Head and Neck Block Anatomy

Use of regional anesthesia for head and neck surgery declined rapidly after general anesthesia and tracheal intubation became available and accepted. One reason for the decline is that small doses of local anesthetic can easily produce systemic toxicity. Nevertheless, in few other areas in the body can such small doses of local anesthetic provide such effective regional block. There are still circumstances in which head and neck block is useful. Many of these involve the diagnosis or treatment of pain syndromes. Also, many plastic surgical procedures on superficial structures can be managed easily with effective block of the nerves of the head and neck. One crucial aspect of head and neck block for anesthesiologists is expertise in airway anatomy and innervation. In some circumstances in an anesthetic practice, proper airway management, including airway blocks, can be lifesaving.

Sensory innervation of the face is provided by the trigeminal nerve. Three branches of the trigeminal—the ophthalmic, maxillary, and mandibular—provide innervation, as illustrated in Figure 18-1. The cutaneous innervation of the posterior head and neck is from the cervical nerves. The dorsal ramus of the second cervical nerve ends in the greater occipital nerve, which provides cutaneous innervation to the larger portion of the posterior scalp (see Fig. 18-1). The greater occipital nerve is a continuation of the medial branch of the dorsal ramus of the second cervical nerve and ascends from the cervical vertebrae to the muscles of the neck in company with the occipital artery. The greater occipital nerve becomes subcutaneous in its course with the occipital artery immediately lateral to the inion, slightly inferior to the superior nuchal line (Fig. 18-2). The ventral rami of cervical nerves II, III, and IV provide the majority of cutaneous innervation to the anterior and lateral portions of the neck, with cervical nerve II providing innervation to the scalp through both the lesser occipital and the posterior auricular nerves (see Fig. 18-1). The superficial cervical plexus is formed as cervical nerves II, III, and IV leave the vertebral transverse processes and follow a course in which they become subcutaneous at the midpoint of the posterior border of the sternocleidomastoid muscle (see Fig. 18-2). At this point, the superficial cervical plexus can be easily blocked by infiltration.

Figure 18-1. Head and neck anatomy: innervation.

Figure 18-2. Head and neck anatomy: peripheral nerves.

The trigeminal nerve is a mixed motor and sensory nerve, although the majority of it involves sensory innervation. The only motor fibers are the branches that supply the muscles of mastication through the mandibular nerve. The trigeminal nerve is organized in the cranium within the trigeminal ganglion (gasserian or semilunar ganglion). From this ganglion, the ophthalmic nerve exits from the cranium through the superior orbital fissure, the maxillary nerve through the foramen rotundum, and the mandibular nerve through the foramen ovale (Fig. 18-3). After leaving these foramina, the maxillary and mandibular nerves follow courses that place them in the immediate proximity of the lateral pterygoid plate. The pterygoid plate is an important landmark for effective maxillary or mandibular block (Fig. 18-4). The terminal branches of the trigeminal nerve end in the supraorbital, infraorbital, and mental nerves. These exit through bony foramina that occur on a line perpendicular through the pupil, as illustrated in Figure 18-5.

Figure 18-3. Intracranial anatomy: trigeminal nerve and branches.

Figure 18-4. Coronal anatomy: peripterygoid relationships of maxillary and mandibular nerves.

Figure 18-5. Head and neck anatomy: superficial neural relationships.