1 Neck Anatomy

Jeremie O. Piña and Sumner A. Slavin

1.1 Key Points

• Knowledge of neck anatomy empowers the clinician to optimize patient-specific outcomes in surgical and nonsurgical neck rejuvenation.

• Maintaining the integrity of the key supporting structures within the neck (e.g., superficial fascial layer) helps curtail bleeding from cut muscle and preserves the strength of the musculofascial layer during neck dissection.

• It is critical to know where to find the neurovascular structures most at risk during neck rejuvenation procedures, and to understand how to effectively treat any related complications.

1.2 Cervical Triangles

Although clinicians typically approach the neck in terms of aesthetic units, anatomists still refer to the muscular triangles when describing both the surfaces and contents of the neck. The sternocleidomastoid muscle divides the sides of the neck into the anterior and posterior triangles.

The anterior triangle is bordered by the midline and the mandible, further subdividing into the submandibular, carotid, and muscular triangles. The carotid and muscular triangles are separated by the posterior belly of the digastric muscle (accompanied by the stylohyoid muscle), and the region splitting the anterior bellies of the digastric muscles from the hyoid bone is referred to as the submental triangle. ▶ [1]

The posterior triangle is bounded by the trapezius, sternocleidomastoid, and middle third of the clavicle. This triangle can be further subdivided as well, into the supraclavicular (omoclavicular) and posterior cervical (occipital) triangles, split by the inferior belly of the omohyoid muscle. ▶ [2]

1.3 Fasciae of the Neck

1.3.1 Superficial

As a discrete sheet of subcutaneous connective tissue, the superficial fascia encases the platysma muscle (the only muscle in the head and neck without a direct bony origin or insertion) and fuses into a single layer along the neck midline, forming a midline bridge of superficial fascia so thin that in most patients it is essentially invisible. ▶ [3] During subcutaneous lipectomy in the neck, maintaining the integrity of this thin superficial fascial layer helps curtail bleeding from cut muscle and preserves the strength of the musculofascial layer.

The superficial fascia arises inferiorly from the deep thoracic fascia, covering the pectoralis major and deltoid muscles. At the lateral aspects of the neck, the superficial fascia fuses with the investing deep fascia covering the sternomastoid and trapezius muscles. Above the mandibular border, the superficial fascia (then referred to as the superficial musculoaponeurotic system, or SMAS) and its platysma component become increasingly fibrous. While there is always a distinction between the SMAS and deep fascia (also called the parotideomasseteric fascia or parotid capsule) at the lateral aspect of the cheek, the pretragal region represents a region of closely attached fibers. ▶ [4] Lateral to the parotid, however, the SMAS becomes thinner and increasingly difficult to visualize (gross and microscopically). It eventually becomes an invisible epimysium, enveloping the superficial layer of the perioral and periorbital muscles (e.g., risorius, zygomaticus major and minor, orbicularis oculi). Further toward the facial midline, the SMAS may continue across the nasolabial crease as the superficial portion of the orbicularis oris muscle. ▶ [5]

Superior to the parotid gland, the SMAS and deep fascia of the cheek coalesce approximately 1 cm caudal to its insertion into the zygomatic arch, signifying that the SMAS is likely not contiguous with the superficial fascia of the lateral orbital and temporal regions of the scalp (this may be referred to as the superficial temporalis fascia, the temporoparietal fascia, the galea aponeurotica, or the fronto-occipitalis layer). ▶ [6] However, there remains some scrutiny in the field regarding this anatomical convergence. ▶ [7]

1.3.2 Deep

The deep fasciae of the neck are arranged somewhat concentrically, running contiguous on the inferior aspect with the deep thoracic fascia and on the superior aspect with the cranial fasciae. The most superficial layer of the deep fascia (and the most important in regard to neck lift surgery) is the investing deep fascia (often confused with the real superficial fascia of the neck, aka the platysma and SMAS). ▶ [7] This superficial layer of the deep cervical fascia envelops the deep neck tissues from anterior to posterior in a continuous sleeve of connective tissue, similar to the fasciae seen encompassed in the limbs.

Further division of the deep investing fascia encloses the sternomastoid and trapezius muscles before reconverging into a single sheet covering the anterior and posterior triangles of the neck. The deep investing fascia maintains attachments to all exposed bony parts and ligaments in its path, from the occipital protuberance, ligamentum nuchae, and spine of C7 posteriorly to the superior nuchal line, mastoid process, and mandible cephalically. ▶ [8] It splits above the mandible to encapsulate the parotid gland, and splits below the mandible to envelop the submandibular salivary gland. A thickening of this fascia extends from the tip of the styloid process to the angle of the mandible (aka the stylomandibular ligament or interglandular septum), creating a common wall between the capsules surrounding the parotid and submandibular glands. ▶ [9]

1.3.3 Infrahyoid Muscle Fascia

Classically referred to as the “middle fascia,” the fascia of the infrahyoid muscles actually consists of two distinct layers: the superficial layer (enclosing the sternohyoid and omohyoid muscles) and the deep layer (investing the sternothyroid and thyrohyoid muscles). ▶ [10]

1.3.4 Visceral Fascia

The visceral fascia is split into two components: the pretracheal fascia (covering the larynx, trachea, and thyroid gland) and the buccopharyngeal fascia (covering the buccinator muscle and dorsal esophagus).

1.3.5 Prevertebral Fascia

The prevertebral fascia envelops the vertebral column and its surrounding muscles as well as covering the prevertebral musculature, forming the floor of the posterior triangle of the neck (aka the “fascial carpet”).

1.3.6 Carotid Sheath

The carotid sheath envelops the internal and common carotid arteries, as well as the jugular vein and the vagus nerve. The pretracheal (thyroid) fascia is adherent to it along with the investing deep fascia under the sternomastoid muscle. ▶ [11] Along the lateral aspect of the sternomastoid muscle, the nerves providing sensory input to the neck (e.g., great auricular nerve, lesser occipital nerve, transverse cervical nerve, and supraclavicular nerves) pierce the investing deep fascia and thereafter become enclosed by the thin layer of superficial neck fascia. ▶ [12] Further posterior along the edge of the sternomastoid muscle, the spinal accessory nerve emerges within the posterior triangle of the neck, continuing downward and backward toward the trapezius muscle under a thin two-layer veil of fascia (investing deep and superficial neck fasciae).

Anterior to the sternomastoid muscles, the investing deep fascia crosses the midline of the neck, enveloping and attaching to the entire body and the greater horn of the hyoid bone, finally inserting above into the symphysis menti. The fascia of the anterior bellies of the digastric muscles and the fascia of the mylohyoid muscles are also contained within this investing deep fascia. Of particular importance in neck lift surgery, the investing deep fascia often needs to be vertically lengthened by partial transverse incisions or excisions to improve the depth and definition of the hyoid angle. ▶ [10]

When operating on the subplatysmal midline and paramedian areas, the investing deep fascia acts as a visual and mechanical safety barrier, given that there are no vital midline structures superficial to the investing deep fascia. ▶ [4] Inferior to the hyoid bone, along the midline of the neck between the infrahyoid strap muscles, exist three layers of fascia: the investing deep fascia, the fused strap muscle fascia, and the pretracheal fascia. Clinically, all three of these fascial layers appear as one blended matrix. ▶ [13]

1.4 Platysma and Lower Lip

Situated between the...