Sialolithiasis: Causes, Symptoms, and Diagnostic Approaches

Overview
Sialolithiasis refers to the formation of calcified masses—known as salivary stones or sialoliths—within the ducts of the major salivary glands. These stones obstruct saliva flow, often causing swelling, pain, and sometimes infection of the affected gland. While many cases are asymptomatic, sialolithiasis remains the most common cause of salivary gland obstruction in clinical practice.

Etiology and Pathogenesis

Sialoliths are composed of a mix of organic (cellular debris, glycoproteins, mucopolysaccharides) and inorganic substances (calcium carbonates and phosphates). The most commonly identified mineral is hydroxyapatite. Other minerals such as whitlockite and octacalcium phosphate may be present depending on local conditions.

Key Contributing Factors

Sialolith formation is multifactorial and may result from:

• Saliva retention, due to:
  • Ductal abnormalities or inflammation
  • Dehydration
  • Medications (e.g., diuretics, anticholinergics)
• Saliva composition, especially:
  • High calcium levels
  • Low levels of natural crystallization inhibitors like phytate
• Bacterial infection, which raises salivary pH and promotes calcium precipitation
• Secretory inactivity, especially during prolonged periods without food stimulation
• Anatomical factors, particularly in the submandibular gland

Although not conclusively proven, smoking, high dietary calcium intake, and hyperparathyroidism have been associated with an increased risk of developing salivary stones. Some studies suggest a potential link between sialolithiasis and kidney stones.

Prevalence and Gland Involvement

Sialolithiasis is more common in:

• Submandibular gland (80–90%)
• Parotid gland (5–15%)
• Sublingual and minor glands (2–5%)

The submandibular gland is especially prone due to:

1. The long, curved path of Wharton’s duct
2. High calcium and phosphate content in saliva
3. A dependent (lower) anatomical position promoting stasis
4. Thick, mucous-rich saliva

Stones may develop at any age, including in children, but they are most common in males in their 40s to 50s. Recurrence occurs in approximately 20% of patients.

Mechanism of Stone Formation

Although not fully understood, stone formation likely begins with microcalculi—tiny mineralized deposits formed during periods of reduced salivary flow. Bacteria and debris from the oral cavity may enter the duct and become trapped. Over time, this leads to obstruction, inflammation, and further deposition of calcium-rich material, resulting in lamellar calcification and stone enlargement.

Clinical Features

Common Symptoms

• Pain and swelling during meals (periprandial pain)
• Intermittent gland swelling that resolves after eating
• Tenderness over the affected gland
• Erythema or pus discharge in cases with secondary infection

Signs and Complications

• Unilateral swelling without systemic symptoms is typical in non-infectious cases
• Fistulas, ductal strictures, and gland fibrosis may develop in chronic cases
• Bimanual palpation may reveal the presence of a stone in the duct

Diagnosis

Imaging Modalities

1. Plain Film Radiography
   • Useful for radiopaque stones, especially in the submandibular gland (via 90° occlusal view).
   • Less effective for parotid stones, as many are radiolucent or obscured by anatomy.
2. Conventional Sialography
   • Involves injecting contrast dye to outline the ductal system.
   • Helps differentiate sialoliths from other calcifications (e.g., phleboliths).
   • Contraindicated in acute infections.
3. Ultrasound (US)
   • Non-invasive and widely used.
   • Detects larger or radiolucent stones but may miss small (<2 mm) or multiple stones.
   • Cannot always define precise stone number or location.
4. Computed Tomography (CT)
   • Highly sensitive (10x more than plain radiographs).
   • Best for identifying small or poorly calcified stones.
   • Use of non-contrast CT is preferred to avoid false positives.
5. Cone Beam CT (CBCT)
   • Provides clear ductal visualization with lower radiation than medical CT.
   • Superior to 2D radiography in complex cases.
6. MRI Sialography
   • Non-invasive and free of ionizing radiation or contrast agents.
   • Safe for patients allergic to iodine-based dyes.
   • Contraindicated in patients with pacemakers or claustrophobia.
7. Sialendoscopy
   • Combines diagnosis and treatment in one minimally invasive procedure.
   • A tiny camera is inserted into the duct, allowing real-time visualization and removal of stones.
   • Can be used alongside other imaging methods and followed by ductal stenting to preserve flow.

Conclusion

Sialolithiasis is a common, often underdiagnosed condition of the salivary glands that can lead to significant discomfort and complications if left untreated. Understanding its causes, identifying symptoms early, and selecting the most appropriate imaging method are essential for effective management. With advancements in diagnostic imaging and minimally invasive techniques like sialendoscopy, outcomes for patients with salivary stones have improved significantly