32.3 Obstructive and Reactive Salivary Gland Disease
Key Takeaways
- Submandibular stones predominate because the duct runs upward against gravity and the saliva is more mucinous, more alkaline and richer in calcium and phosphate.
- Mealtime syndrome is pain and swelling on eating that subsides over one to two hours as saliva slowly drains.
- About 80% of mucoceles are mucus extravasation phenomena of the lower labial mucosa, lined by granulation tissue rather than epithelium.
- A ranula is a mucocele of the floor of the mouth arising from the sublingual gland; a plunging ranula extends through mylohyoid into the neck.
- Necrotising sialometaplasia mimics malignancy clinically but is self-limiting and resolves over six to ten weeks.
Salivary Gland Pathology
Obstructive and Reactive Salivary Disorders
Obstructive Salivary Conditions
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Sialolithiasis Mucoceles Ranula
• 80-90% Submandibular (Wharton's) • Lower lip predilection • Sublingual gland origin
• Uphill anti-gravity flow • Extravasation: Trauma, pseudocyst • Floor of mouth swelling
• Alkaline, viscous mucin • Retention: Ductal obstruction, true • "Plunging": Dissects
• Mealtime colicky swelling / pain • Granulation wall with foamy macrophages through mylohyoid muscle
1. Sialolithiasis (Salivary Calculi / Stones)
- Etiology: Calcified organic-inorganic concretions that form within the salivary ductal system. Inorganic core is predominantly calcium phosphate (hydroxyapatite) and calcium carbonate deposited around a central organic nidus of desquamated epithelial cells and bacteria.
- Site Predilection: 80% to 90% occur in the submandibular gland (Wharton's duct); 10% to 15% in the parotid (Stensen's duct); <2% in sublingual/minor glands.
- Why is Wharton's Duct Predominantly Affected? (Key Examination Concept):
- Anatomy: Wharton's duct is long (5 cm), wide, and courses upward against gravity from the posterior submandibular gland to the sublingual caruncle, promoting salivary stasis.
- Salivary Characteristics: Submandibular saliva has a higher mucin content (thick, viscous) compared to the purely serous secretions of the parotid gland.
- Chemical Composition: Submandibular saliva is more alkaline (higher pH) and possesses a higher concentration of calcium and phosphate ions, which heavily favors mineral precipitation.
- Clinical Presentation: Recurrent, sudden, cramp-like, colicky pain and rapid tense swelling of the affected submandibular gland provoked immediately by the anticipation, sight, smell, or consumption of food ("Mealtime Syndrome"). Obstruction blocks outflow; swelling subsides over 1–2 hours as saliva slowly drains.
- Imaging: Mandibular standard lower occlusal radiographs readily demonstrate radiopaque calculi within Wharton's duct (approximately 80% of submandibular stones are radiopaque; in contrast, only 20% of parotid stones are radiopaque, requiring sialography, ultrasound, or CT).
2. Mucoceles (Mucus Extravasation vs Retention Phenomenon)
- Mucus Extravasation Phenomenon: Represents over 80% of all mucoceles. Caused by mechanical trauma (e.g., lower lip biting) that severs or lacerates a minor salivary duct, resulting in the spillage (extravasation) of mucin into the surrounding submucosal connective tissue.
- Site: Almost exclusively located on the lower labial mucosa (vermilion border). Mucoceles are exceptionally rare on the upper lip; any swelling of the upper lip must be considered a salivary neoplasm until proven otherwise.
- Clinical Presentation: Painless, fluctuant, dome-shaped, compressible, bluish-translucent submucosal vesicle or nodule that characteristically ruptures, collapses, and refills.
- Histopathology: A pseudocyst lacking an epithelial lining. Composed of an extravasated pool of mucin encircled by a fibrous wall of vascular granulation tissue heavily infiltrated by foamy, lipid-laden macrophages (muciphages).
- Mucus Retention Cyst: True cyst lined by ductal epithelium (cuboidal, columnar, or squamoid). Caused by partial ductal obstruction (micro-calculus or periductal scar tissue) resulting in ductal dilation.
3. Ranula & Plunging Ranula
- Ranula: A large, bluish, translucent, dome-shaped extravasation mucocele occurring specifically in the floor of the mouth, arising from damage to the main duct (duct of Bartholin) or minor ducts (ducts of Rivinus) of the sublingual salivary gland. Named from rana (Latin for frog) due to its resemblance to a frog's translucent underbelly. Displaces the tongue superiorly and medially.
- Plunging (Cervical) Ranula: Occurs when extravasated mucin dissects inferiorly through or around the posterior free border of the mylohyoid muscle (or through a congenital defect: the mylohyoid boutonnière) into the submandibular and parapharyngeal fascial spaces of the neck. Presents as a soft, painless, fluctuant, non-pulsatile cervical mass in the neck without an obvious intraoral component. Treatment requires surgical excision of the underlying offending sublingual salivary gland via an intraoral approach.
Investigating a Salivary Swelling
The diagnostic reasoning depends on the time course of the swelling, and this is what examiners test. A swelling that appears at mealtimes and subsides afterwards is obstructive, and the likely cause is a sialolith or a duct stricture. A swelling that is acute, painful, tender and associated with pus at the duct orifice is acute bacterial sialadenitis, typically ascending infection in a dehydrated or xerostomic patient. A swelling that is persistent, painless, firm and progressive is a neoplasm until proven otherwise. Bilateral, painless, symmetrical enlargement suggests sialosis, associated with diabetes, alcohol dependence, bulimia, malnutrition and acromegaly, or a systemic condition such as Sjögren's syndrome or sarcoidosis.
Investigations and Their Indications
Around 80 per cent of salivary calculi occur in the submandibular gland, because its secretion is more mucoid and alkaline and its duct runs uphill against gravity; most submandibular stones are radiopaque and visible on a lower true occlusal radiograph. Parotid stones are more often radiolucent. Ultrasound is the usual first-line imaging for a salivary swelling in the UK. Sialography demonstrates ductal anatomy but is contraindicated during acute infection. Sialendoscopy allows both diagnosis and minimally invasive stone retrieval. Fine needle aspiration cytology is used for a suspected neoplasm; incisional biopsy of a parotid mass is avoided because of the risks of facial nerve injury and tumour seeding.
Conservative management of a symptomatic stone is worth stating: hydration, gland massage towards the orifice, sialogogues such as citrus or sugar-free chewing gum, warm compresses and analgesia, with intervention if symptoms persist. Mucoceles on the lower lip are extravasation phenomena from minor gland trauma and are excised with the associated minor glands; a ranula in the floor of mouth arises from the sublingual gland, and a plunging ranula extending through mylohyoid requires specialist management.