Sialolithiasis is the presence of calculi (stones) in the duct of a salivary gland.
Sialolithiasis is a frequent disease of the salivary glands and the most frequent cause of all salivary-duct obstructions.
The prevalence in the general population is around 1%. Demographically, it tends to affect patients between the age of 40-60. The data regarding gender predominance differs in the medical literature. It is rare during childhood, accounting for less than 3% of all sialolithiasis cases.
The submandibular gland is the most commonly affected (80% to 96% of cases), followed by the parotid gland. It is rare event in the sublingual gland and even more infrequently the minor salivary glands.
Most salivary stones are located in the extraparenchymal salivary ducts (Wharton’s and Stensen’s duct) or at the hilum.
The pathogenesis of sialolithiasis is still debated. Stasis of salivary flow is considered to be a major risk factor. This may be the consequence of:
A) Secretory inactivity, as a result of:
B) Ductal stenosis, polyps, invagination
C) Ductal muscle malfunction
When the saliva stagnates, the high concentration of calcium in the large ducts tends to precipitate.
Stasis also allows bacteria to move through the salivary ducts, shifting salivary pH and promoting calculus formation.
Once a calculi has formed, its impaction in the salivary ducts further obstructs the flow of saliva and the consequent tissue compression leads to atrophy, fibrosis and over time ductal stenosis, leading to further salivary stasis.
The submandibular gland is more prone to salivary stasis and lithiasis due to its:
A) Anatomical features: Saliva from the submandibular gland flows against gravity and Wharton’s duct is longer and larger in comparison with Stensen’s duct (parotid).
B) Physiological features: submandibular gland saliva is more viscous, with an alkaline pH and a higher concentration of calcium, phosphate and mucin.
On the other hand, sublingual and minor salivary glands are less affected due to their spontaneous secretion in the absence of central nervous stimuli, which prevents stasis.
Usually, there are calcified peripheral lamellae, surrounding a core composed of mineral and organic material in variable proportions.
The most frequent mineral is hydroxyapatite. Organic components are usually condensed decomposed salivary gland secretory material.
Most sialolitihs pass asymptomatically.
However of those that don't, the classical presentation of obstruction of the main salivary gland duct is of intermittent swelling of the gland that increases during meals and then wanes out after. This is due to increased saliva production whilst eating.
In the case of gland infection, patients present with a painful permanently swollen gland. (Please refer to the salivary gland swellings article and search for the topic “acute suppurative parotitis”).
Computer tomography (CT) scan is the most reliable and revealing imaging study for calculi detection. Radiographs and ultrasound (US) are also helpful. A sialolith appears as a hyperechoic mass with posterior shadowing in US and hyperdense mass in a CT scan.
CT scan sagittal, coronal and transverse cuts, showing a swallon left submandibular gland, with an intraglandular sialolith measuring 17*12 millimetres.
Choosing the most adequate invasive technique depends on stone location, size and mobility.
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Chung, M., et al. 2007. Pediatric Sialolithiasis: What is different from adult sialolithiasis? International journal of pediatric otorhinolaryngology. 2007, Vol. 71, pp. 787-791.
Austin, T., Davis, J. and Chan, T. 2004. Sialolithiasis of submandibular gland. Visual diagnosis in emergency medicine. 2004, Vol. 26, 2, pp. 221-223.
Jardim, E., et al. 2011. Sialolithiasis of the submandibular gland. The Journal of Craniofacial Surgery. 2011, Vol. 22.
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