Anatomy

The anterior spinal nerves of the cervical plexus emerge from the neural foramina of C1 to C4 in the lateral neck between the anterior and posterior tubercles of the respective transverse processes. They then pass along the lateral aspect of the longus colli and longus capitis muscles and the medial aspect of the levator scapulae and middle scalene muscles. Note that there is no anterior scalene muscle above the level of C4.

Transverse View of the Neck at the C4 Level Picture modified from the Visible Human Project Picture provided by Armbruster, Eichholz and Notheisen

Schematic Illustration of Key Anatomical Structures at the C4 Level LCaM = Longus capitis muscle LCoM = Longus colli muscle LSM = Levator scapulae muscle MSM = Middle scalene muscle SCMM = Sternocleidomastoid muscle Picture provided by Armbruster, Eichholz and Notheisen

The nerves of the cervical plexus run through the deep cervical fascia and enter the "Cervical Nerves Pathway" (CNP) which is the space between the deep cervical fascia (covering the paravertebral muscles) and the superficial cervical fascia (covering the sternocleidomastoid muscle)

Schematic Illustration of the Deep and Superficial Fascia of the Neck

CNP = Cervical nerves pathway DCF = Deep cervical fascia SCF = Superficial cervical fascia Picture provided by Armbruster, Eichholz and Notheisen

Nerves of the cervical plexus pass from medial to lateral underneath the sternocleidomastoid muscle, and pierce the superficial cervical fascia at the lateral edge, corresponding to Erb's point.

As shown in the figure below, cutaneous branches that come off the cervical plexus are:

Cutaneous branches of the cervical plexus provide sensory innervation to the skin of the anterolateral neck, the surrounding muscles and connective tissue.

Muscular branches of the cervical plexus are:

1. the phrenic nerve, from C3 to C5 (primarily C4), innervates the diaphragm and pericardium
2. ansa cervicalis innervates chin muscles above the hyoid bone and strap muscles of the neck below
3. branches to the anterior and middle scalene muscles

It is important to note that the vagal nerve (X), the glossopharyngeal nerve (IX) and sensory branches of sympathetic nerves (from superior cervical ganglion) provide sensory innervation to the intima of the carotid artery and the glomus organ.

Thus blockade of the cervical plexus only provides sensory anesthesia to the lateral neck, but not to the carotid artery and glomus organ. For carotid endarterectomy surgery, it is necessary to instill local anesthetic in the carotid sinus region to prevent bradycardia independent of the cervical plexus block.

Superficial Cutaneous Branches of the Cervical Plexus

GAN = Great auricular nerve LON = Lesser occipital nerve SCMM = Sternocleidomastoid muscle SCN = Supraclavicular nerves TCN = Transverse cervical nerve Picture modified from Grays Anatomy Picture provided by Armbruster, Eichholz and Notheisen

Scanning Technique

Position the patient supine and turn the head slightly to the contralateral side.

After skin and transducer preparation (see transducer preparation section), place a linear high frequency 13 to 18 MHz transducer firmly on the neck in the axial, oblique plane to obtain the best possible transverse view of the cervical plexus.

Optimize machine imaging capability. Select appropriate depth of field (usually 3 to 4 cm), focus range (usually 2-3 cm) and gain.

Perform a trace-back of the cervical spine in order to visualize the corresponding nerve roots

Transducer Position Over the Posterior Cervical Triangle for Trace Back Maneuver to Identify the Respective Nerve Roots

Picture provided by Armbruster, Eichholz and Notheisen

Anatomical Correlation

Ultrasound Beam Projection Over the Cervical Nerves Pathway at C4 level

Picture provided by Armbruster, Eichholz and Notheisen

Nerve Localization

Perform a systematic anatomical survey to identify the origin of the nerve roots exiting the neural foramina and the respective vertebral transverse processes.

Start scanning at the C7 level as this transverse process has no anterior tubercle thus is easily identified. Recognize the hyperechoic bony outline (reflex of the covering periosteum) with underlying bony acoustic shadowing.

Then scan cephalad using the trace back method to identify the nerve roots of C6 to C3 and their respective transverse processes.

At the C4 level and above, the transverse processes more difficult to identify because the anterior and posterior tubercles are smaller and close together.

Then focus the ultrasound examination at the level of C4. The carotid artery bifurcation is at the level of C4 in most of the patients. Use it as additional sonographic landmark for C4 identification.

Sonogram of the C4 Nerve Root (Without Legend) Picture provided by Armbruster, Eichholz and Notheisen

Sonogram of the C4 Nerve Root (With Legend) C4 = Spinal nerve C4 CNP = Cervical Nerves Pathway ECA = External carotid artery ICA = Internal carotid artery SCMM = Sternocleidomastoid muscle TP = Transverse process of C4

Needle Insertion Approach

After identifying the Cervical Nerves Pathway (visualizing the C4 nerve root arriving in the Cervical Nerves Pathway), insert the needle using the out-of-plane (OOP) or in-plane (IP) approach.

The endpoint of needle placement for both OOP and IP approach is to keep the needle between superficial and deep cervical fascia. It is not recommended to advance the needle tip directly towards the carotid artery.

We prefer the OOP approach because this is a more direct approach and the shortest distance to reach the Cervical Nerves Pathway.

Exercise utmost care by visualizing the needle tip during the OOP technique to prevent unintended deep cervical injection.

Illustration of an Out of Plane Approach

Illustration of an In Plane Approach

Picture provided by Armbruster, Eichholz and Notheisen

Local Anesthetic Injection

Out of Plane (OOP) Approach

For the OOP approach, the goal is to maintain the needle tip between the superficial cervical fascia and the deep cervical fascia during injection.

The use of hydrodissection allows identification of several horizontal interseptal spaces.

The goal is to fill the Cervical Nerves Pathway (CNP) homogeneously and completely. Thus the Cervical Plexus Block can also be described as C2-C4 Compartment Block.

During a 20-mL local anesthetic injection, the CNP expands from 0.5 cm to approximately 1-1.5 cm in diameter.

Often one needle pass is adequate if the observed local anesthetic spread is deemed optimal.

It is advantageous to observe local anesthetic spread towards the carotid artery.

Illustration to Show Local Anesthetic Injection Using the OOP

LA = Local anesthetic (blue) Picture provided by Armbruster, Eichholz and Notheisen

In Plane (IP) Approach

Position and advance the needle medially from the lateral border of the sternocleidomastoid muscle into the CNP. Again apply hydrodissection to enter the CNP and fill this space with 20 mL of local anesthetic. It may be necessary to reposition the needle tip during injection to ensure even spread within the CNP.

It is important to constantly visualize the needle tip and local anesthetic spread during injection.

It is not not recommended to advance the needle tip directly towards the carotid artery.

Illustration of Local Anesthetic Injection Using the IP Approach

LA = Local anesthetic (blue) Picture provided by Armbruster, Eichholz and Notheisen

Clinical Pearls

Phrenic Nerve

Diaphragmatic paresis or palsy is noted in ~100% of the patients following a cervical plexus block. Most patients can tolerate diaphragmatic paresis or palsy without clinical symptoms. However, the following is a list of absolute or relative contraindications of a Cervical Plexus Block:

• contralateral diaphragmatic paresis
• morbid obesity
• partial respiratory failure, regardless of cause
• non-cooperative patients
• It is not required to visualize the phrenic nerve before performing a Cervical Plexus Block as blockade of this nerve is unavoidable.
• If you seek to identify the phrenic nerve, perform the trace back maneuver and look for a hypoechoic oval structure moving across the anterior scalene muscle. During trace back (from caudad to cephalad) the phrenic nerve runs from the medial to lateral aspect of the anterior scalene muscle and receives contributions from the C4 and C5 nerve roots.

Illustration to Outline the Course of the Phrenic Nerve

ASM = Anterior scalene muscle PN = Phrenic nerve Picture modified from Grays Anatomy Picture provided by Armbruster, Eichholz and Notheisen

Sonogram Showing the Phrenic Nerve at the C7 Level (Without Legend) Picture provided by Armbruster, Eichholz and Notheisen

Sonogram Showing the Phrenic Nerve at the C7 Level (With Legend) C5 = Nerve root C5 C6 = Nerve root C6 C7 = Nerve root C7 ASM = Anterior scalene muscle CA = Carotid artery IJV = Internal jugular vein MSM = Middle scalene muscle PN = Phrenic nerve SCMM = Sternocleidomastoid muscle TP = Transverse process of C7 VA = Vertebral artery VV = Vertebral vein

Diaphragmatic function can be assessed by ultrasound in B-Mode and M-Mode. Use FAST 1 position or FAST 3 position respectively:

Diaphragm in M-Mode, FAST 1 Position, Normal Function D = Diaphragm L = Liver S = Spine

Diaphragm in M-Mode, FAST 1 Position, Paresis D = Diaphragm

Picture provided by Armbruster, Eichholz and Notheisen

Image Gallery

Sonographic Anatomy at the C7 Level, Right Side	Sonographic Anatomy at level the C6, Right Side
Sonographic Anatomy at the C5 Level, Right Side	Sonographic Anatomy at the C4 Level, Right Side
Sonographic Anatomy at the C3 Level, Right Side	Sonographic Anatomy at the C2 Level, Right Side

Simple "Neuro-Monitoring" in Patients with CPB


Picture provided by Armbruster, Eichholz and Notheisen

Video Gallery

Selected References

Anatomy of the Cervical Plexus

• Winnie AP et al. Interscalene cervical plexus block: A single-injection technic; Anesthesia and Analgesia 1975; 54 (3): 370-375

Anatomy Scalene Muscles

• Usui Y et al. An anatomical basis for blocking of the deep cervical sympathetic tract using an ultrasound-guided technique; Anesthesia and Analgesia 2010; 110: 964-968

Complications of Cervical Plexus Blocks

• Pandit JJ et al. Superficial or deep cervical plexus block for carotid endarterectomy: a systematic review of complications; British J Anesthesia 2007; 99 (2): 159-169

Advantage of Cervical Plexus Blocks

• GALA Trial Collaboratorive group. General anaesthesia versus local anaesthesia for carotid surgery; Lancet 2008; 372: 2213-2142

Injection Technique

• Herring A; The ultrasound guided superficial cervical plexus block for anesthesia and analgesia in emergency care settings; Am J Emerg Med; 2012; 30; 1263-1267
• Martusevicius R; Ultrasound guided locoregional anaesthesia for carotid endarterectomy; Europ J Vasc Endovasc Surg; 2012; 44; 27-30