Salivary Glands Anatomy - MU

• Salivary glands secrete 1-1.5 L of saliva daily.

Major Salivary Glands

• There are 3 pairs of major salivary glands.
• Parotid, submandibular, and sublingual glands are the major salivary glands.

Minor Salivary Glands

• Thousands of minor salivary glands exist in the oral cavity and pharynx.
• Labial, buccal, glossopalatine, palatine, and lingual glands.

Nature of Secretion & % of Saliva Secreted

• Parotid gland: serous secretion; 45% of saliva secreted
• Submandibular gland: seromucinous secretion; 45% of saliva secreted
• Sublingual gland: mucinous secretion; 5% of saliva secreted
• Minor salivary glands: 5% of saliva secreted

Surgical Anatomy of Parotid Gland - Embryology

• Parotid gland development occurs during the 6th-8th weeks of gestation.
• The parotid gland is the first to develop.
• The parotid gland grows in a posterior direction as the facial nerve grows anteriorly so the developing parotid surrounds the facial nerve.
• It is the last to become encapsulated after lymphatics develop, resulting in entrapment of lymphatics in the parenchyma of the gland.
• Salivary epithelial cells are often included within these lymph nodes.
• Likely playing a role in Warthin's tumors and lymphoepithelial cysts development within the parotid gland.
• Other major salivary glands do NOT have intraparenchymal lymph nodes.

Parotid Region - Characters

• It’s the region on the lateral surface of the face that comprises the parotid gland & the structures immediately related to it.
• The gland can be felt only in pathological conditions.

Location

• Located below and in front of the external auditory meatus
• Occupies the deep hollow
• Behind ramus of mandible
• In front of SM

Size

• Largest of the salivary glands
• Craniocaudal dimension: 5-8 cm
• Ventral-dorsal dimension: 3-4 cm

Weight

• Weighs 14-28 g

Borders

• Anterior convex border
• Straight posterior border

Surfaces

• Lateral surface.
• Anteromedial surface.
• Posteromedial surface.

Lobes

• The facial nerve courses horizontally through the gland, dividing it into superficial and deep lobes.

Shape Externally

• Wedge-shaped when viewed externally
  • Base (Concave upper end): Lies above and related to cartilaginous part of external acoustic meatus
  • Apex (lower end): Lies below and Behind angle of mandible

Shape Horizontally

• Wedge-shaped in horizontal section
  • Base: In the lateral position
  • Apex: Against pharyngeal wall

Processes

• Glenoid process: Extends upward behind the temporomandibular joint (TMJ), in front of the external auditory meatus (EAM).
• Facial process: Extends anteriorly onto the masseter muscle.
• Accessory process (part): Small part of the facial process lying along the parotid duct.
• Pterygoid process: Extends forward from the deeper part, lies between the medial pterygoid muscle & ramus of mandible.
• Carotid process: Lies posterior to external carotid artery.

Capsule

• The parotid gland is enclosed in two capsules:
  • Inner: connective tissue capsule
  • Outer: dense fibrous capsule, derived from the investing deep cervical fascia.
• Deep cervical fascia extends upward, reaching the inferior border of the parotid gland, and splits into superficial & deep layers to enclose the gland.
  • Above the gland: the superficial layer attaches to the zygomatic arch, and the deep layer attaches to the tympanic plate of the temporal bone.

Stylomandibular Ligament

• A portion of fascia extending from the styloid process to the angle of the mandible.
• Separates the parotid gland from the submandibular gland.

Borders - Relations to the Parotid Gland

• Superficial (Lateral): Skin & superficial fascia, platysma, great auricular nerve, parotid lymph nodes
• Superior: External auditory meatus (EAM), temporomandibular joint (TMJ), its glenoid process is related to the auriculo-temporal nerve
• Postero-Medial: Carotid sheath with its contents, styloid process & attached muscles, facial nerve, posterior belly of digastric muscle, mastoid process, sternocleidomastoid
• Antero-Medial: Stylomandibular ligament, medial pterygoid, posterior border of ramus of mandible, masseter muscle, terminal branches of facial nerve

Parotid Bed

• Vein: Internal jugular vein
• Arteries: External and internal carotid arteries
• Nerves: Glossopharyngeal (IX), Vagus (X), Spinal accessory (XI), Hypoglossal (XII)
• Anatomic entries: Styloid process, styloglossus, stylopharyngeus, stylohyoid muscles

Structures Entering and Leaving the Parotid Gland

• Upper End
  • Enter: Superficial temporal vein
  • Leave: Superficial temporal artery, auriculotemporal nerve, temporal branch of the facial nerve
• Lower End
  • Leave: Cervical branch of the facial nerve, retromandibular (posterior facial) vein & its 2 divisions
• Posteromedial Surface
  • Enter: External carotid artery, facial nerve
• Anteromedial Surface
  • Enter: Maxillary vein
  • Leave: Maxillary artery
• Anterior Border
  • Leave: Zygomatic branch of facial nerve, buccal branch of facial nerve, mandibular branch of facial nerve, parotid duct, transverse facial branch of superficial temporal artery

Structures within the Parotid Gland

• Auriculotemporal nerve
• External carotid artery
• Retromandibular vein
• Facial nerve
• Few lymph nodes scattered in the substance of the gland.

Facial Nerve Course

• Enters the posterior surface of the parotid gland, 1 cm from its emergence through the stylomastoid foramen, midway between the angle of the mandible & cartilaginous ear canal.
• At birth, the child has no mastoid process, so stylomastoid foramen is subcutaneous.
• About 1 cm from its entrance into the gland, it divides to form 5 branches: temporal, zygomatic, buccal, mandibular, cervical.
  • In most individuals, an initial bifurcation called the pes anserinus forms upper temporofacial & lower cervicofacial divisions, but 6 major patterns of branching, based on a series of simple to complex arrangements, have been distinguished.

Parotid (Steensen's) Duct

• Length: About 2 inches.
• Course: Emerges from the facial process of the parotid, passes forward over the lateral surface of the masseter about a fingerbreadth below the zygomatic arch, accompanied by transverse facial vessels (above) and upper buccal branches of the facial nerve (below).
• Turns around the anterior border of the masseter muscle.
• Pierces: Buccal pad of fat, buccopharyngeal fascia, buccinator muscle, buccal mucosa.
• Opens into the vestibule of the mouth on a small papilla, opposite the 2nd upper molar tooth.

Arterial Supply to the Parotid Gland

• External Carotid Artery: Enters the inferior surface of the parotid gland and divides at the level of the neck of the mandible into the maxillary and superficial temporal arteries.
• Superficial Temporal Artery: Gives rise to the transverse facial artery.
• Each of these branches emerges separately from the superior or anterior surface of the gland.

Venous Drainage of the Parotid Gland

• Maxillary & superficial temporal veins drain into the retromandibular vein.
  • Superficial temporal vein enters the superior surface of the parotid gland and receives the maxillary vein to become the retromandibular vein.
  • While still within the gland, the retromandibular vein divides into a posterior branch, which joins the posterior auricular vein to form the external jugular vein, and an anterior branch, which emerges from the gland to join with the anterior facial vein, forming the common facial vein, a tributary to the internal jugular vein.

Lymphatic Drainage of the Parotid Gland

• Parotid lymph nodes drain into deep cervical lymph nodes.

Nerve Supply to the Parotid Gland

• Parasympathetic secretomotor fibers originate from the inferior salivatory nucleus of the 9th cranial nerve in the medulla oblongata, travel via the tympanic branch to form the tympanic plexus in the middle ear, continue via the lesser petrosal nerve to the otic ganglion, and then postganglionic secretomotor parasympathetic fibers travel via the auriculotemporal nerve to supply the parotid gland.
• Sympathetic: The sympathetic plexus of the carotid sheath around the external carotid artery.
• Sensory:
  • Auriculotemporal nerve (branch of the mandibular division of the trigeminal nerve [CN V3]) ascends from the upper end of the parotid gland to supply the skin of the scalp above the auricle
  • Great auricular nerve (C2,3)

Otic Ganglion

• Small parasympathetic ganglion that is functionally associated with the glossopharyngeal nerve.
• Located in the infratemporal fossa, just below the foramen ovale & medial to the mandibular nerve.

Great Auricular Nerve

• Course: Reaches the posterior border of the sternocleidomastoid muscle and proceeds across the surface of the parotid gland, following the course of the external jugular vein.
• Sacrifice: Sacrificed during parotidectomy.
• Injury Results in numbness in: Preauricular region, lower auricle, lobe of the ear (resolves after 4-6 months)

Auriculotemporal Nerve

• A branch of the mandibular nerve traverses the upper part of the parotid & emerges with the superficial temporal vessels from the superior surface of the gland.
• Within the gland, the auriculotemporal nerve communicates with the facial nerve.
• Course: Usually, the order of the structures from tragus anteriorly is:
  • Auriculotemporal nerve.
  • Superficial temporal artery and vein.
  • Temporal branch of the facial nerve.
• The auriculotemporal nerve carries:
  • Sensory fibers from the 5th nerve.
  • Secretomotor fibers from the 9th nerve.
• Produces Frey's syndrome, in which the skin anterior to the ear sweats during eating (“gustatory sweating”).

Frey’s Syndrome

• Recurrent episodes of localized facial flushing and/or sweating in the area over the parotid gland in response to gustatory stimuli.
• Etiology: Aberrant nerve regeneration after injury such that parasympathetic fibers migrate into the cutaneous sympathetic nerves that supply the sweat glands.

Submandibular Gland

• Anterior Cervical Triangle
  • Boundaries: Lateral (sternocleidomastoid muscle), superior (inferior border of the mandible), medial (anterior midline of the neck)
  • This large triangle is subdivided into four more triangles: submandibular, mental, carotid, muscular.

Submandibular Triangle

• Demarcated by
  • Above: inferior border of the mandible
  • Below: anterior & posterior bellies of the digastric muscle
• Contents: Submandibular salivary gland (“the largest structure in the triangle”), a number of vessels, nerves & muscles.

Surgical Planes

• The contents of the triangle are best described in 4 layers or surgical planes, starting from the skin It must be noted that severe inflammation of the submandibular gland can destroy all traces of normal anatomy.

First Surgical Plane

• Roof of the submandibular triangle
  • Composed of: skin, superficial fascia enclosing platysma muscle & fat, mandibular & cervical branches of the facial (VII) nerve A. Mandibular (or marginal mandibular)
    • Passes approximately 3 cm below the angle of the mandible
    • Innervates muscles of the lower lip and muscles of the corner of the mouth
    • Injury results in severe drooling at the corner of the mouth
  • B. Cervical nerve: Anterior branch ("Ramus colli mandibularis")
    • Crosses the mandible superficially to the facial artery & vein joins the mandibular branch
    • Innervates the platysma & communicates with the anterior cutaneous nerve of the neck
    • Injury results in minimal drooling that will disappear in 4 to 6 months

Second Surgical Plane

• Contents of the submandibular triangle
• Contains XII nerve, Facial v., Submental a., Middle Gland, Jugular v. and Carotid a.
• The superficial portion of the submandibular gland is exposed.

Third Surgical Plane

• Floor of the submandibular triangle
• Contains Styloglossus m., Hyoglossus m., Middle constrictors m., Submandibular duct, Lingual nerve and Mylohyoid m.

Fourth Surgical Plane

• Basement of the submandibular triangle
• Deep portion of submandibular gland, lingual nerve, and hypoglossal (XII) nerve.

Relations

• Surrounded by: C-T capsule, dense fascial capsule derived from investing layer of deep cervical fascia
• Its deep part is continuous with its superficial part around the posterior border of the mylohyoid muscle
• Its superficial part lies in the digastric triangle between the mylohyoid & body of the mandible (superficial to mylohyoid)
• Small deep lies deep to mylohyoid and superficial to hyoglossus Lie within
  • Anterior: anterior belly of the digastric
  • Posterior: posterior belly of digastric, stylohyoid muscle
  • Medial (Deep): Mylohyoid
  • Lateral: lies in contact with the submandibular fossa on the medial surface of the mandible
  • Inferolateral (superficial): Skin, superficial fascia, platysma muscle, investing layer of deep cervical fascia, submandibular lymph nodes Crossed By:
    • Cervical branch of facial nerve and facial vein
    • The facial artery ascends into digastric triangle
    • Deeply grooves posterior end of the gland
    • Passes between the lateral surface of the gland & the bone reaches base of the mandible where it pierces deep fascia to ascend to face

Anatomic Relations

• Lingual nerve and Styloglossus muscle
• Digastric muscle (posterior belly)
• Stylohyoid muscle
• Hyoglossus muscle
• Submandibular gland superficial and deep portions
• Mylohyoid muscle (cut)

Deep Part of Submandibular Salivary Gland

• Located deep to mylohyoid and superficial to hyoglossus
• Next to lingual nerve and submandibular ganglion
• Below the hypoglossal nerve
• Deep to the hyoglossus and styloglossus

Submandibular Ducts

• Emerges from the anterior end of its deep part, then passes beneath the mucous membrane of floor of mouth
• Crossed by the lingual nerve
• Lies between the sublingual gland & genioglossus muscle
• Opens into the floor of mouth at the side of the frenulum of the tongue
• The frenulum of the tongue in midline = a fold of mucous membrane connects undersurface of tongue to the floor of mouth

Submandibular Lymph Nodes

• drain into deep cervical lymph nodes

Nerve Supply

• Preganglionic fibers from superior salivatory nucleus of facial nerve via Chorda tympani nerve to join Lingual nerve and then to Submandibular ganglion.
• Postganglionic Parasympathetic Secretory fibers from ganglion via Lingual nerve into the gland
• Sympathetic fibers from plexus of nerves around Facial & Lingual arteries, and Lingual nerve

Sublingual Gland

• Lies beneath mucous membrane of the floor of mouth in the sublingual fold, and it's close to the midline.
• Smallest of the three main salivary glands
• Contains both serous & mucous acini
• The gland opens by numerous small ducts into the floor of mouth on the summit of sublingual fold

Relations

• Posterior: deep part of the submandibular gland
• Medial (Deep): Genioglossus, lingual nerve, submandibular duct
• Lateral (superficial): Is the sublingual fossa of the mandible
• Superior: Mucous membrane of the floor of the mouth, forming sublingual fold
• Inferior: Supported by mylohyoid muscle.

Blood Supply & Lymphatic Drainage

• Same as the submandibular gland.

Nerve Supply

• Parasympathetic: As submandibular gland.
• Postganglionic: Fibers pass to gland via the Lingual nerve
• From plexus of nerves around Facial & Lingual arteries