Chapter 8 Systemic Anatomy of the Head and Neck
The arteries that ultimately supply the head and neck originate from the subclavian and common carotid arteries. On the right side, the common carotid and subclavian arteries originate from the brachiocephalic artery just posterior to the right sternoclavicular joint in the root of the neck. On the left side, the common carotid and subclavian arteries originate separately from the arch of the aorta within the superior mediastinum.
The arteries of the head and neck are illustrated in Figure 8-1 and listed in Table 8-1. Regional detailed descriptions of the arteries are found in Chapter 7.
The venous drainage of the head and neck may be conveniently grouped into a set of external or superficial veins and a set of deep or intracranial veins. The superficial veins drain to either the external jugular vein or the internal jugular vein; the deep veins drain to the internal jugular vein.
The external jugular vein picks up tributaries from posterior superficial structures of the head and face and descends along the sternocleidomastoid muscle. Inferiorly, it enters the posterior triangle and joins the subclavian vein.
The internal jugular vein drains intracranial structures, leaves the skull through the jugular foramen, and descends in the neck within the carotid sheath. At the root of the neck, it joins the subclavian vein to form the large brachiocephalic vein. In the superior mediastinum the right and left brachiocephalic veins unite to form the superior vena cava, which, in turn, drains to the right atrium of the heart.
Knowledge of the routes by which lymph flows from the head and neck back to the venous system is essential to understand lymphatic spread of infections and cancer (Table 8-3). For a general discussion of the lymphatic system, see Chapter 1, Section 6.
|Lymph Node||Structures Drained (Afferents)||Efferents|
|Superficial Horizontal Ring|
|Submental||Lower lip, chin, tip of tongue, anterior floor of mouth||Submandibular nodes, jugulo-omohyoid nodes|
|Submandibular||Submental nodes, cheek, nose, upper lip, maxillary teeth, vestibular gingivae, mucosa and gingivae of the hard palate, posterior floor of mouth, lateral aspects of anterior two thirds of tongue||Nodes of deep cervical chain|
|Superficial||Eyelids, temples, prominence of the cheek, auricle||Deep parotid nodes, deep cervical nodes|
|Deep||Middle ear, external auditory meatus, soft palate, posterior aspect of nasal cavity, superficial parotid nodes||Deep cervical nodes|
|Mastoid (retroauricular)||Scalp, auricle||Deep cervical nodes|
|Occipital||Posterior scalp||Deep cervical nodes|
|Deep Horizontal Ring|
|Retropharyngeal||Posterior nasal cavity, nasopharynx, soft palate, middle ear, external auditory meatus||Deep cervical nodes|
|Paratracheal, pretracheal, prelaryngeal, and infrahyoid||Larynx, trachea, pharynx, esophagus||Deep cervical nodes|
|Deep Cervical Vertical Chain|
|Jugulodigastric, jugulo-omohyoid, and other nodes of the cervical chain||Entire chain receives afferents from the superficial horizontal ring of nodes and the deep horizontal ring of nodes||Left side: joins thoracic duct at junction of left subclavian and internal jugular veinsRight side: joins right subclavian and right bronchomediastinal lymph trunks to enter junction of right subclavian and right internal jugular veins|
The lymphatics of the head and neck, as in other areas of the body, drain toward groups of lymph nodes. The nodes act as filters and add lymphocytes to the lymph fluid. In the head and neck, the lymph nodes may be conveniently grouped into (1) a horizontal ring of superficial nodes, (2) a horizontal ring of deep nodes, and (3) two vertical chains of deep cervical nodes. Both horizontal rings drain to the two deep vertical chains (Figure 8-4).
The superficial ring surrounds the transition area of neck to head and is arranged into five main groups (Figure 8-5; see Table 8-3). These nodes are palpable when infected.
The submandibular nodes lie within the submandibular region, scattered over the surface of the submandibular salivary gland and in the interval between the salivary gland and the medial surface of the mandible. An extension of the submandibular group overlies the cheek superiorly as the buccal group of nodes.
The submandibular nodes receive afferent vessels from the (1) submental nodes; (2) cheek, nose, and upper lip of the face; (3) maxillary teeth; (4) vestibular gingivae; (5) mucosa and gingivae of the hard palate; (6) posterior floor of the mouth; and (7) tongue.
The deep parotid nodes receive lymph drainage from (1) the middle ear and external auditory meatus, (2) the soft palate, (3) the posterior aspect of the nasal cavity, and (4) the superficial parotid nodes.
The deep cervical chains descend from the base of the skull down to the root of the neck, and they parallel the courses of the right and left internal jugular veins. The deep cervical chain receives afferent drainage from the nodes of the superficial ring and the deeper visceral ring of lymph nodes. As the deep cervical chains approach their terminations, they form the right and left jugular lymph trunks.
On the left side, the jugular trunk joins the thoracic duct or enters the junction of the subclavian vein and internal jugular vein independently. On the right side, the right jugular, subclavian, and bronchomediastinal lymph trunks may join to form a common right lymphatic duct, which, in turn, empties to the confluence of the right subclavian and internal jugular veins. Alternatively, the right jugular trunk may independently enter the venous system at the same point.
Mandibular lingual gingivae and the mucosa of the floor of the mouth drain to the submandibular nodes or directly to the deep cervical chain. The anterior segment drains initially to the submental nodes.
The tip of the tongue drains to the submental lymph nodes, the lateral aspects of the anterior two thirds drain to the submandibular nodes, and the medial portion of the anterior two thirds drain directly to the deep cervical nodes (Figure 8-6).
The anterior portion of the nasal cavity drains to the submandibular nodes. The posterior nasal cavity, sinuses, and nasopharynx drain directly to the deep cervical chain or indirectly via the deep parotid nodes or the retropharyngeal nodes.
The lymphatics of the larynx above the vocal cords drain initially to the infrahyoid nodes or directly to the deep cervical chain. The laryngeal lymphatic vessels below the vocal cords drain to the prelaryngeal and pretracheal nodes or directly to the deep cervical chain.
A general description of the nervous system is found in Chapter 1, Section 7, and a description of the brain and attached cranial nerves is presented in Chapter 7, Section 2. In addition, a description of each cranial nerve is given as it appears in the various regions of the head. A summary of the cranial nerves is presented in Table 8-4.
Twelve pairs of cranial nerves arise from the brain. The first two nerves are remote from the brain and communicate with the brain via long extensions, or tracts. The remaining ten nerves arise directly from the brainstem.
Cranial nerves may perform one or more functions; possible functional components include (1) somatic afferent (general sensory from body structures), (2) visceral afferent (visceroceptive from glands and viscera), (3) special afferent (special sensory smell, sight, taste, hearing, and balance), (4) somatic efferent (motor to muscles derived from somites), (5) branchial efferent (motor to muscles derived from branchial arches), and (6) visceral efferent (autonomic motor to smooth muscle and glands).
The special sensation of smell is the only functional component of the olfactory nerve (Figure 8-7). The olfactory nerve originates from bipolar olfactory cells within the nasal mucosa, where peripheral processes end as specialized smell receptors in the mucosa covering the superior concha and upper nasal septum. Central processes collect as 18 to 20 branches of the olfactory nerve proper. These pass upward through the cribriform plate to the anterior cranial fossa and enter the overlying olfactory bulbs. Here they synapse with mitral cells, and their central processes pass back along the olfactory tract to the olfactory area of the forebrain.
Functional Component. The special sensation of sight is the sole functional component of this cranial nerve (Figure 8-8). Classically (but incorrectly) the optic nerve is described as the section that passes posteriorly from the eyeball to the optic chiasma. Actually, the optic nerve proper is contained within the retina of the eye and originates from rod cells (nondiscriminating sight) and cone cells (discriminating sight and color). These receptor cells occupy the most external portion of the retina and receive incoming light. Central processes pass inward to synapse with bipolar cells, which, in turn, synapse with ganglionic cells of the innermost layer. Central processes of the ganglionic cells collect and leave the eyeball as the optic nerve. The nerve, or tract, leaves the orbit through the optic canal, and right and left nerves join at the optic chiasma. Here the fibers originating from the medial (nasal) half of the retina decussate; the fibers of the lateral (temporal) half of the retina do not decussate. The optic tract continues posteriorly from the chiasma, and this ends in the lateral geniculate body of the thalamus, where the optic fibers synapse. Postsynaptic fibers pass posteriorly through optic radiations to the visual cortex in the occipital lobe of the cerebral hemispheres.
The oculomotor nerve arises from the interpeduncular fossa of the midbrain and passes forward to enter and traverse the cavernous sinus (Figure 8-9). The oculomotor nerve then enters the orbit through the superior orbital fissure.
Lesions of the oculomotor nerve may reveal one or more of the following: (1) drooping of the upper lid (ptosis); (2) inability to move the eye upward, downward, and medially; (3) lack of pupil constriction when challenged with a light; and (4) inability to accommodate the eye for close vision.
The trochlear nerve arises as a slender thread from the dorsal aspect of the midbrain and sweeps anteriorly under the cover of the free edge of the tentorium cerebelli (Figure 8-10). It pierces the dura of the triangular field, enters and traverses the cavernous sinus, and enters the orbit through the superior orbital fissure.