Parotid Gland

Structure

The parotid gland is irregular in shape and consists of lobules of glandular tissue weighing approximately 25 g (Standring, 2016). The lobules are interspersed with adipose tissue and are covered in a layer of fascia, which forms the parotid capsule. This fascial layer derived from the deep cervical fascia of the neck.

Anatomical Relations

The parotid gland extends from the posterior border of the ramus of the mandible to the upper portion of the sternocleidomastoid muscle in the neck. It sits anteroinferior to the external acoustic meatus and lies over the master muscle and mastoid process.

The parotid gland contains, from deep to superficial, the external carotid artery, the retromandibular vein, and the facial nerve with its five main branches (temporal, zygomatic, buccal, marginal mandibular, and cervical).

Although the gland is largely superficial, a smaller deep portion sits deep to the mandibular ramus on the lateral aspect of the superior constrictor muscle. Therefore, a deep lobe tumor may not present as a facial swelling, but as a protrusion in the lateral oropharyngeal wall.

Function

The parotid gland secretes serous fluid upon parasympathetic stimulation. The influence of the sympathetic fibers is to reduce the secretions of the parotid gland.

Arterial Supply

Branches arising from the external carotid artery supply the parotid gland. These include parotid branches of the posterior auricular and superficial temporal arteries, and the transverse facial artery.

Venous Drainage

Venous drainage occurs via small unnamed branches draining into the external jugular vein.

Innervation

The lesser petrosal nerve is a visceral motor nerve that supplies parasympathetic innervation to the parotid gland. It carries preganglionic parasympathetic fibers to the otic ganglion. There, the lesser petrosal nerve synapses with the postganglionic parasympathetic fibers that travel with the auriculotemporal nerve to innervate the parotid gland. The auriculotemporal nerve also conveys general sensory information from the parotid gland.

Lymphatic Drainage

The parotid gland contains superficial and deep lymph nodes. Drainage of these nodes occurs through the deep lateral cervical nodes, primarily the internal jugular nodes either directly or via the infraauricular nodes. In 58% of cases, there is collateral drainage along lymph vessels that follow the course of the external jugular vein (Földi et al., 2012).

List of Clinical Correlates

- Parotitis

- Facial paralysis

- Acute sialadenitis

- Parotid duct obstruction

- Xerostomia

References

Földi, M., Földi, E., Strößenreuther, R. & Kubik, S. (2012) Földi's Textbook of Lymphology: for Physicians and Lymphedema TherapistsElsevier Health Sciences.

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41 edn.: Elsevier Limited.