Parotid
PAROTID GLAND
The parotid gland is the largest of the salivary glands.
General
- The parotid gland is the largest of the salivary glands.
- Para = around
- Otic = ear
- Weight → about 25 g
Location
The parotid glands are situated in the pyramidal retromandibular fossa, or parotid bed.
Boundaries of Parotid Bed
-
Anteriorly:
Ramus of mandible with:
- Medial pterygoid
- Masseter
-
Posteriorly:
Mastoid process with:
- Sternocleidomastoid
- Posterior belly of digastric
- Superiorly: External acoustic meatus and temporomandibular joint
- Medially: Styloid apparatus
The gland overlaps these structures.
Skin over the gland is supplied by the great auricular nerve (C2, C3).
Capsule of Parotid Gland
The investing layer of the deep cervical fascia forms a capsule or parotid sheath.
It is supplied by the great auricular nerve.
Superficial Lamina
- Thick, strong, unyielding and adherent to the gland.
- Superiorly → attached to the inferior border of the zygomatic arch.
- Anteriorly → blends with the epimysium of masseter to form parotidomasseteric fascia.
Deep Lamina
- Thin.
- Attached to the tympanic plate.
- Attached to the styloid process.
- Stylomandibular ligament → thickened part of the deep lamina.
- It extends from the tip of styloid process to the angle of mandible.
Recent Concept
- Superficial Musculo-aponeurotic System (SMAS) is a single tissue plane in the face.
- It is composed of muscle fibres.
- It is composed of fibrous or fibroaponeurotic tissue.
- It is not directly attached to bone.
- Inferiorly, it becomes continuous with platysma in the neck.
- The superficial layer of the parotid capsule is a component of the SMAS, and not from the investing layer of deep cervical fascia.
Clinical Anatomy
Parotid Swellings
Parotid swellings are very painful due to the unyielding nature of the parotid fascia.
Mumps
- Mumps is an infectious disease of the salivary glands, usually the parotid, caused by a specific virus.
- Viral parotitis or mumps characteristically does not suppurate.
- Complications:
- Orchitis
- Pancreatitis
Accessory Parotid Gland
- It is a detached part of the parotid gland.
- It lies between the zygomatic arch and the parotid duct.
- It drains into the main parotid duct.
External Features of Parotid Gland
- The parotid gland resembles an inverted pyramid.
- Its apex is directed downward.
Apex
Directed downwards.
It overlaps the posterior belly of digastric.
Four Surfaces
- Superior surface (base)
- Superficial surface
- Anteromedial surface
- Posteromedial surface
Three Borders
- Anterior
- Posterior
- Medial
Relations of Parotid Gland
1. Apex
The apex is directed downwards.
It overlaps the posterior belly of digastric.
Structures Emerging Through Apex
- Cervical branch of facial nerve
- Anterior and posterior divisions of retromandibular vein
2. Superior Surface / Base
Forms the upper end of the gland.
It is small and concave.
Relations
- External acoustic meatus
- Posterior surface of temporomandibular joint
Structures Emerging Through Superior Surface
- Superficial temporal vessels
- Auriculotemporal nerve
3. Superficial Surface
It is the largest of the four surfaces.
It is Covered With
- Skin
-
Superficial fascia, containing:
- Anterior branches of the great auricular nerve
- Preauricular or superficial parotid lymph nodes
- Posterior fibres of platysma and risorius
- Superficial lamina of parotid fascia
- A few deep parotid lymph nodes embedded in the gland.
4. Anteromedial Surface
It is grooved by the posterior border of the ramus of the mandible.
Relations
- Masseter
- Lateral surface of the temporomandibular joint
- Posterior border of the ramus of mandible
- Medial pterygoid
-
Emerging branches of:
- Facial nerve
- Maxillary artery
5. Posteromedial Surface
It is moulded to the mastoid and styloid processes and the structures attached to them.
Relations
-
Mastoid process, with:
- Sternocleidomastoid
- Posterior belly of digastric
- Styloid process, with structures attached to it
-
Deep to the styloid apparatus:
- Internal carotid artery
- Internal jugular vein
- Last 4 cranial nerves
Structures Entering Through Posteromedial Surface
- Facial nerve
- External carotid artery
Borders of Parotid Gland
Anterior Border
Separates the superficial surface from the anteromedial surface.
Extends from the anterior part of the superior surface to the apex.
Structures Emerging From Anterior Border — Above Downwards
- Temporal branch of facial nerve
- Zygomatic branch of facial nerve
- Transverse facial vessels
- Upper buccal branch of facial nerve
- Parotid duct
- Lower buccal branch of facial nerve
- Marginal mandibular branch of facial nerve
In addition, the facial process of the accessory parotid glands lies on the parotid duct close to this border.
Posterior Border
Separates the superficial surface from the posteromedial surface.
It overlaps the sternocleidomastoid.
Structures Emerging Deep to Posterior Border
- Posterior auricular nerve
- Posterior auricular branch of facial nerve
Medial Edge / Pharyngeal Border
Separates the anteromedial surface from the posteromedial surface.
It is related to the lateral wall of the pharynx.
Structures Within the Parotid Gland
Three main structures are present within the parotid gland.
Facial nerve and its branches
Retromandibular vein
External carotid artery
Facial Nerve
- The facial nerve enters the posteromedial surface of the parotid gland.
-
It runs forward through the gland, crossing:
- Retromandibular vein
- External carotid artery
-
Behind the neck of the mandible, it divides into two branches:
- Temporofacial
- Cervicofacial
- These form a plexus called pes anserinus.
Terminal Branches of Pes Anserinus
- Temporal
- Zygomatic
- Buccal
- Marginal mandibular
- Cervical
These branches emerge along the anterior border and apex of the parotid gland.
Arteries and Veins
Arteries
- The external carotid artery enters the gland through its posteromedial surface.
- The maxillary artery leaves the gland through its anteromedial surface.
- The superficial temporal artery gives the transverse facial artery and emerges at the anterior part of the superior surface.
Veins
-
The retromandibular vein is formed within the gland by the union of:
- Superficial temporal vein
- Maxillary vein
-
In the lower part of the gland, the vein divides into:
- Anterior division
- Posterior division
- These emerge close to the apex (lower pole) of the gland.
Accessory Processes of Parotid Gland
-
Facial process
- Along the parotid duct.
- Lies between the zygomatic arch and parotid duct.
-
Pterygoid process
- Between mandibular ramus and medial pterygoid.
-
Glenoid process
- Between external acoustic meatus and temporomandibular joint.
- Poststyloid process.
Blood Supply
The parotid gland is supplied by the external carotid artery and its branches that arise within the gland.
The veins drain into:
- External jugular vein
- Internal jugular vein
Lymphatic Drainage
Lymph drains first to the parotid nodes.
From there, it drains to the upper deep cervical nodes.
Nerve Supply
1. Parasympathetic Nerves
- They are secretomotor.
- They reach the gland through the auriculotemporal nerve.
-
Preganglionic fibres:
- Begin in the inferior salivatory nucleus.
- Pass through:
- Glossopharyngeal nerve
- Tympanic branch
- Tympanic plexus
- Lesser petrosal nerve
- Relay in the otic ganglion.
- Postganglionic fibres pass through the auriculotemporal nerve and reach the gland.
2. Sympathetic Nerves
- They are postganglionic.
- They are vasomotor.
- They are derived from the plexus around the middle meningeal artery.
- These fibres start from the lateral horn of T1 segment of spinal cord.
- They synapse in the superior cervical ganglion.
-
Postganglionic fibres travel along branches of:
- External carotid artery
- Maxillary artery
- Their branches, e.g. middle meningeal artery
3. Sensory Nerves
- Sensory nerves to the gland come from the auriculotemporal nerve.
- The parotid fascia is innervated by sensory fibres of the great auricular nerve (C2, C3).
Parotid Lymph Nodes
Parotid lymph nodes lie:
- Partly in the superficial fascia
- Partly deep to the deep fascia over the parotid gland
They Drain
- Temple
- Side of scalp
- Lateral surface of auricle
- External acoustic meatus
- Middle ear
- Parotid gland
- Upper part of cheek
- Parts of eyelids and orbit
Efferents from these nodes pass to the upper group of deep cervical nodes.
Parotid Duct / Stenson’s Duct
- Parotid or Stenson’s duct is thick-walled.
- It is about 5 cm long.
- Nicolaus Steno → Dutch anatomist, 1638–86.
- It emerges from the middle of the anterior border of the gland.
- It runs forwards and slightly downwards on the masseter.
Course
- After emerging from the parotid gland, the duct runs forward on the masseter, between the upper and lower buccal nerves.
-
Then it runs medially along the anterior border of masseter and pierces:
- Buccal pad of fat
- Buccopharyngeal fascia
- Buccinator
- Oral mucosa
- Before piercing the mucosa, the duct runs obliquely forward.
- It opens into the vestibule of mouth opposite the crown of the upper 2nd molar tooth.
This typical course of the duct prevents air entry in the duct during blowing of mouth, as in trumpet blowing.
Clinical Anatomy
Probing of Parotid Duct
Probing the parotid duct is difficult due to its tortuous course.
Palpation of Parotid Duct
- The parotid duct can be rolled up and down against the tense masseter on clinching of teeth.
- The duct lies about one fingerbreadth below the zygomatic arch.
Parotid Sialography
- Parotid sialography is a radiological visualisation of the parotid duct and its tributaries.
- It is performed by injecting radio-opaque into the parotid duct through its oral opening.
Parotid Abscess
- A parotid abscess may be caused by spread of infection from the opening of the parotid duct in the mouth cavity.
-
Parotid abscess can be drained by:
- Horizontal incision
- Making many small holes known as Hilton’s method
- This is done below the angle of mandible.
Parotidectomy
Parotidectomy is the removal of the parotid gland.
Mixed Parotid Tumour
- It is a slow-growing, lobulated, painless tumour.
- There is no involvement of the facial nerve.
-
Malignant change is indicated by:
- Pain
- Rapid growth
- Fixity with hardness
- Involvement of facial nerve
- Enlargement of cervical lymph nodes
Parotid Calculi
-
Parotid calculi may be formed:
- Within the parotid gland
- In its Stenson’s duct
- They can be located by injecting a radio-opaque dye through its opening in the vestibule of the mouth.