Introduction
The major salivary glands: parotid, submandibular, and sublingual glands, are paired and symmetric. In the oral cavity 700–900 minor salivary glands are found, the majority of which are located at the junction of the hard and soft palates. In this chapter, anatomic relations of the main salivary glands are shown in a layered fashion.
Parotid Gland
Location
The face ( Fig. 1.1 ) is divided into two main compartments: the superficial compartments dedicated to mimicry and innervated by the facial nerve; and the deep visceral compartment innervated by the other cranial nerves. The superficial compartments are constituted by five layers: (1) skin; (2) subcutaneous tissue including fat and tela-retinaculum cutis ( Fig. 1.2 ); (3) submuscular aponeurotic system (SMAS) ( Fig. 1.3 ); (4) deep facial space; (5) deep facial fascia. The parotid gland is in the visceral compartment ( Fig. 1.4 ), under the deep facial fascia, i.e., deep to the 5th superficial compartment layer.
It lies within a deep hollow, known as the parotid region. The parotid region is bounded by the: superiorly–zygomatic arch; anteriorly–masseter muscle and mandible bone ( Fig. 1.5 ); posteriorly–external ear tragal cartilage and sternocleidomastoid muscle; inferiorly, the inferior parotid pole is between the ramus of the mandible and sternocleidomastoid muscle overlying the digastric muscle ( Fig. 1.5 ). The deep aspect rests in the prestyloid compartment of the parapharyngeal space ( Fig. 1.6 ).
Description
Shape
The parotid gland is a bilateral prismatic structure that looks like an inverted three-sided pyramid, which displays a lobular and irregular morphology ( Fig. 1.1 ). It presents at four surfaces: superior, superficial, anteromedial, and posteromedial; separated by three borders: anterior, posterior, and medial.
Constitution
Anatomically, the parotid can be divided into deep and superficial lobes, which are separated by the facial nerve. Approximately 80% of the parenchyma is located as superficial lobe.
Vascularization and Innervation
Vasculature
Blood is supplied by the posterior auricular and superficial temporal arteries. They are both branches of the external carotid artery, which arise within the parotid gland ( Figs. 1.7 , 1.8 ).
Venous drainage is achieved via the retromandibular vein. It is formed by unification of the superficial temporal and maxillary veins ( Figs. 1.7 , 1.8 ).
Innervation
The parotid gland receives sensory and autonomic innervation. The autonomic innervation controls the rate of saliva production. Sensory innervation is supplied by the auriculotemporal nerve (gland) and the great auricular nerve. The parasympathetic innervation to the parotid gland has a complex path. It begins with the glossopharyngeal nerve (cranial nerve IX). This nerve synapses with the otic ganglion (a collection of neuronal cell bodies). The auriculotemporal nerve then carries parasympathetic fibers from the otic ganglion to the parotid gland. Parasympathetic stimulation causes an increase in saliva production.
Sympathetic innervation originates from the superior cervical ganglion, part of the paravertebral chain. Fibers from this ganglion travel along the external carotid artery to reach the parotid gland. Increased activity of the sympathetic nervous system inhibits saliva secretion, via vasoconstriction.
Anatomic Relationships
The Parotid Bed
The gland is embedded in its capsule and the parotid-masseteric fascia (layer 5), which attaches to the root of the zygoma and continues as a thin fascia that can be separated from tragal and conchal cartilage by blunt dissection. A thick fascia is attached to the periosteum of the mastoid process and tympano-mastoid suture, the so-called Loré’s fascia. A thick fascia at the antero–inferior tip of the parotid separates it from the submandibular gland. Anteriorly, this parotid-masseteric fascia extends to the buccinator aponeurosis, embedding Stensen’s duct until its penetration through the buccinator muscle ( Fig. 1.4 ).
The Facial Nerve (Cranial Nerve VII)
The extratemporal segment exits the skull base through the stylomastoid foramen posterolateral to the styloid process and anteromedial to the mastoid process. The facial nerve as it enters the parotid forms the pes anserinus ( Figs. 1.7–1.10 ). The upper divisions include the temporal–facial branches and the lower divisions include the cervico-facial branches. These branches innervate the muscles of facial expression.
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