Chapter 35: Neck Anatomy

Neck Anatomy anatomical overview of the neck, Chapter 35, thoroughly examines its structures, starting with the base of the cranium and inferior border of the mandible down to the thoracic inlet, emphasizing surface landmarks and surgical considerations such as relaxed skin tension lines to minimize postoperative scarring. The region is fundamentally organized by the prominent sternocleidomastoid muscle, which divides the quadrilateral area into the anterior and posterior triangles, each further subdivided into clinical zones like the carotid, digastric, occipital, and supraclavicular areas. Key skeletal features include the U-shaped hyoid bone, developed from the second and third pharyngeal arches, which serves as a crucial anchor for the suprahyoid and infrahyoid strap muscles, such as the sternohyoid and omohyoid, with the thyrohyoid muscle having a unique innervation deriving fibers from the first cervical spinal nerve. A major focus is the multilayered deep cervical fascia—including the investing, visceral, and prevertebral/alar layers—which create defined tissue compartments like the pretracheal space and the highly significant danger space, whose loose connective tissue offers a potential route for rapid, downward spread of infection toward the mediastinum. The neurovascular system features the common carotid artery, which often bifurcates near the upper border of the thyroid cartilage and contains the baroreceptive carotid sinus and chemoreceptive carotid body. The external carotid artery supplies the neck and face via branches including the superior thyroid, lingual, facial, and occipital arteries, while the internal carotid artery is typically branchless in the neck. Innervation stems from the cervical plexus, which gives rise to cutaneous nerves, the ansa cervicalis (supplying most strap muscles), and the critical phrenic nerve, which descends across the anterior surface of the scalenus anterior muscle. Crucial cranial nerves traversing this area are the Vagus nerve (X), supplying the larynx via the superior and recurrent laryngeal nerves (which must be protected during surgery), and the Accessory nerve (XI), which provides the sole motor supply to the sternocleidomastoid and the primary motor supply to the trapezius. The visceral compartment contains the trachea and cervical oesophagus, as well as the thyroid gland, which is intensely vascular and produces T3 and T4 hormones, and the small, paired parathyroid glands, essential for calcium regulation through parathyroid hormone (PTH), requiring meticulous preservation during thyroid surgery within surgical reference points like Beahr’s triangle. Lymphatic drainage is hierarchically managed through defined levels (I through V and central levels VI/VII), which guide selective neck dissections for metastatic disease.