Parotid Region Anatomy

Parotid Region Anatomy

• The parotid region is located below and in front of the ear, and below the zygomatic arch.
• Key features include the parotid gland and masseter muscle (part of the mastication group).

Masseter Muscle

• The masseter muscle arises from the zygomatic arch.
• Structurally contains three heads (though typically described as two), which are fused on the arch.
• Anteriorly, the three sets fuse. Posteriorly, they diverge to allow for the passage of the masseteric nerve and artery.
• The superficial part is the largest, arising from the anterior two-thirds of the zygomatic arch. Its fibers slope down 45 degrees and insert into a wide area of the mandible's lower border and ramus.
• The upper part of the muscle is covered by aponeurotic fibers to slide over structures, while the lower portion is fleshy.
• Middle and deep parts arise from the middle and deep surfaces of the arch respectively, inserting vertically downwards into the mandibular ramus. Their insertions fuse with superficial fibers anteriorly but remain separate posteriorly.
• The masseteric nerve passes between the deep and intermediate parts, and a branch of the superficial temporal/transverse facial artery runs between the superficial and intermediate parts.
• The artery is the primary blood supply, and the artery accompanying the nerve is smaller.
• Nerve supply: masseteric branch of the mandibular nerve's anterior division.
• Action: Closes the jaw, elevates and pulls forward the angle of the mandible.

Parotid Gland

• Predominantly serous salivary gland, with few mucous acini.
• Irregular shape, filling the space between the mastoid process, mandibular ramus, and styloid process.
• Regions include upper and lower poles, lateral, anterior, and deep surfaces.
• Enclosed by a tough capsule called the parotid sheath (part of the deep cervical fascia).
• Mumps (viral infection) causes swelling within the tight fibrous capsule.
• Upper pole: small, concave, adheres to the external acoustic meatus cartilage, adjacent to the temporomandibular joint capsule.
• Lower pole: rounded, below/behind mandible angle, indented by mandible & sternocleidomastoid. Overlaps the posterior belly of digastric.
• Lateral surface: subcutaneous and almost flat.
• Anterior surface: U-shaped, wraps around mandibular ramus, with masseter externally and medial pterygoid internally. Stylomandibular ligament separates it from medial pterygoid and submandibular gland. Anterolateral border is formed by merging of the lateral and anterior surfaces.
• Deep surface (posteromedial): irregular and complex, indented by mastoid process/muscles, styloid process/muscles/ligaments. External carotid artery enters the gland through the lower part. Styloid process separates it from internal jugular vein and internal carotid artery. Facial nerve branches enter between styloid and mastoid processes.
• Contents (superficial to deep): facial nerve, retromandibular vein, external carotid artery.
• Branches from facial nerve emerge behind the anterior border.
• The external carotid artery and its branches are the deepest.
• The gland also contains preauricular lymph nodes, and filaments of auriculotemporal nerve with secretomotor fibers.
• Lymph drainage to lymph nodes within the parotid sheath, then to cervical nodes with the external carotid artery.

Parotid Duct

• 5 cm long (Stensen's duct).

• Passes across masseter, around its anterior border, and pierces the buccinator.

• Palpable between the intertragic notch and the philtrum midpoint.

• Opens on the cheek's mucous membrane opposite the second upper molar.

• A valve-like flap prevents gland inflation during intraoral pressure.

Accessory Parotid Gland

• Usually located on the masseter, between duct and zygomatic arch.
• Several ducts connect it to the parotid duct.
• Located on the tendinous portion of masseter.

Blood Supply

• Branches from the external carotid artery.
• Venous return to the retromandibular vein.

Nerve Supply

• Secretomotor fibers: otic ganglion via auriculotemporal nerve. Pre-ganglionic fibers from inferior salivary nucleus in medulla via glossopharyngeal nerve, tympanic branch, tympanic plexus, and lesser petrosal nerve.
• Sympathetic fibers (vasoconstrictor): superior cervical ganglion via external carotid and middle meningeal artery plexus.
• Sensory fibers: auriculotemporal nerve. Parotid fascia receives sensory innervation from great auricular nerve (C2).

Development

• An ectodermal groove in the cheek becomes a tunnel; cell proliferation forms the gland.

Surgical Approach (Parotidectomy)

• S-shaped incision (in front of ear, back to mastoid, down/forward below mandible angle).
• Skin incision includes platysma.
• Gland retracted forward to expose posterior digastric, stylohyoid, & external meatus cartilage.
• Facial nerve approached in front of cartilage; stylomastoid branch (posterior auricular artery) is a superficial guide.
• Cartilage arrowhead points toward nerve.
• Parotid duct divided at masseter's anterior border.
• Total parotidectomy involves dissecting further, ligating external carotid, superficial temporal, maxillary arteries and veins. Styloid process may need fracturing, stylo-mandibular ligament may need division.