Parotid gland

Glandula parotidea

Also known as: parotid

The parotid is the largest salivary gland and is purely serous. It lies in front of the ear and wraps around the ramus of the mandible. The facial nerve, the retromandibular vein and the external carotid artery all pass through it.

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Overview

Mass≈15–30 g

Duct length≈5 cm

Duct openingOpposite the maxillary 2nd molar

The gland is wedge-shaped and fills the retromandibular fossa. It extends from the zygomatic arch down to the angle of the mandible and from the masseter back to the mastoid process and sternocleidomastoid. It is enclosed in a tough parotid sheath derived from the investing layer of deep cervical fascia, so inflammatory swelling is tense and very painful.

The facial nerve (VII) enters the gland after leaving the stylomastoid foramen and divides into its five terminal branches within it. The nerve plexus is a surgical plane that separates "superficial" and "deep" parts of the gland. From superficial to deep, the structures inside the gland are the facial nerve branches, the retromandibular vein and the external carotid artery, which divides here into the maxillary and superficial temporal arteries. Intraparotid lymph nodes also lie within it.

The parotid (Stensen) duct, about 5 cm long, runs forward across the masseter about a fingerbreadth below the zygomatic arch. At the anterior border of masseter it turns medially, pierces the buccinator, and opens into the vestibule on the parotid papilla opposite the maxillary second molar.

Location: Lateral face, in front of and below the external ear, overlying the ramus of the mandible and the masseter.

Parts & subdivisions

Superficial and deep parts
Surgical "lobes" separated by the plane of the facial nerve plexus. A superficial parotidectomy removes tissue lateral to the nerve.
Parotid duct (Stensen)
About 5 cm long. Crosses the masseter, pierces the buccinator and opens opposite the upper second molar.
Facial nerve within the gland
Divides into temporal, zygomatic, buccal, marginal mandibular and cervical branches. It is motor to the muscles of facial expression only and does not supply the gland.
Accessory parotid gland
Small, inconstant detached lobule lying on the duct over the masseter.

Anatomy

Innervation: Parasympathetic secretomotor pathway: inferior salivatory nucleus → glossopharyngeal nerve (IX) → tympanic nerve (Jacobson) → tympanic plexus → lesser petrosal nerve → otic ganglion (synapse) → postganglionic fibres travel on the auriculotemporal nerve (V3) to the gland. Sympathetic fibres come from the superior cervical ganglion via the external carotid plexus. Sensory: auriculotemporal nerve for the gland; great auricular nerve (C2–C3) for the sheath and overlying skin.
Arterial supply: Branches of the external carotid artery within the gland: posterior auricular, superficial temporal and transverse facial arteries.
Venous drainage: Retromandibular vein.
Lymphatic drainage: Superficial and deep parotid nodes, draining to the deep cervical nodes.
Relations: Superficial: skin, fascia, great auricular nerve and parotid nodes. Deep: styloid process and its muscles, the internal carotid artery and internal jugular vein (separated by the styloid apparatus), and the posterior belly of digastric. Anterior: masseter and mandibular ramus. Posterior: mastoid process and sternocleidomastoid.
Histology: Purely serous acini with basophilic basal cytoplasm and apical zymogen granules. There are prominent striated ducts, and adipocytes become more numerous with age.

Function

Secretes serous, amylase-rich saliva, about 25% of resting and about 50% of stimulated flow.

Secretions: Watery serous saliva rich in α-amylase, proline-rich proteins and bicarbonate. It contains little mucin.

Clinical significance

Mumps (epidemic parotitis)

A paramyxovirus infection that causes painful, usually bilateral parotid swelling which lifts the ear lobe. Complications include orchitis, pancreatitis, meningitis and sensorineural deafness. MMR vaccination prevents it.

Parotid tumours and the facial nerve

Pleomorphic adenoma is the commonest salivary tumour. Facial nerve weakness with a parotid mass strongly suggests malignancy. Surgery must identify and preserve the facial nerve trunk.

Frey syndrome

After parotidectomy, cut parasympathetic auriculotemporal fibres can regrow into sweat glands of the overlying skin. The cheek then sweats and flushes during eating ("gustatory sweating").

Mnemonics

Facial nerve branches

"To Zanzibar By Motor Car": Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical.

Test yourself

Postganglionic parasympathetic secretomotor fibres to the parotid gland come from which ganglion?

Submandibular ganglion
Pterygopalatine ganglion
Ciliary ganglion
Otic ganglion

Answer: Otic ganglion

The pathway is IX → tympanic nerve → lesser petrosal nerve → otic ganglion → auriculotemporal nerve (V3) → parotid. The submandibular ganglion (fibres from VII via the chorda tympani) supplies the submandibular and sublingual glands.

The parotid (Stensen) duct opens into the oral vestibule opposite which tooth?

Maxillary second molar
Mandibular second molar
Maxillary first premolar
Mandibular central incisor

Answer: Maxillary second molar

The duct crosses the masseter, pierces the buccinator and opens on the parotid papilla opposite the upper second molar. The submandibular duct opens at the sublingual caruncle beside the lingual frenulum.