Regional Anatomy of Superficial Cervical Plexus

The cervical plexus (CP) is formed from the first four cervical spinal nerves, C-1, C-2, C-3, and C-4. These spinal nerves emerge from the intervertebral foramina and pass behind the vertebral artery and vein in the gutter formed by the anterior and posterior tubercles of the corresponding transverse process of the cervical vertebrae (Fig. 1). As the nerves approach the lateral edge of the transverse process, all but C-1 divide into an ascending and descending branch. The nerve roots of C-2, C-3, and C-4 then enter a perineural space created by tendons and muscles that are attached to the anterior and posterior tubercles of the corresponding cervical vertebrae and form a fascial compartment. This compartment is lined anteriorly by the scalenus anterior muscle and posteriorly by the scalenus medius muscle. The ventral primary divisions of C-2, C-3, and C-4 separate into descending and ascending branches that form a pattern of three loops. These loops constitute the plexus formation, and they also communicate with sympathetic fibers derived from the superior, middle, and inferior cervical ganglia. In addition, there is an intricate fiber network that communicates with several cranial nerves. The vagus, hypoglossal, and accessory nerves all communicate with the cervical plexus. Such communication may partially explain some of the side effects often seen with CPB. Early in the formation of the CP, motor fibers course deep into the neck and separate from sensory fibers, which spread out superficially over the neck. This rare anatomical characteristic allows selective sensory blockade of the CP. The series of loops of the CP form the development of superficial and deep branches. The anterior branches course behind the anterior scalene muscle and then separate from the motor branches, continuing laterally to emerge superficially under the posterior border of the sternocleidomastoid muscle (Fig. 2). This anatomical separation enables the sensory branches of the CP, via the superficial cervical plexus (SCP) to be blocked selectively without any motor blockade within the neck.

Superficial cervical plexus branches and cutaneous innervation

Technique of superficial cervical plexus block

The four sensory nerves of the CP innervate the neck as follows

The lesser occipital nerve, with its origin predominately at C-2, emerges as the first of these sensory nerves. It ascends from the posterior border of the sternocleidomastoid muscle and supplies a band-like area behind the ear both superiorly and inferiorly.

The great auricular nerve, derived from C-2 and C-3, provides sensation to the skin over the parotid gland and posteriorly to the surface of the ear, as well as inferiorly to the angle of the mandible.

The third cutaneous nerve, which also arises from C-2 and C-3, is the transverse cervical or anterior cutaneous nerve, which passes anteriorly and perforates the platysma of the neck, where it divides into anterior and posterior branches. Sensory innervation from the mandible to the sternum and as far posteriorly as the angle of the mandible is supplied.

The supraclavicular nerve, which arises from C-3 and C-4, plies the largest surface area, because its branches penetrate the platysma and innervate inferiorly below the clavicle to the second rib and laterally over the deltoid area. The surface of the trapezius and acromion is also supplied by the branches of the supraclavicular nerve. All of these nerves make up the SCP and are easily blocked by infiltration with a local anesthetic.

Armamentarium.

22-Gauge, 4–5 cm, short bevel needle.

10–15 ml of local anesthetic.

Marker.

Preferably a monitor for vitals.