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Head and Neck Anatomy and Embryology with Radiology Correlates


Key Points

  • 1.

    The six branchial arches form the skeletal and muscular derivatives of the head and neck and the six pharyngeal pouches form the endothelium and glands. Each arch is associated with a nerve and artery.

  • 2.

    Aberrant embryologic development can cause first, second, third, and fourth branchial cleft anomalies. Branchial cleft anomalies have associated sinus tracts, which pass deep to their associated aortic arch derivatives.

  • 3.

    Cervical lymphadenectomy (neck dissection) is based on lymphatic drainage patterns to regional lymph nodes delineated by sublevels of the neck.

  • 4.

    The upper aerodigestive tract is divided into the nasal cavity, oral cavity, nasopharynx, oropharynx, hypopharynx, and larynx.

  • 5.

    Deep neck space infections can travel through the neck and into adjacent regions via the retropharyngeal, danger, and prevertebral spaces.

Pearls

  • 1.

    The second branchial cleft is the most common branchial cleft to develop an anomaly.

  • 2.

    The soft palate divides the nasopharynx from the oropharynx, and the hyoid bone separates the oropharynx from the hypopharynx.

  • 3.

    The parapharyngeal space has two compartments: pre-styloid and post-styloid, with different contents.

  • 4.

    The retropharyngeal space extends from the skull base to the mediastinum, the danger space extends from the skull base to the diaphragm, and the prevertebral space extends from the clivus to the coccyx.

  • 5.

    The lymphatics in the neck are subdivided into seven different levels with boundaries formed by anatomic landmarks.

Questions

1

What are the skeletal derivatives of the six branchial arches?

See Table 10.1 . The first and second arches have cartilaginous precursors: Meckel’s and Reichert’s, respectively.

Table 10.1
BRANCHIAL ARCH SKELETAL DERIVATIVES MUSCLE DERIVATIVES CRANIAL NERVES (CN) AORTIC ARCH ARTERY
First Meckel’s cartilage: Proximal – Body and ramus of the mandible, sphenomandibular ligament, anterior malleolar ligament, malleus (except for the manubrium), and incus (except for the long process). Distal – Withers; the body of the mandible is formed from intramembranous growth.
Maxillary process forms the premaxilla, maxilla, zygoma and part of the temporal bone.		 Muscles of mastication: temporalis, masseter, and medial and lateral pterygoid muscles.
Tensor tympani, tensor veli palatini, anterior belly of the digastric, and mylohyoid muscles.		 Trigeminal nerve (CN V) Maxillary artery
Second Reichert’s cartilage: Proximal – Styloid process, manubrium of the malleus, long process of the incus, and stapes superstructure. Central – Withers and forms a band, the stylohyoid ligament. Distal – Superior body and lesser cornu of the hyoid bone. Muscles of facial expression and posterior belly of the digastric, stylohyoid, and stapedius muscles. Facial nerve (CN VII) Stapedial artery (degenerates)
Third Inferior body and greater cornu of the hyoid bone Stylopharyngeus muscle Glossopharyngeal nerve (CN IX) Common and internal carotid arteries
Fourth Thyroid, cricoid, arytenoid, corniculate, and cuneiform laryngeal cartilages Pharyngeal muscles (superior, middle, and inferior constrictor muscles), striated muscle of the upper half of the esophagus, and extrinsic and intrinsic muscles of the larynx. Vagus nerve (CN X) Aorta (left); proximal subclavian artery (right)
Sixth Thyroid, cricoid, arytenoid, corniculate, and cuneiform laryngeal cartilages Pharyngeal muscles (superior, middle, and inferior constrictor muscles), striated muscle of the upper half of the esophagus, and extrinsic and intrinsic muscles of the larynx. Vagus nerve (CN X) Ductus arteriosus and pulmonary artery (left); pulmonary artery (right)

2

What are the muscular derivatives of the six branchial arches?

See Table 10.1 .

3

What do the six pharyngeal pouches form?

See Table 10.2 . The pharyngeal pouches are composed of endoderm and form glandular structures.

Table 10.2
PHARYNGEAL POUCH POUCH DERIVATIVES
First Inner layer of the tympanic membrane, middle ear mucosa, and eustachian tube
Second Epithelial lining of the palatine tonsil
Third Superior forms the inferior parathyroid glands and inferior forms the thymus
Fourth Superior parathyroid glands
Fifth, sixth Parafollicular (C) cells

4

What cranial nerve innervates the derivatives of each branchial arch?

See Table 10.1 . The cranial nerve associated with each branchial arch innervates the muscles formed by the same branchial arch.

5

List the aortic arch artery associated with each branchial arch.

See Table 10.1 .

6

Describe the potential tracts of the branchial cleft sinuses.

Sinus tracts typically have a pattern of passing deep to the associated aortic arch derivatives. It is important to attempt surgical excision of both the sinus tract along as well as the branchial cleft cyst to prevent recurrence.

First branchial cleft anomalies are duplications of the membranous part of the external auditory canal and are divided into two types. Type I is of ectodermal origin and is a duplication anomaly of the external auditory canal located antero-inferior to the lobule. Type II is of ectodermal and mesodermal origin, duplicates the cartilage in addition to the external auditory canal, and presents below the angle of the mandible. First branchial cleft tracts may pass medial or lateral to the main trunk of the facial nerve or between branches.

Second branchial cleft anomalies present below the angle of the mandible, at the anterior border of the sternocleidomastoid muscle (SCM). The tract passes deep to the external carotid artery, stylohyoid, and digastric muscle and superficial to the internal carotid artery, opening in the tonsillar fossa.

Third branchial cleft anomalies present anterior to the SCM and lower in the neck than second branchial cleft anomalies. The tract passes deep to the glossopharyngeal nerve and the internal carotid artery and superficial to the vagus nerve, opening in the pharynx at the thyrohyoid membrane or piriform sinus.

Fourth branchial cleft anomalies are predominantly left-sided, presenting as thyroid masses or paratracheal masses in the lateral neck. The tract of this sinus passes deep to the superior laryngeal nerve and superficial to the recurrent laryngeal nerve opening into the hypopharynx.

7

What is the most common branchial cleft anomaly?

Second branchial cleft anomalies are the most common (approximately 95% of all anomalies). First branchial cleft anomalies are the second most common. Third and fourth branchial cleft anomalies are rare.

8

What are the boundaries and subsites of the oral cavity?

  • Anterior: Vermillion border of the lip

  • Superior: Hard–soft palate junction

  • Lateral: Tonsillar pillars

  • Posterior/inferior: Circumvallate papillae of the tongue

  • Subsites: Lip, oral tongue (anterior two-thirds), buccal mucosa, floor of mouth, hard palate, upper and lower gingiva (alveolar ridges), and retromolar trigone

9

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