Scalp block and cervical plexus block techniques

INTRODUCTION — Scalp blocks and cervical plexus blocks are used for operative anesthesia and/or postoperative analgesia for a variety of surgeries. This topic will discuss the innervation of the scalp and neck, indications, techniques and drugs used for these blocks, and complications specific to each block. Equipment used, contraindications, and complications common to all nerve blocks are discussed separately. Nerve blocks for airway anesthesia for awake intubation and infraorbital and mental nerve blocks are also discussed separately. (See "Overview of peripheral nerve blocks" and "Assessment and management of facial lacerations", section on 'Facial nerve blocks' and "Awake tracheal intubation", section on 'Airway anesthesia'.)

SCALP BLOCK — Individualized, targeted nerve blocks of the scalp have evolved to become sophisticated and effective techniques compared with traditional local anesthetic (LA) infiltration [1-4].

Applications of scalp blocks — Scalp nerve blocks are useful for awake and routine craniotomies, deep brain stimulation, stereotactic procedures, craniosynostosis repair in pediatric patients, and for treatment of chronic pain syndromes of the head and neck [1-3].

Scalp blocks are performed for craniotomy in order to blunt the hemodynamic response to skull pinning and to reduce postoperative pain [4-6]. Preoperative scalp block can reduce intraoperative opioid requirement, which can facilitate early postoperative neurologic assessment [5-7]. As an example, a 2013 meta-analysis of seven trials with 320 patients found a reduction in pain scores up to 12 hours after craniotomy and a reduction in cumulative opioid requirements over the first 24 postoperative hours with the use of scalp nerve blocks [1]. (See "Anesthesia for craniotomy in adults", section on 'Postoperative pain control'.)

Anatomy — Four branches of the trigeminal nerve (TN) and two branches of the cervical nerve roots C2 and C3 provide innervation to the anterior and posterior scalp (figure 1) [2,3]. The supraorbital and supratrochlear nerves are sensory nerves that innervate the forehead and upper eyelids. They are derived from the ophthalmic division (V1) of the TN. The zygomaticotemporal nerve is from the maxillary division (V2) of the TN and supplies a small area lateral to the outer canthus of the eye. The auriculotemporal nerve is a branch of the mandibular division (V3) of the TN and provides sensation anterior and superior to the ear. The greater occipital nerve arises from the dorsal ramus of C2 and ascends through the posterior scalp medial to the occipital artery. The lesser occipital nerve originates from the ventral rami of C2 and C3 and courses upward from the posterior neck to innervate the scalp behind the ear (figure 2) [2,3].

Scalp block technique — Six nerves are blocked on each side for complete scalp block. This block is performed with long-acting LA (eg, bupivacaine 0.25 or 0.5%, or ropivacaine 0.2 or 0.5%) using a 1.5-inch, 25- or 27-gauge needle, using the following techniques (figure 3):

Supraorbital and supratrochlear nerve blocks — With the patient in supine position, palpate the supraorbital notch in the medial third of the supraorbital ridge. The notch is usually located directly above the midpoint of the pupil (figure 4). Insert the needle 0.5 to 1 cm deep, perpendicular to the skin, until bone is contacted. Withdraw the needle slightly, and after negative aspiration, inject 3 mL of LA to block the supraorbital nerve. Redirect the needle medially under the skin, advance approximately 1 cm, and after negative aspiration, inject 2 to 3 mL of LA to block the supratrochlear nerve. If paresthesia is elicited, the needle should be repositioned prior to injection.

Auriculotemporal nerve block — The following technique minimizes the chance of anesthetizing the facial nerve, which runs near the auriculotemporal artery at the level of the tragus [8].

Palpate the superior temporal artery 1 cm cephalad to the level of the tragus of the ear. Insert the needle perpendicular to the skin, just posterior to the temporal artery. Loss of resistance or a click can usually be felt when the needle passes through the temporalis fascia, at a depth of 1 to 2 cm. After negative aspiration, inject 2 mL of LA below the fascia and another 1 mL superficial to the fascia as the needle is withdrawn.

Zygomaticotemporal nerve block — Palpate a groove along the zygomatic arch just lateral to the lateral canthus of the eye. At that point, insert the needle perpendicular to the skin and advance until loss of resistance or a click is felt as the needle passes through the temporalis fascia. After negative aspiration, inject 1 to 2 mL of LA below the fascia.

Greater occipital nerve block — Palpate the occipital artery midway between the occipital protuberance and the mastoid process. Insert the needle medial to the artery and, after negative aspiration, inject 5 mL of LA.

Lesser occipital nerve block — Insert the needle 2.5 cm lateral to the injection point for the greater occipital block and, after negative aspiration, inject 5 mL of LA.

Complications of scalp block — The auriculotemporal nerve block can cause transient facial nerve paralysis [8,9]. Facial nerve block should be self-limited and should resolve as the scalp block wears off, but it may complicate assessment of facial nerve trauma related to surgery. The incidence of facial nerve block may be reduced by minimizing the volume of LA injected for auriculotemporal block and by performing the block as described above [8].

CERVICAL PLEXUS BLOCKS — Superficial and deep cervical plexus blocks are the peripheral nerve blocks used for neck surgery. An intermediate cervical plexus block has also been described. These blocks can be used as primary anesthetics for carotid endarterectomy, where neurologic monitoring of an awake patient may identify cerebral thromboembolic or ischemic events. In this setting, coverage from a cervical plexus block may be variable and may require supplemental local anesthetic (LA) infiltration by the surgeon. (See "Anesthesia for carotid endarterectomy and carotid stenting", section on 'Local/regional anesthetic techniques'.)

Cervical plexus block can also be utilized for postoperative pain control after thyroid, parathyroid, trachea, and medial clavicle surgeries; cervical spine procedures; and after other neck procedures [10-12].

Deep cervical plexus blocks, especially landmark-based techniques, are rarely performed, for the following reasons:

●The incidence of significant complications (eg, vertebral artery or subdural injection of LA) is higher with deep block compared with superficial block. (See 'Complications' below.)

●Inadequate block is more common with deep cervical plexus block than with superficial block [13].

●Superficial cervical plexus block supplemented with intraoperative neck infiltration is often sufficient to provide postoperative analgesia.

●Deep cervical plexus block is more difficult to perform than superficial block.

Anatomy — The cervical plexus is composed of the ventral rami of the first four cervical spinal nerves (ie, C1 through C4). The ventral rami of C2 through C4 emerge from the posterior border of the sternocleidomastoid muscle (SCM) (figure 5). There are four cutaneous branches of the cervical plexus, all of which are derived from C2 to C4. They are the lesser occipital nerve, the greater auricular nerve, the transverse cervical nerve, and the supraclavicular nerve. The cervical plexus supplies the skin of the anterolateral neck and posterolateral scalp, the skin around the ear, and the muscles of the neck, including the scalenes and strap muscles (figure 6). The cervical plexus also innervates the diaphragm via the phrenic nerve (C3, C4, C5) [13,14].

Cervical plexus blocks are defined by injections relative to the two layers of the deep cervical fascia (ie, the superficial, or investing, layer and the deep layer). A superficial cervical plexus block involves injection superficial to the investing layer, the intermediate block involves injection between these two layers, and the deep block involves injection deep to the deep layer (image 1) [15].

Cervical plexus block technique

Superficial cervical plexus block technique — Superficial cervical plexus block is easier to master than deep cervical plexus block, is associated with few complications, and does not usually require ultrasound guidance. Nevertheless, we prefer ultrasound guidance because it can provide more precise deposition of LA in the posterior fascial plane of the SCM with visualization of the needle through the SCM. Ultrasound also allows identification of central vessels, allows navigation away from more superficial vessels (eg, external jugular vein), and may help avoid LA spread to the brachial plexus in the interscalene groove.

The patient is positioned supine, with the head slightly away from the side to be blocked.

●Ultrasound guidance – Ultrasound guidance can be used, with the following technique:

•Place a small, linear ultrasound probe in transverse orientation at the posterior border of the SCM, midway between the mastoid process and the C6 transverse process (figure 7 and picture 1). Visualize the posterior fascia of the SCM. The cervical plexus, when it can be seen, may be visualized as a collection of small hypoechoic (black) ovals, immediately deep or lateral to the posterior border of the SCM.

•Insert the needle in plane to the transducer (picture 2) with a lateral to medial trajectory and advance until the tip is adjacent to the nerves (image 2). After negative aspiration, inject 10 mL of LA in 5 mL increments, with gentle aspiration between injections. If the plexus is not visualized, place the needle tip in the plane between the posterior fascia of the SCM and the prevertebral fascia below. Inject 10 mL of LA as the needle is advanced, with intermittent aspiration. LA should be visualized spreading in the fascial plane.

●Anatomic technique – Draw a line from the mastoid process to the C6 transverse process (ie, the Chassaignac tubercle) along the posterior border of the SCM (figure 7). Insert the needle at the midpoint of this line. After negative aspiration, inject 10 to 15 mL of LA in 5 mL increments along the posterior border of the SCM, fanning the injection 2 to 3 cm above and below the needle insertion site, with gentle aspiration between injections. Injection deeper than 2 cm should be avoided to reduce injury to deep vessels and nerves.

Deep cervical plexus block technique — The deep cervical plexus block can be thought of as a cervical paravertebral block that targets the C2 to C4 spinal nerves. The patient is positioned supine, with the head slightly away from the side to be blocked.

●Ultrasound guidance – We suggest using ultrasound guidance for deep cervical plexus block to avoid neuraxial and vascular complications. The following technique is used [16]:

•Place a small, linear ultrasound probe in transverse orientation just below the mastoid process. Scan caudally in a line between the mastoid process and the C6 transverse process. Visualize the loop of the vertebral artery to avoid vascular puncture. The transverse process of C2 is approximately 1 cm caudal to the loop or in the vicinity of the artery and should be identified by a hyperechoic bony structure with a large, dark drop-off shadow deep to the bone.

•Insert the needle in plane (picture 2) to the transducer in an anterior-to-posterior orientation and advance until the tip contacts the superficial tip of the transverse process of the C2 vertebra. After negative aspiration, slowly inject 5 mL of LA. LA should be visualized spreading adjacent to the transverse process.

•Scan caudally to the transverse processes of C3 and C4, and repeat injections.

●Anatomic technique – Where ultrasound is unavailable, the following landmark-based approach can be used:

•Palpate the bony C6 transverse process (ie, the Chassaignac tubercle) at the level of the cricoid cartilage by applying digital pressure in a posteromedial direction. Draw a line from the mastoid process to the Chassaignac tubercle. Mark needle insertion sites for C2, C3, and C4 at 2 cm, 4 cm, and 6 cm caudal to the mastoid process, respectively. Insert the needle in a posteromedial and inferior orientation until the transverse process is contacted at 1 to 2 cm, at each level. After negative aspiration, slowly inject 3 to 5 mL of LA per level, with frequent aspiration. Avoid fanning and injection deeper than 2 cm.

Intermediate cervical plexus block technique — The intermediate cervical plexus block consists of a slightly more posterior superficial cervical block at C4. LA is deposited between the superficial and deep cervical fascia in the posterior triangle of the neck [17]. This block is performed using ultrasound guidance as follows:

●Place a small, linear ultrasound probe in transverse orientation in the posterior triangle of the neck at the level of the transverse process of C4. Insert the needle in plane to the transducer in an anterior-to-posterior orientation through the SCM and past the prevertebral fascia. The posterior cervical space is bounded by prevertebral fascia superficially, deep cervical paravertebral fascia medially, middle scalene or levator scapulae muscles posteriorly, and longus capitis or anterior scalene muscles anteriorly.

●After negative aspiration, inject 15 mL of LA in 5 mL increments, with gentle aspiration between injections. LA should be visualized spreading within the space described above.

Local anesthetic choice — A longer-acting, relatively dilute LA is preferred for most neck procedures (eg, 0.2% ropivacaine or 0.25% bupivacaine). Higher concentrations are not required because there is no need to block motor function (table 1) [14]. (See "Overview of peripheral nerve blocks", section on 'Drugs'.)

Complications — Complications are rare but are more common with deep cervical plexus blocks than with superficial blocks [11,13,14]. With deep block, potential complications include intravascular injection of LA into surrounding vessels, such as the carotid artery and external and internal jugular veins, but more commonly into the vertebral artery. Vertebral artery injection can cause immediate seizures even with injection of only a few mL of LA. Thus the LA should be injected very slowly and in small increments under ultrasound guidance. Other complications of this block include respiratory compromise with diaphragmatic or vocal cord paralysis, and, very rarely, intrathecal injection of LA.

A systematic review of complications of superficial and deep cervical plexus blocks reported that conversion to general anesthesia was more common with deep blocks (odds ratio [OR] 5.15) [13]. The most common reasons for conversion to general anesthesia were block failure and patient anxiety or lack of cooperation.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Local and regional anesthesia" and "Society guideline links: Local anesthetic systemic toxicity".)

SUMMARY AND RECOMMENDATIONS

●Scalp blocks

•Scalp nerve blocks can provide intraoperative and postoperative analgesia for craniotomy and for other procedures on the scalp and skull. They can also be used for treatment of chronic pain syndromes of the head and neck (figure 1). (See 'Applications of scalp blocks' above.)

•A total of 12 nerves (six on each side) are blocked to achieve a complete scalp block (figure 3). Complete scalp block includes blocks of the supraorbital, supratrochlear, auriculotemporal, zygomaticotemporal, greater occipital, and lesser occipital nerves. (See 'Scalp block technique' above.)

•Scalp blocks are performed using an anatomic technique, injecting 1 to 5 mL of long-acting local anesthetic (LA; eg, bupivacaine 0.25 or 0.5%, or ropivacaine 0.2 or 0.5%) using a 1.5-inch, 25- or 27-gauge needle (table 1). (See 'Scalp block technique' above.)

•The auriculotemporal nerve block can cause transient facial nerve paralysis, which can be avoided by minimizing the volume of LA injected and by using the technique described. (See 'Complications of scalp block' above.)

●Cervical plexus blocks

•Superficial and deep cervical plexus blocks anesthetize the anterior and lateral neck and scalp (figure 6). These blocks are particularly useful for awake carotic endarterectomy, in which neurologic monitoring of an awake patient may identify cerebral thromboembolic or ischemic events. They can also be used for postoperative analgesia for neck surgery. (See 'Cervical plexus blocks' above.)

•Superficial or intermediate cervical plexus block is usually preferred, rather than deep cervical plexus block, because the more superficial blocks are easier to perform, usually more effective, and are associated with less complications than deep cervical plexus block. (See 'Cervical plexus blocks' above.)

•We prefer using ultrasound guidance for superficial cervical plexus block, though an anatomic technique can be used as an alternative. (See 'Superficial cervical plexus block technique' above.)

•We suggest using ultrasound guidance rather than an anatomic technique for deep cervical plexus block (Grade 2C), to reduce the risk of complications. (See 'Deep cervical plexus block technique' above.)

•Cervical plexus blocks are performed with long-acting dilute LA (eg, 0.2% ropivacaine or 0.25% bupivacaine) (table 1). (See 'Local anesthetic choice' above.)

•Complications of cervical plexus block are rare, and include intravascular injection of LA, diaphragm or vocal cord paralysis, and very rarely, intrathecal injection of LA. (See 'Complications' above.)