Introduction
Sialolithiasis is the presence of calculi in the salivary glands or ducts. Stones will form in the salivary gland or ducts following the stagnation of saliva; they are typically composed of calcium phosphate and hydroxyapatite, as the saliva is rich in calcium
They have an incidence of approximately 27-59 cases per million population per year. Whilst most cases are asymptomatic, some can present with facial swelling and / or facial pain.
Salivary Gland Anatomy
The three major salivary glands (Fig. 1) are:
- Parotid gland – located superior to the angle of the mandible, the gland is superficial to the masseter muscle and drains (via Stensen’s duct) opposite to the upper second molar
- Submandibular gland – lying beneath the floor of the mouth in the submandibular triangle, it drains (via Wharton’s duct) into the floor of the mouth, beside the frenulum of the tongue
- Sublingual gland – located below the mucous membrane of the floor of the mouth, they are drained by multiple small ducts that empty either into Wharton’s duct or directly into the floor of the mouth
Figure 1 – The three major salivary glands, the parotid, submandibular, and sublingual glands
Sialolithiasis most commonly occur in the submandibular gland, due to the anatomy of this duct being long and its flow of saliva against gravity. The type of salivary secretions from the submandibular gland are also more mucoid in nature as opposed to the more serous secretions from the parotid gland.
Risk Factors
- Medication, commonly diuretics or anti-cholinergics
- Dehydration
- Gout
- Smoking
- Chronic periodontal disease
- Hyperparathyroidism
Clinical Features
Figure 2 – A stone seen located in the submandibular salivary duct
Individuals with sialolithiasis tend to be asymptomatic, however a small proportion can have an intermittent facial swelling associated with eating, which can be painful or painless. Symptoms are usually unilateral in nature.
When the gland is palpated, saliva can be seen at the duct orifice (Fig. 2), along with the presence of small stones. On palpation, a stone may be palpable in the duct and the gland may feel tender in the presence of infection.
Differential Diagnosis
The main differential to consider for such a presentation is infection. Individuals with viral infection such as mumps will present acutely with pain and swelling of both salivary glands, associated with the viral prodrome fever, malaise, headache, and myalgia.
Other causes of swollen salivary glands include Sjögren’s syndrome, sarcoidosis, or salivary gland tumour (unilateral swelling).
Investigations
Most cases of suspected sialolithiasis are investigated* with either ultrasound or radiographs.
Ultrasound scans are a cheap and minimally invasive method that is very good at analysing the whole gland and periglandular structures. As most salivary gland stones are radio-opaque (80% submandibular gland, 60% parotid gland), a plain film radiograph is a simple investigation which can be performed to confirm presence of a stone.
*Sialography is not routinely performed due to its invasive nature. The duct is cannulated and radiopaque dye is injected with plain films are taken.
Management
Most patients are managed conservatively with oral hydration, analgesia, and sialologues, such as lemon juice, which promote saliva production. Milking / massaging the gland can help as well.
If the gland becomes infected and the patient develops sialedenitis, then antibiotics are typically indicated.
Definitive Management
Patients with recurrent or persistent symptoms should be referred for specialist treatment. Interventional radiology procedures are most commonly trialled, which involve fluoroscopic control such that the stones are visualised in the duct and then extracted with a basket.
A surgical approach can be used to remove some more difficult stones; a transoral approach can be used if the stones are distal or a transcervical approach for proximal stones (or where the transoral approach has been unsuccessful). Surgical intervention however comes with risks of damage to the hypoglossal, facial, or lingual nerves.
Other possible interventions include sialoendoscopy (whereby the stones are directly visualised via endoscopic imaging and extracted with a basket) or extracorporeal shockwave lithotripsy (for some stones in the proximal ducts, where transoral retrieval of the stone is not possible).
Gland removal is last resort. Excision of the parotid or submandibular gland are only performed for patients with chronically persisting symptoms.
Complications
Most patients with salivary calculi will live with them for several years, many developing recurrent infections and in some patients chronic sialedenitis resulting in a chronically tender salivary gland. Severe cases of infection can also result in abscess formation.
Key Points
- Sialolithiasis is the presence of calculi in the salivary glands or ducts
- Most cases are asymptomatic yet some may present with unilateral face swelling, typically worse with eating
- Most cases of suspected sialolithiasis are investigated with either ultrasound or radiographs
- Conservative management is all that is required for most cases, however surgical and radiological interventions may be required in a minority
