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Salivary Glands& Disease October 2003 OMS 813
Embryology • The parotid anlagen are the first to develop, followed by the submandibular gland, and finally the sublingual gland. • Parenchymal tissue (secretory) of the glands arises from the proliferation of oral epithelium.
Embryology • The stroma (capsule and septae) of the glands originates from mesenchyme that may be mesodermal or neural crest in origin.
Parotid development13 • Although the parotid anlagen are the first to develop, they become encapsulated AFTER the SMG and SLG. • This delayed encapsulation is critical because after the encapsulation of the SMG and SLG but BEFORE encapsulation of the parotid, the lymphatic system develops.
Parotid development13 • Therefore, there are intraglandular lymph nodes and lymphatic channels entrapped within the parotid gland (PG). • PG is also unique because its epithelial buds grow, branch and extend around the divisions of the facial nerve.
Embryology • The epithelial buds of each gland enlarge, elongate and branch initially forming solid structures. • Branching of the glandular mass produces arborization. • Each branch terminates in one or two solid end bulbs.
Embryology • Elongation of the end bulb follows and lumina appears in their centers, transforming the end bulbs into terminal tubules. • These tubules join the canalizing ducts to the peripheral acini.
Duct Canalization • Canalization results from mitotic activity of the outer layers of the cord outpacing that of the inner cell layers • Canalization is complete by 6th month post conception.
Acinar cells • At around the 7-8th month in utero, secretory cells (acini) begin to develop around the ductal system.
Acinar cells of Salivary Glands Classified as either: • Serous cells: produce a thin watery secretion • Mucous cells: produce a more viscous secretion
Salivary gland secretory unit12 • Composed of terminal acini • Intercalated, striated and excretory ducts • Myoepithelial cells
Major glands/Secretions • Major SG are paired structures and include the parotid, submandibular and sublingual • Parotid: serous • Submandibular: mucous & serous • Sublingual: mucous
Salivary Function12 • Aid is mastication, deglutination • Salivary lysozyme, IgA and other antibacterial substances protect against caries and oral cavity infections • Saliva also aids in speech
Anatomy: Parotid Gland12,13 • Nearly 80% of the parotid gland (PG) is found below the level of the external auditory canal, between the mandible and the SCM. • Superficial to the posterior aspect of the masseter mm
Anatomy:Parotid Gland12 • Extensions of PG project to mastoid process • Down the anterior aspect of the SCM for a short distance • Around the posterior border of the mandible. • Superiorly to the to inferior margin of the zygomatic arch
Anatomy:Parotid Gland • CN VII branches roughly divide the PG into superficial and deep lobes while coursing anteriorly from the stylomastoid foramen to the muscles of facial expression.
Anatomy: Deep Lobe13 • The remaining 20% extends medially through the stylomandibular tunnel, which is formed • ventrally by the posterior edge of the ramus • dorsally by the anterior border of the SCM & posterior digastric muscle • deeply and dorsally by the stylomandibular ligament.
Anatomy: Parotid Duct • Small ducts coalesce at the anterosuperior aspect of the PG to form Stensen’s duct. • Runs anteriorly from the gland and lies superficial to the masseter muscle • Follows a line from the EAM to a point just above the commissure. • Is inferior to the transverse facial artery • It is 1-3 mm in diameter • 6cm in length
Anatomy: Parotid Duct • At the anterior edge of the masseter muscle, Stensen’s duct turns sharply medial and passes through the buccinator muscle, buccal mucosa and into the oral cavity opposite the maxillary second molar.
Anatomy: Parotid Fascia12 • Gland encapsulated by a fascial layer that is continuous w/the deep cervical fascia (DCF). • The stylomandibular ligament (portion of the DCF) separates the parotid and submandibular gland.
Anatomy: Parotid Lymphatics12 • Lymphatic drainage is to the superficial and deep cervical nodes • Preauricular lymph nodes (LN) in the superficial fascia drain the temporal scalp, upper face, anterior pinna • LN within the gland drain the parotid gland, nasopharynx, palate, middle ear and external auditory meatus
Parotid: Parasympathetic Innervation • Preganglionic parasympathetic (from CN9) arrives at otic ganglion via lesser petrosal n. • Postganglionic parasympathetic leaves the otic ganglion and distributes to the parotid gland via the auriculotemporal nerve.
Parotid: SympatheticInnervation • Postganglionic innervation is provided by the superior cervical ganglion and distributes with the arterial system
Parotid Anatomy: Great Auricular Nerve (C2,C3) • Emerges from the posterior border of the SCM at Erb’s point. • It crosses the mid-portion of the SCM about 6.5cm beneath the EAM. • Passes parallel and superior to the external jugular vein to supply the ear and pre-auricular region.
Parotid Anatomy: Auriculotemporal Nerve • Branch of V3 • Traverses the upper part of the parotid gland and emerges from the superior surface with the superficial temporal vessels. • It carries sensory fibers from the trigeminal and post-ganglionic parasympathetic (secretory)fibers.
Parotid Anatomy: Facial Nerve • Emerges at the level of the digastric muscle, through the stylomastoid foramen. • Main trunk divides at the pes anserinus (intraparotid plexus of CN7) into the upper temporofacial and lower cervicofacial divisions. • Before it enters gland, gives off 3 branches: • Posterior auricular, posterior digastric, stylohyoid
Parotid Anatomy: Vessels • Retromandibular Vein: located within the substance of the gland • External carotid : at the inferior level of the gland, the external carotid divides into the superficial temporal and internal maxillary artery.
Parotid Bed: Deep lobe lies on...14 • V: internal jugular vein • A: external and internal carotid arteries • N: glossopharyngeal N vagus N spinal accesory N hypoglossal N • S: styloid process styloglossus mm stylohyloid mm
Anatomy:Submandibular gland • Located in the submandibular triangle of the neck, inferior & lateral to mylohyoid muscle. • The posterior-superior portion of the gland curves up around the posterior border of the mylohyoid and gives rise to Wharton’s duct.
Anatomy: Submandibular Lymphatics Submandibular gland drains into submandibular nodes.
Anatomy: Submandibular Duct13 • Wharton’s duct passes forward along the superior surface of the mylohyoid adjacent to the lingual nerve. • The nerve winds around the duct, first being lateral, then inferior, and finally medial.
Anatomy: Submandibular duct • 2-4mm in diameter & about 5cm in length. • It opens into the floor of the mouth thru a punctum. • The punctum is a constricted portion of the duct to limit retrograde flow of bacteria-laden oral fluids.
Anatomy: Sublingual glands Lie on the superior surface of the mylohyoid muscle and are separated from the oral cavity by a thin layer of mucosa.
Anatomy: Sublingual glands • The ducts of the sublingual glands are called Bartholin’s ducts. • In most cases, Bartholin’s ducts consists of 8-20 smaller ducts of Rivinus. These ducts are short and small in diameter.
Anatomy: Sublingual glands • The ducts of Rivinis either open… • individually into the FOM near the punctum of Wharton’s duct • on a crest of sublingual mucosa called the plica sublingualis • open directly into Wharton’s duct
Physiology13 • Physiologic control of the SG is almost entirely by the autonomic nervous system; parasympathetic effects predominate. • If parasympathetic innervation is interrupted, glandular atrophy occurs. • Normal saliva is 99.5% water • Normal daily production is 1-1.5L
ObstructiveSalivary Gland Disorders • Sialolithiasis • Mucous retention/extravasation
Obstructive SG Disorders:Sialolithiasis • Sialolithiasis results in a mechanical obstuction of the salivary duct • Is the major cause of unilateral diffuse parotid or submandibular gland swelling2
Sialolithiasis Incidence2 • Escudier & McGurk 1:15-20 0003 • Marchal & Dulgurerov 1:10-20 0002 Sialolithiasis remains the most frequent reason for submandibular gland resection5
Sialolithiasis • The exact pathogenesis of sialolithiasis remains unknown. • Thought to form via…. an initial organic nidus that progressively grows by deposition of layers of inorganic and organic substances. • May eventually obstruct flow of saliva from the gland to the oral cavity.
Sialolithiasis Acute ductal obstruction may occur at meal time when saliva producing is at its maximum, the resultant swelling is sudden and can be painful.
Gradually reduction of the swelling can result but it recurs repeatedly when flow is stimulated. This process may continue until complete obstruction and/or infection occurs.
Etiology2 • Water hardness likelihood? …Maybe…. • Hypercalcemia…in rats only • Xerostomic meds • Tobacco smoking, positive correlation • Smoking has an increased cytotoxic effect on saliva, decreases PMN phagocytic ability and reduces salivary proteins
Etiology7 Gout is the only systemic disease known to cause salivary calculi and these are composed of uric acid.
Stone Composition2 • Organic; often predominate in the center • Glycoproteins • Mucopolysaccarides • Bacteria! • Cellular debris • Inorganic; often in the periphery • Calcium carbonates & calcium phosphates in the form of hydroxyapatite
Parotid (PG) vs. Submandibular Gland (SMG)…. • Most authorities agree obstructive phenomemnon such as mucous plugs and sialoliths are most commonly found in the SMG • Escudier et al3 • Lustmann et al4 • Rice7 • Others note that parotid glands are most commonly affected2
Reasons sialolithiasis may occur more often in the SMG7 • Saliva more alkaline • Higher concentration of calcium and phosphate in the saliva • Higher mucus content • Longer duct • Anti-gravity flow
Other characteristics: • Despite a similar chemical make-up, 80-90% of SMG calculi are radio-opaque7 50-80% of parotid calculi are radiolucent7 • 30% of SMG stones are multiple 60% of Parotid stones are multiple
Clinical presentation10 • Painful swelling (60%) • Painless swelling (30%) • Pain only (12%) • Sometimes described as recurrent salivary colic and spasmodic pains upon eating
Clinical History • History of swellings / change over time? • Trismus? • Pain? • Variation with meals? • Bilateral? • Dry mouth? Dry eyes? • Recent exposure to sick contacts (mumps)? • Radiation history? • Current medications?