Structure and relations
The parotid gland fills the space between the ramus of the mandible in front and the mastoid process and sternocleidomastoid behind, below the external acoustic meatus. It is roughly wedge-shaped, with a superficial surface under the skin and a deep part that reaches in towards the styloid process and the parapharyngeal space.
The investing layer of deep cervical fascia splits to form a dense capsule around it. Swelling inside this tight capsule explains the pain of mumps and parotitis.
- Superficially: skin, superficial fascia, branches of the great auricular nerve and the superficial parotid nodes.
- Anteromedially: masseter, the ramus of the mandible and medial pterygoid.
- Posteromedially: the mastoid process, sternocleidomastoid, the posterior belly of digastric and the styloid process with its muscles.
- Above: the external acoustic meatus and the temporomandibular joint.
The facial nerve runs through the gland and separates a larger superficial part from a smaller deep part. This division is surgical, not a true anatomical lobe.
Parotid duct and accessory gland
The parotid (Stensen's) duct is about 5 cm long and carries saliva from the anterior border of the gland into the mouth. It crosses masseter about a finger's breadth below the zygomatic arch, turns sharply medially at the front edge of masseter, pierces the buccal fat pad and buccinator, and opens on a small papilla in the cheek opposite the upper second molar tooth.
Its surface marking is the middle third of a line from the lower border of the tragus to a point midway between the ala of the nose and the red margin of the upper lip. The duct can be rolled against the tensed masseter.
The accessory parotid gland is a small detached lobule lying on masseter above the duct, between it and the zygomatic arch. Its own small ducts drain into the main duct. Buccal branches of the facial nerve and the transverse facial artery run close to the duct across masseter.
Structures within the gland
Three main structures pass through the parotid, arranged from superficial to deep.
- Facial nerve (CN VII): the most superficial. It enters the posteromedial surface after leaving the stylomastoid foramen and giving the posterior auricular nerve and branches to the posterior belly of digastric and stylohyoid.
- Retromandibular vein: formed in the gland by the superficial temporal and maxillary veins.
- External carotid artery: the deepest. It divides behind the neck of the mandible into the superficial temporal and maxillary arteries.
The auriculotemporal nerve runs up through the upper part of the gland with the superficial temporal vessels, and parotid lymph nodes lie within and on it.
Inside the gland the facial nerve divides, usually into an upper temporofacial and a lower cervicofacial trunk. These form a variable network, then emerge from the anterior border as five terminal branches.
| Branch | Course | Main muscles |
|---|---|---|
| Temporal | Crosses the zygomatic arch | Frontalis, upper orbicularis oculi, auricular muscles |
| Zygomatic | Across the zygomatic bone | Orbicularis oculi |
| Buccal | Forward with the parotid duct | Buccinator, zygomaticus, levators of the upper lip, orbicularis oris |
| Marginal mandibular | Along the lower border of the mandible | Depressor anguli oris, depressor labii inferioris, mentalis |
| Cervical | Down into the neck | Platysma |
Blood supply and innervation
The gland is supplied by the external carotid artery and its branches within it, and drained by the retromandibular vein. Lymph passes to the parotid nodes and then to the deep cervical chain.
The secretomotor supply is parasympathetic and comes from the glossopharyngeal nerve by an indirect route:
- Preganglionic fibres leave the inferior salivatory nucleus in the glossopharyngeal nerve.
- They travel in its tympanic branch to the tympanic plexus on the promontory of the middle ear.
- They leave as the lesser petrosal nerve and pass through the foramen ovale, usually, to the otic ganglion.
- Postganglionic fibres reach the gland on the auriculotemporal nerve (V3).
Sympathetic fibres arrive with the external carotid plexus. The great auricular nerve (C2, C3) supplies the capsule and the skin over the gland.
Clinical relevance
Most parotid surgery is about removing a tumour without damaging the facial nerve.
- Pleomorphic adenoma: the commonest parotid tumour, benign but recurs if its capsule is breached.
- Facial weakness with a parotid lump: suggests malignancy until proved otherwise.
- Finding the nerve trunk at parotidectomy: the tragal pointer (the nerve lies deep and slightly below its tip), the tympanomastoid suture and the posterior belly of digastric guide the surgeon to the trunk.
- Frey's syndrome: sweating and flushing of the cheek on eating after parotidectomy, when cut auriculotemporal parasympathetic fibres regrow into the sweat glands of the skin.
- Great auricular nerve injury: numbness of the ear lobe after parotid surgery.
- Cheek lacerations: a deep wound across masseter can divide both the duct and buccal branches.
On the specimen
The dissection shows the gland with the facial nerve branches fanning out from its anterior border, and the muscles of the face they supply.
- Duct or nerve on masseter: the duct is a thick, pale, tubular cord running horizontally; buccal nerve branches are thinner and more numerous.
- Accessory parotid gland: a small lobule of glandular tissue on the duct, just below the zygomatic arch.
- Superficial temporal or facial artery: the superficial temporal artery rises in front of the tragus; the facial artery crosses the lower border of the mandible at the front of masseter and winds towards the angle of the mouth.
- Zygomaticus major or minor: major runs from the zygomatic bone to the angle of the mouth; minor lies medial to it and goes to the upper lip.
- Levator anguli oris: deeper, from the canine fossa of the maxilla to the angle of the mouth.
- Depressor anguli oris: the triangular muscle below the angle of the mouth, arising from the mandible.