Parotid

Function

• Predominantly a serous salivary gland
• Secretes saliva via the parotid duct into the oral cavity to facilitate mastication and swallowing

Embryology

• From ectoderm
• Forms as a groove in the cheek, with ectodermal cells in the blind end of that groove/tunnel forming the gland

Gross anatomy

• Average weight 25g
• Three surfaces - lateral, anterior and deep
• Roughly triangular when viewed from laterally
• Made up of a larger superficial lobe and a smaller deep lobe (deep to ramus of mandible)
• Irregular, lobulated, yellowish mass
• The two lobes are separated by the facial nerve
• Enclosed within an unyielding parotid capsule, derived from investing layer of deep cervical fascia
  • This fascia attaches to styloid process and mandible in front of the gland - the stylomandibular ligament, which separates parotid from submandibular gland
  • The fascia also connects the posterior parotid to the external auditory canal
• Can have an accessory parotid gland between the zygomatic arch above and parotid duct below

Parotid duct (of Stensen)

• Exits from front of gland
• 5cm long
• Lies on masseter
• Dives deeply around the muscle's anterior border, through buccal fascia, to open inside the cheek, opposite second molar upper tooth
• Can be an accessory parotid duct on the masseter between the duct and the zygomatic arch

Relations

• Below external acoustic meatus, between mandible and SCM
• Also projects forward onto surface of masseter
• Posteriorly lies over SCM - greater auricular nerve and EJV seen here
• Traversed by (from deep to superficial):
  • Auriculotemporal nerve - branch of mandibular division of trigeminal nerve, communicating with facial nerve within parotid. Damage is thought to relate to Frey's syndrome - sweating of pre-auricular skin when sweating.
  • External carotid artery - enters posteromedial surface and divides into maxillary artery and STA, and sometimes transverse facial artery, which tends to run parallel with but above the parotid duct
  • Retromandibular vein - superficial to ECA. Sometimes forms within the gland from superficial temporal and maxillary veins.
  • Facial nerve - stays superior to blood vessels - see separate topic - very variable anatomy
• May be covered by platysma antero-inferiorly

Blood supply

• Branches from ECA
• Venous drainage to the retromandibular vein

Lymphatic drainage

• Nodes within the parotid sheath

Innervation

• Fibres from inferior salivary nucleus in the medulla
  • Travel on glossopharyngeal nerve and its tympanic branch
  • Give rise to tympanic plexus on the promontory of the cochlear in the middle ear
  • These fibres pass via the lesser petrosal nerve to synapse in the otic ganglion
  • Post-ganglionic secretomotor fibres reach the parotid hitch-hiking along with the auriculotemporal nerve
• Sympathetic (vasoconstrictor) from the superior cervical ganglion
• Sensory
  • From parotid gland itself via auriculotemporal nerve
  • From parotid fascia via greater auricular nerve

Variant anatomy

• Accessory duct
• Accessory gland