Monday 18 March 2013
The formation of salivary gland calculi occurs in the submandibular gland approximately 80 to 90% of the time and in the parotid gland the remaining 10 to 20%.
The sublingual and minor salivary glands are rarely involved. Stone formation is thought to be more common in the submandibular gland secondary to the higher mucin content of its saliva and the anti-gravity flow of saliva within the duct. Its saliva is also more alkaline and has a higher calcium and phosphorous content.
Submandibular stones are usually also larger in size. Serum calcium and phosphorous levels have no known correlation with the formation of calculi. Calculi may be found within the ductal system itself or within salivary gland parenchyma. In most cases of sialolithiasis, a single calculus is involved.
Stone formation occurs via the deposition of calcium phosphate and an organic matrix of carbohydrates and amino acids about a nidus of debris or other material. With the occurrence of ductal obstruction, stasis of saliva may occur with varying degrees of surrounding inflammation and possible ascending bacterial infection. Streptococcus viridans is a common offending pathogen.
Stone formation most often occurs in middle-aged males and may result in intermittent salivary gland swelling and discomfort, especially with eating. Calculi have been associated with the existence of chronic sialadenitis and may present as an acute suppurative sialadenitis.
During an episode of obstruction complicated by acute infection, mucopurulent material may be expressed from the duct orifice with massage of the involved gland. Gout is the only systemic illness associated with the formation of calculi, and these are composed of uric acid. Plain radiograpy (e.g. submentovertex or occlusal films) is occasionally useful in the diagnosis and location of calculi. 90% of submandibular calculi are radiopaque while 90% of parotid calculi are radiolucent.
Sialography is very accurate in the diagnosis of sialolithiasis but is most often unnecessary.
Sialolithiasis may also result in subsequent ductal ectasia and stricture formation.
Smaller stones may pass spontaneously with appropriate conservative management including adequate hydration, sialogogues, heat, massage, and appropriate antibiotics for intercurrent infection.
Stone removal may be performed transorally for those calculi located distally within the duct. However, adequate removal of those calculi located near the hilum of the gland often require complete excision of the involved gland.