patients in the lateral oblique viewand in 8 patients in the AP view. In the other 2 patients, theneedle was within 5 mm from the radiologic target (at theexternal foraminal opening).

In 4 patients, we were able to identify radicular arteries atthe anterior aspect of the foramen (Fig. 4), whereas 2 patientshad arterial vessels in close proximity to the posterior aspectof the foramen (at C6 and C7), and in 1 patient (C6), this artery(1Y1.5 mm in diameter) continued medially into the foramen,most likely forming or joining a segmental feeder artery(Figs. 5A, B). In both cases, these vessels were in the pathwayof a needle placed correctly under fluoroscopy alone and couldeasily have been injured. The transducer was moved slightlycephalad until those vessels disappeared as they were placedposteriorly and inferiorly relative to the intervertebral foramen,and the needle was placed safely under real-time ultrasono-graphic guidance to stop just at the external opening of theforamen to avoid injury to such vessels.

All patients developed decreased cold and pinpricksensations along the corresponding dermatome in 30 mins.

DISCUSSIONUltrasound imaging has revolutionized the field of regional

anesthesia and is rapidly becoming the technique of choice inmany centers.19 The available outcome data suggest thatultrasound guidance shortens onset time, improves blocksuccess rates, and increases patient satisfactionVall withoutincreasing block-related complications.20Y23 In contrast, ultra-sound guidance remains a technique in evolution for chronicpain management. Initial reports demonstrate its feasibility inperforming stellate ganglion block,24,25 third occipital nerveblock,18 cervical and lumbar facet joint injections,26,27 lumbarmedial branch block,28,29 and periradicular injections.30

The advantages of ultrasonography over fluoroscopyinclude lack of radiation exposure to both the patient (especiallywith repeated procedures) and the operator and real-timevisualization of soft tissues (nerves, muscles, vessels, etc),visualization of needle tip advancement relevant to surroundingstructures, and visualization of local anesthetic spread. Themajor shortcomings of ultrasonography with respect to spineinjections are the bony artifacts and the limited resolution atdeep levels, which may prevent good visualization of small-gauge needles. Ultrasonography may be particularly helpful inthe cervical area because a multitude of vessels and other vitalstructures are compacted in a limited area.31

Ma et al32 in a survey of 1036 consecutive extraforaminalcervical blocks showed a complication rate of 1.64%, but theyalso reported 6 patients with transient neurologic deficits and 1patient with global amnesia. There have been reports of fatalcomplications in the literature as a result of vertebral arteryinjury.10,33 But the more commonly reported serious complica-tions were related to intravascular injections causing infarctionof the spinal cord and the brainstem.8,9,34Y36 The mechanism ofinjury was contended to be vasospasm or the particulate natureof the steroid injectate with embolus formation after uninten-tional intra-arterial injection.8,9

Furman et al37 showed a 19.4% incidence of unintentionalintra-arterial injections during transforaminal cervical epiduralsteroid injections. The use of aspiration of blood was only 46%sensitive for detection, and real-time contrast fluoroscopy wasdeemed necessary to detect unintentional intravascular injec-tions. Baker et al9 showed that even real-time contrast fluoros-copy may be insufficient and recommended digital subtractionangiography for detection of unintentional intravascular injec-tion. In our small case series, we had no unintentional intravas-cular injections as confirmed by digital subtraction angiography.

Current guidelines for cervical transforaminal injectiontechnique involve introducing the needle under fluoroscopicguidance into the posterior aspect of the intervertebral foramenjust anterior to the superior articular process in the oblique viewto minimize the risk of injury to the vertebral artery or the nerveroot.7 Despite strict adherence to these guidelines, adverseoutcomes have been reported.8,9 Complications may result fromthe presence of a critical feeder vessel to the anterior spinalartery in the posterior aspect of the intervertebral foramen that isin the pathway of the needle.38 Ultrasonography may be useful insuch circumstances as it permits visualization of vessels.Galiano et al39 described the use of ultrasound in performingcervical periradicular injections in cadavers. They were unableto comment on the relevant blood vessels in the vicinity of the

FIGURE 5. A, Axial transverse ultrasound image with color Doppler showing a small vessel at the posterior aspect of the intravertebralforamen, which continued medially into the foramen (B). at indicates anterior tubercle; pt, posterior tubercle.




vertebral foramen, and this raised some concerns about thesafety of performing the procedure with ultrasound at thattime.40 In fact, in 2 of our 10 patients, there were vessels at theposterior aspect of the foramen that could be potentially injuredin the path of a correctly placed needle, if the procedure weredone under fluoroscopy. These findings reconfirmed the work byHuntoon38 on cadavers. He was able to show that the ascendingand deep cervical arteries may contribute to the anterior spinalartery. More than 20% (21/95) of the foramina dissected hadeither the ascending or deep cervical artery or a large branchwithin 2 mm of the needle path for a cervical transforaminalprocedure. One third of these vessels were spinal branches thatentered the foramen posteriorly, potentially forming a radicularor a segmental feeder vessel to the spinal cord.

In a single-cadaver-dissection study, Hoeft et al41 showedthat radicular artery branches from the vertebral artery lie overthe most anteromedial aspect of the foramen, whereas those thatarise from the ascending or deep cervical arteries are of greatestclinical importance as they course medially, transversing theentire extent of the foramen. It is for this reason that we avoidadvancing needles deep through the foramen, instead stopping atthe external foraminal opening. Although ultrasonographyprovides more information about vascular structures thanfluoroscopy, it can nonetheless be difficult to trace the vesselsdeep in the foramen as they course toward the spinal vessels.Thus, although we were successful in monitoring the spread ofthe injectate around the cervical nerve, we were not able tomonitor the spread of the injectate through the foramen, if any,into the epidural space (because of the bony dropout artifact ofthe transverse process). We therefore refer to our approach as aBcervical selective nerve root block[ rather than cervicaltransforaminal epidural injection (Fig. 6).

Although our case series shows the feasibility of usingultrasound imaging to guide selective cervical nerve rootinjections and to visualize critical vessels in the vicinity of theexternal cervical intervertebral foramen, use of ultrasoundimaging may be difficult in certain patients and requires some

experience to adequately use it for these injections. Our study isalso limited in that the assessment of visualization of landmarkswas made by only one of the authors of this study (S.N.) and maybe subject to bias. We emphasize that the inability to visualizecritical vessels at the posterior aspect of the neuroforamen in theremaining patients does not necessarily mean they do not exist.Rather, they may be they too small to be detected by the currentultrasound technology. Although we were able to monitor thespread of the injectate in real time, ultrasonography may notreliably detect tiny intravascular injections that still can lead toneurologic injury.

In summary, ultrasound imaging can be used to obtain well-defined images of the cervical neural foramina with real-timevisualization of the spinal nerves and vessels and maypotentially improve the safety of the technique. It may facilitateidentifying anomalous critical vessels at unexpected locationsrelative to the intervertebral foramen and avoiding injury to suchvessels, which is the leading cause of the reported complicationsfrom cervical nerve root injections. With cervical selective nerveroot block (cervical transforaminal epidural injection), there istruly no safe zone; however, there may be a safer tool. Arandomized controlled trial to compare the effectiveness andsafety of ultrasound imaging against other imaging techniquesseems warranted to elaborate on its actual clinical utility inperforming cervical nerve root injections.

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Regional Anesthesia and Pain Medicine & Volume 34, Number 4, July-August 2009 Ultrasound-Guided Cervical Nerve Root Block

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