Parotid Gland

Fig. 8.65 — Parotid Gland. (A) Lateral view showing facial nerve branches and parotid duct. (B) Cross-sectional relations. — Gray's Anatomy for Students

1. Overview

2. Location & Borders

3. Lobes

• The superficial lobe lies lateral to the facial nerve, overlying the lateral surface of the masseter.
• The deep lobe lies medial to the facial nerve, situated between the mastoid process and the mandibular ramus; it can extend into the pretyloid compartment of the parapharyngeal space.

4. Parotid (Stensen's) Duct

• Leaves the anterior edge of the gland midway between the zygomatic arch and the corner of the mouth.
• Traverses across the external surface of the masseter muscle in a transverse direction.
• At the anterior border of the masseter, turns medially into the buccal fat pad.
• Pierces the buccinator muscle and opens into the oral cavity opposite the crown of the second upper molar tooth.

An accessory parotid gland may be present superiorly related to the duct.

5. Structures Passing Through the Gland

1. Facial nerve [CN VII] — most superficial
2. Retromandibular vein — intermediate
3. External carotid artery — deepest

6. Facial Nerve Relations

• Upper divisions: temporofacial branches
• Lower divisions: cervicofacial branches

Surgical landmark identification of the facial nerve:

• Tympanomastoid suture line
• Posterior belly of digastric muscle (marks depth of nerve)
• Tragal pointer (nerve lies ~1 cm deep and inferior to the tip of the tragal cartilage)
• Retrograde identification from a peripheral branch

7. Blood Supply

Arterial

• The external carotid artery courses medially within the gland, dividing into:
  • Maxillary artery (passes horizontally, deep to the mandible)
  • Superficial temporal artery (exits the upper border, gives off the transverse facial artery)
• Posterior auricular artery — given off before the terminal division

Venous

• The superficial temporal vein and maxillary vein join within the gland to form the retromandibular vein.
• The retromandibular vein divides below the gland into:
  • Posterior branch → joins external jugular vein
  • Anterior branch → joins facial vein → drains to internal jugular vein (lies just deep to the marginal mandibular branch of CN VII)

8. Nerve Supply (Innervation)

Secretomotor (Parasympathetic) Pathway

1. Glossopharyngeal nerve [CN IX] — provides preganglionic parasympathetic fibers via the tympanic branch (Jacobson's nerve) → tympanic plexus → lesser petrosal nerve
2. Preganglionic fibers synapse in the otic ganglion (just inferior to foramen ovale)
3. Postganglionic fibers travel with the auriculotemporal nerve (branch of V3) → parotid gland

Sympathetic

• Superior cervical ganglion supplies postganglionic sympathetic fibers (vasoconstrictor to the gland)

Sensory

• Auriculotemporal nerve (branch of mandibular nerve [V3], exits skull via foramen ovale) provides sensory innervation to the gland and the external ear; it also carries the secretomotor fibers described above.

Skin overlying the gland

• The great auricular nerve (C2, C3) — divides into anterior and posterior branches — provides cutaneous innervation. The posterior branch can sometimes be preserved during parotidectomy to reduce auricular numbness.

9. Lymphatic Drainage

10. Histology

11. Clinical Correlations

Frey's Syndrome (Auriculotemporal Syndrome)

Parotid Stones (Sialolithiasis)

Parotid Tumors

• ~90% of all salivary gland neoplasms occur in the parotid.
• ~75% are benign; ~25% are malignant or of variable aggressiveness.
• Most common benign tumor: Pleomorphic adenoma (mixed tumor)
• Common benign tumor: Adenolymphoma (Warthin's tumor)
• Malignant tumors (in descending frequency): mucoepidermoid carcinoma, adenoid cystic carcinoma, adenocarcinoma, epidermoid carcinoma, undifferentiated carcinoma, carcinoma ex pleomorphic adenoma.
• Deep lobe tumors can extend into the pretyloid compartment of the parapharyngeal space, presenting as a parapharyngeal mass.
• Facial nerve sacrifice risk must be considered in all parotid surgery; damage to upper branches prevents voluntary eyelid closure (risk of corneal injury); lower branch damage causes facial asymmetry.

Acute Suppurative Parotitis

Mumps Parotitis

Parotidectomy

• The facial nerve divides the gland into superficial and deep lobes and is the critical surgical landmark.
• Superficial parotidectomy (preserving CN VII) is the procedure of choice for most benign tumors.
• Total parotidectomy may involve the external carotid artery medially.

Q1. Parotid Gland — 20 Marks

Fig. — Parotid Gland. (A) Lateral view showing facial nerve branches, parotid duct, and vessels. (B) Cross-sectional relations. — Gray's Anatomy for Students

(a) Presenting Parts — [5 Marks]

Location & Shape

• the ramus of the mandible anteriorly
• the base of the skull superiorly
• the mastoid process posteriorly

• Superiorly up to the zygomatic arch
• Inferiorly down to the lower border of the mandible
• Anteriorly halfway across the masseter muscle (and over the sternocleidomastoid posteriorly)

Lobes

• Superficial lobe — 80% of the parenchyma; lies lateral to the facial nerve, overlying the masseter
• Deep (retromandibular) lobe — lies medial to the facial nerve, between the mastoid process and mandibular ramus; can extend into the pretyloid compartment of the parapharyngeal space

Parotid (Stensen's) Duct

• Leaves the anterior border of the gland midway between the zygomatic arch and the corner of the mouth
• Runs horizontally over the masseter muscle
• At the anterior border of masseter, turns medially through the buccal fat pad
• Pierces the buccinator muscle
• Opens into the oral cavity at the level of the crown of the 2nd upper molar tooth

Accessory parotid gland: Present in 21–61% of individuals; lies on the masseter anterior to Stensen's duct, with a secondary duct joining the main duct.

Lymphatics

(b) Capsule — [2 Marks]

Formation

• Vessels, nerves (facial nerve), and lymph nodes are all trapped within the capsule/substance of the gland
• The capsule merges with the investing (deep cervical) fascia — from the zygoma and temporomandibular joint above, over the masseter anteriorly, to the styloid base, posterior belly of digastric, and sternocleidomastoid posteroinferiorly

Structure

• The capsule is formed from the split investing layer of the deep cervical fascia (parotidomasseteric fascia)
• Superficial part is thin and closely related to the tragal and conchal cartilage
• Deep part is thick and attaches to the mastoid process
• The thick inferior portion separates the parotid from the submandibular gland
• The superficial musculoaponeurotic system (SMAS) is closely approximated to this capsule

Clinical Importance of Capsule

(c) Structures Passing Through the Gland — [5 Marks]

1. Facial Nerve [CN VII] — Most Superficial

• Exits the skull through the stylomastoid foramen (posterolateral to styloid process, anteromedial to mastoid process)
• Enters the posteromedial surface of the parotid and forms the pes anserinus (goose's foot)
• Divides into upper (temporofacial) and lower (cervicofacial) divisions within the gland
• Five terminal branch groups emerge from the gland's borders:

The facial nerve divides the parotid into superficial (80%) and deep (20%) lobes — Patey's faciovenous plane.

2. Retromandibular Vein — Intermediate

• Formed within the gland by the union of the superficial temporal vein and maxillary vein
• Passes inferiorly through the gland
• Divides just below the inferior border into:
  • Posterior branch → joins the posterior auricular vein → external jugular vein
  • Anterior branch → joins the facial vein → internal jugular vein (lies just deep to the marginal mandibular branch of CN VII — surgical landmark)

3. External Carotid Artery — Deepest

• Enters via the inferior border of the gland
• Gives off the posterior auricular artery within the gland
• Divides into its two terminal branches near the lower border of the ear:
  • Maxillary artery — passes horizontally, deep to the mandible
  • Superficial temporal artery — exits the superior border after giving off the transverse facial artery

Other Structures (Embedded or Related)

• Intraparotid lymph nodes — embedded within the substance (particularly in superficial lobe)
• Great auricular nerve (C2, C3) — runs on the surface of the gland
• Auriculotemporal nerve — enters and carries secretomotor fibers to the gland

(d) Nerve Supply — [5 Marks]

1. Secretomotor (Parasympathetic) — The Main Pathway

Inferior salivatory nucleus (medulla)
        ↓
Glossopharyngeal nerve [CN IX]
        ↓
Jacobson's nerve (tympanic branch of CN IX)
→ enters via inferior tympanic canaliculus
        ↓
Tympanic plexus (in middle ear)
        ↓
Lesser petrosal nerve (preganglionic parasympathetic)
→ exits skull via foramen ovale (or a small canal near it)
        ↓
Otic ganglion (just below foramen ovale, medial to mandibular nerve V3)
→ SYNAPSE here
        ↓
Postganglionic secretomotor fibers
→ join the AURICULOTEMPORAL NERVE (branch of V3)
        ↓
Parotid gland

2. Sympathetic

• Postganglionic fibers from the superior cervical ganglion travel along the external carotid artery plexus → parotid gland
• Effect: vasoconstriction; produces small amounts of thick, mucoid saliva

3. Sensory

• Auriculotemporal nerve (branch of V3, mandibular division of trigeminal [CN V])
  • Exits skull through foramen ovale
  • Provides sensory innervation to the parotid gland and the skin overlying it, the external acoustic meatus, and the auricle

4. Skin Overlying the Gland

• Great auricular nerve (C2, C3) — anterior and posterior branches; provides cutaneous sensation over the parotid region and lower part of the auricle

(e) Applied Anatomy — [3 Marks]

1. Frey's Syndrome (Auriculotemporal/Gustatory Sweating Syndrome)

• Cause: Injury to the auriculotemporal nerve (during parotidectomy, incision for parotid abscess, or trauma)
• Mechanism: Aberrant regeneration — the cut parasympathetic secretomotor fibers regrow and reinnervate the cutaneous sweat glands (which are normally supplied by sympathetic fibers but also respond to ACh)
• Features: At mealtimes, the skin over the parotid region becomes red, hot, and sweaty (gustatory sweating and flushing); cutaneous hyperaesthesia may also be present
• Treatment: Botulinum toxin injection into the affected skin (blocks ACh release)

2. Parotid Tumors

• ~90% of salivary gland neoplasms occur in the parotid gland
• ~75% benign, ~25% malignant or intermediate
• Most common benign: Pleomorphic adenoma (mixed tumor) — slow-growing, painless, at the angle of the jaw; sudden rapid growth + pain = malignant transformation
• Adenolymphoma (Warthin's tumor) — arises in the lower pole of the parotid at the level of the lower border of mandible, slightly lower than pleomorphic adenoma; bilateral in 10%
• Malignant tumors (decreasing order): Mucoepidermoid carcinoma > Adenoid cystic carcinoma > Adenocarcinoma > Epidermoid carcinoma > Undifferentiated carcinoma
• Facial nerve involvement: Any parotid tumor must be assessed for its relation to CN VII branches. Damage to upper branches → inability to close eye (risk of corneal ulceration); damage to lower branches → facial asymmetry

3. Parotidectomy & Facial Nerve Landmarks

1. Tragal pointer — facial nerve lies ~1 cm deep and inferior to the tip of the tragal cartilage
2. Tympanomastoid suture line — nerve exits just anterior to this
3. Posterior belly of digastric — marks the depth of the nerve
4. Retrograde identification — tracing peripheral branches back to the trunk

4. Acute Parotitis & Abscess

• Infection ascends from the oral cavity (poor oral hygiene, dehydration)
• Features: brawny, oedematous swelling with signs of inflammation
• Fluctuation is a late sign due to the thick, unyielding fascial capsule
• Parotid calculi (stones): less common than submandibular stones (parotid secretion is watery); cause pain on salivation — lemon juice test reproduces symptoms