Describe the anatomy of the parotid gland.
Superior : Corresponds to the posterior 2/3 of the lower border of the zygomatic arch.
Anterior : May extend to the anterior border of massester
Inferior : Along the ramus of the mandible
Posterior : In front of the external acoustic meatus, mastoid process and anterior border of SCM
The parotid gland is divided into a larger superficial and a smaller deep lobe. It is enclosed within a parotid sheath derived from the investing layer of the deep cervical fascia.
Describe the surface markings of the parotid duct.
The parotid duct lies in the middle 1/3rd of a line drawn along an axis from the tragus of the ear to a point between the ala of the nose and the lateral commissure of mouth. It overlies the masseter, pierces the buccinator and opens within the buccal vestibule at the level of the upper 2nd molar tooth (Stensen’s duct).
Describe the blood supply to the parotid gland
Arterial supply : Branches from the external carotid via the superficial temporal and posterior auricular arteries
Venous drainage : Drains into the retromandibular vein
What is the nerve supply to the parotid gland?
Sensory fibres are derived from the auriculotemporal and great auricular nerves.
Parasymphathetic fibres are derived from the glossopharyngeal nerve.
Sympathetic fibres are derived from the external carotid nerve plexus.
Note: Although the facial nerve runs within the parotid gland it does not supply it
Name the structures within the substance of the parotid gland
From superficial to deep the structures within the substance of the parotid are:
Facial nerve: The five branches of the facial nerve (temporal, zygomatic, buccal, marginal mandibular and cervical) divide within the parotid gland itself.
Retromandibular vein (formed by the union of the superficial temporal and maxillary veins).
External carotid artery and its terminal branches superficial temporal and maxillary arteries.
Branches of the great auricular nerve
Lymph nodes.
What are the complications associated with parotid gland surgery?
General risks:
Pain
Bleeding
Haematoma
Infection
Scarring
Specific risks:
Facial nerve injury (resulting in temporary or permanent facial weakness)
Frey’s syndrome (gustatory sweating)
Spillage leading to reoccurrence of disease
Sinus/ fistula
How would you investigate a parotid lump?
History and examination of the neck lump.
FNA
Imaging (CT/MRI)
What is Frey’s syndrome?
Frey’s syndrome refers to erythema and sweating along the auriculotemporal nerve territory on eating, thinking or talking about food. The auriculotemporal nerve (from mandibular division of trigeminal) normally carries parasympathetic fibres to the secretomotor fibres of parotid gland (responsible for salivation). The sympathetic fibres arising from the superior cervical ganglion is responsible for erythema and sweating over the cheek and scalp region.
Frey's syndrome is due to damage to these autonomic fibers and misdirected regenerative process of the auriculotemporal nerve. During the process of healing, the regenerating parasympathetic fibers may wrongly join the sympathetic fibers, which supplies sweat glands and blood vessels resulting in erythema and sweating instead of salivation
Name the blood supply to the submandibular gland.
The submental artery (from the facial artery) and the lingual artery (from the external carotid artery).
What is the nerve supply to the submandibular gland?
Parasympathetic fibres from the facial nerve are conveyed via the chorda tympani nerve and lingual nerve to synapse and supply secretomotor function to the gland.
Sympathetic fibres from around arteries supplying the gland provide vasoconstriction.
Describe where the submandibular duct opening lies
The submandibular duct (Wharton's duct) is approximately 5 cm long and opens lateral to the lingual frenulum.
Name the nerves at risk of injury during submandibular gland surgery.
Marginal mandibular branch of facial nerve
Lingual nerve
Hypoglossal nerve
Nerve to mylohyoid
Where are the sublingual glands found?
The sublingual glands are found deep in the floor of the mouth between the mandible and the genioglossus muscle. Numerous small sublingual ducts open into the floor of the mouth along the sublingual folds
Describe the blood supply to the sublingual glands.
The blood supply is from the sublingual artery (from the lingual artery) and submental artery (from the facial artery).
Describe the nerve supply to the sublingual glands
Parasympathetic fibres from the facial nerve are conveyed via the chorda tympani nerve and lingual nerve to synapse and supply secretomotor function to the gland.
Sympathetic fibres from around arteries supplying the gland provide vasoconstriction.
Why are stones in the submandibular gland more common than in the parotid gland?
The parotid gland produces serous saliva whereas the submandibular gland produces thick mucoid saliva and also has a higher concentration of calcium.
The submandibular duct is longer, flows against gravity and has a smaller orifice when compared to that of the parotid duct.