Sialolithiasis
Introduction
A sialolith is a calcified stone within the salivary ducts. The sialolith is formed of an organic nucleus, surrounded by concentric layers of calcium phosphate crystals.
In horses the salivary gland involved is usually the parotid gland, and sialoliths usually obstruct the major duct close to the parotid papilla.
In chronic cases, the stone builds up gradually and the duct is only partially obstructed. When obstruction is acute and total, the gland may become painfully inflamed and the duct may rupture.
Pathogenesis
An ascending foreign body, such as a grass awn, is normally the cause of the formation of a single sialolith within a salivary duct. Calcium carbonate can also be deposited around a nidus created by inflammatory cells within the duct.
In small animals, calcification of inspissated saliva in salivary mucoceles may also result in the formation of multiple small sialoliths.
A single, large sialolith in a salivary duct can cause some retention of saliva, however it is not thought to cause a salivary mucocele.
Clinical Signs
A sialolith presents clinically as a palpable elongated swelling over the affected salivary duct.
Radiographic or ultrasonographic examination of the affected salivary gland (most often the parotid gland) may be useful to identify any internal swelling or inflammation.
If the obstruction is acute and complete, the salivary gland may swell, and there may be rupture of the duct and formation of a fistula. There will then be a visible lesion with saliva discharging from the wound.
Treatment
Some sialoliths can be removed from the salivary duct opening using forceps.
If this is not possible, treatment involves direct surgical incision onto the calculus and removal of the stone.
Complications include the formation of a parotid duct fistula after surgery.
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References
Verstraete, F. J. M. (1998) Self-Assessment Colour Review - Veterinary Dentistry Manson
Knottenbelt, D. (2003) Diseases and disorders of the horse Elsevier Health Sciences
Mair, T. (1998) Equine Medicine, Surgery and Reproduction Elsevier Health Sciences
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