Sialolithiasis is a benign (non-malignant) condition involving the formation of stones within the ducts of the major salivary glands of the head and neck. These include the parotid glands, submandibular glands, and sublingual glands. Sialolithiasis is the most common cause of salivary gland swelling with a reported incidence of 1 in 10000 to 1 in 30000. Sialolithiasis can result in obstruction of the major salivary gland ducts, which can lead to inflammation from destructive salivary enzymes, superimposed bacterial infection termed sialadenitis, or in rare cases abscess formation. There is a variety of presenting symptoms, with the most common being cyclical postprandial swelling of the major salivary glands and decreased saliva production. In the case of larger salivary stones involving the distal submandibular duct (Wharton’s duct), diagnosis is often possible based on physical examination. Cases involving smaller stones within the distal submandibular duct or parotid duct (Stenson’s duct) were historically diagnosed utilizing conventional radiography, sialography, and digital subtraction sialography. Modern diagnostic techniques involve point-of-care ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), and direct visualization with sialoendoscopy. A variety of treatment options exist for sialolithiasis including medications termed sialogogues, direct massage of distal stones out of the duct, and a variety of procedures including interventional sialography, lithotripsy, sialoendoscopy, and various surgeries.
Factors affecting salivary stone formation are not well understood. Research into etiologic factors remains limited due to the relatively rare incidence of the disease, which makes extensive studies difficult. In general, etiologic factors believed to affect salivary stone formation divide into two major groups, anatomical factors affecting saliva formation or flow (i.e., duct stenosis or inflammation) and composition factors (i.e., increased calcium content or altered enzyme function). Research examining the geographic distribution of hard water and salivary calculi formation demonstrated no correlation with an increased incidence of salivary stone formation in areas of increased water hardness. Studies examining the effects of hypercalcemia using animal models demonstrated no evidence of increased salivary stone formation with hypercalcemia. Additional factors such as decreased fluid intake and pharmacologic side effects resulting in decreased salivary production (i.e., diuretic use); however, research in these areas remains limited. In recent years tobacco smoking has been discussed as a potential risk factor for the formation of salivary stones. Proposed mechanisms include the development of inflammation within the salivary ducts and decreased production of salivary amylase.
The incidence of sialolithiasis is estimated at 1 in 10000 to 1 in 30000 individuals. The primary age at diagnosis is between 30 to 60 years old, and there is a higher incidence in males. Approximately 85% of stones occur within the submandibular gland due to a variety of factors, making it the most common location for sialolithiasis. One such factor is that the submandibular duct ascends towards its opening in the oral cavity, which can result in a stagnant flow of saliva. Additionally, the submandibular gland produces predominately mucinous saliva, which is more viscous than the secretions created by the parotid gland, resulting in a more stagnant flow of secretions. The submandibular gland also produces more alkaline saliva, which predisposes to precipitation of inorganic salts (i.e., calcium and phosphate), which further predisposes to salivary stone formation. Approximately 15% of salivary stones occur within the parotid gland, and less than 5% occur within the sublingual and minor salivary glands.
The exact pathogenesis of sialolithiasis is not well understood, with two dominant theories suggested regarding their formation. One theory suggests that there are multiple internal microcalculi within salivary gland secretory granules. When these microcalculi get secreted into the salivary ducts, they may act as a nidus for the formation of larger calculi, ultimately forming a sialolith. Another proposed hypothesis suggests bacteria or food debris within the oral cavity may enter the distal submandibular or parotid ducts. Over time, this organic substrate may act as a nidus for the formation of larger calculi.
Histologically, sialoliths are composed of varying ratios of organic and inorganic materials within an inner core. The inner core is considered the initial sialolith, which subsequently enlarges from the deposition of additional organic and inorganic material, forming the outer lamellae (layers). Inorganic materials include hydroxyapatite, whitlockite, and octacalcium phosphate, with hydroxyapatite being the most prevalent. The exact ratios of inorganic material found within a sialolith depend on the chemical environment in which it forms. Organic materials found within sialoliths include glycoproteins, cellular debris, bacteria, and mucopolysaccharides. Studies utilizing scanning electron microscopy (SEM) and polymerase chain reaction (PCR) have demonstrated the presence of bacteria within sialoliths, predominantly the Streptococcus genus. Bacteria are not present in all sialoliths suggesting they are not necessary for their formation.
Clinical diagnosis of sialolithiasis can be challenging as patients may not be symptomatic unless the stone results in obstruction of the salivary ducts, termed sialadenitis. Patients with obstructing stones will commonly present with a history of unilateral salivary gland swelling and acute onset of pain that worsens with meals. The physical exam will demonstrate asymmetric swelling of the affected salivary gland. Approximately 60% of parotid stones and 30% of submandibular stones will be located distally in their respective ducts. If large enough, these stones may be visually apparent on examination of the oral cavity. On visual inspection, salivary stones typically demonstrate an oval or round shape and a white or yellow color. If not visually apparent, the stones are usually palpable along the anatomic course of the affected salivary duct/gland.
There are a variety of radiographic tests with utility for the diagnosis of sialolithiasis. Historically, conventional radiographs utilizing occlusal views were the initial diagnostic choice. These demonstrated large radiopaque ductal stones well. However, they missed smaller stones and were insensitive to parenchymal stones. Additionally, only around 80% of stones are radioopaque, which leads to a large number of stones not being diagnosed. While conventional radiography can still be useful in the initial workup of salivary stones, modern imaging techniques using ultrasound or CT can provide better sensitivity for diagnosis as well as localization information.
Sialography is historically regarded as the gold standard for the diagnosis of sialolithiasis as it allows for excellent visualization of the salivary ducts and underlying ductal pathology. Using this technique, contrast injected via small needle allows radiographic visualization and acts as a sialogogue and can be therapeutic, allowing passage of smaller stones. Disadvantages include radiation exposure (mainly if using digital is utilized) and risk of contrast reaction.
Non-contrast computed tomography (NCCT) is a widely used modality for the evaluation of sialolithiasis. Advantages include excellent sensitivity and specificity for calcified stones, fast acquisition time, and widespread availability. Disadvantages include radiation exposure and limited evaluation of the ductal system or underlying pathology (i.e., obstructing masses). The administration of intravenous contrast has historically been utilized only as an adjunct to NCCT due to concerns small vessels may simulate calcifications resulting in false-positive results. A recent study in the American Journal of Neuroradiology comparing contrast-enhanced CT (CECT) and NCCT demonstrated excellent sensitivity and specificity with no false-positive results. Benefits of initial CECT include better evaluation of the ductal system, improved soft-tissue contrast in the assessment of salivary masses, and decreased radiation dose (compared to dual-phase NCCT with CECT).
MR Sialography demonstrates similar sensitivity and specificity to NCCT for the evaluation of sialolithiasis. Benefits of MR include excellent visualization of the salivary ducts without the need for contrast and no radiation exposure. Disadvantages include cost, image acquisition time, and limited availability compared to NCCT and Ultrasonography.
Sialendoscopy allows for direct visualization of salivary stones and the salivary ducts, thus providing excellent sensitivity and specificity. In addition to aiding in the diagnosis of sialolithiasis, clinicians increasingly use sialoendoscopy for therapy and stone removal, given advancements in endoscopic technology. Research has shown sialoendoscopy to be a safe and effective alternative to conventional open surgical techniques with a more favorable complication profile. Additionally, sialoendoscopy is performable in the outpatient setting utilizing local anesthesia.
Ultrasonography provides a noninvasive method of imaging sialolithiasis. The usual appearance of sialoliths utilizing ultrasound is a hyperechoic focus with posterior shadowing. Benefits to ultrasonography include no radiation exposure, real-time image interpretation, and widespread availability. Ultrasound is often available at point of care and can provide rapid diagnostic information to dictate further management. Ultrasound is highly operator dependent, which is supported when reviewing the literature, which reveals a wide range of reported sensitivity and specificity. Reported sensitivities are best for stones greater than 2 to 3 mm in size, and recent research has demonstrated sensitivity and specificity for stones greater than 3 mm in size comparable to conventional NCCT and sialoendoscopy.
Management of sialolithiasis should begin with conservative measures including massage of the salivary gland, nonsteroidal anti-inflammatory drugs (NSAIDs), and sialogogues. Signs of infection, including cervical adenopathy, purulent discharge from the salivary ducts, or erythema surrounding the salivary ducts, indicate the need for antibiotic therapy.
If conservative management is unsuccessful, further treatment is dictated based on the size, number, and location of the sialolith.
Mobile submandibular stones measuring less than 5 mm and located within the distal duct should initially undergo management with endoscopy. Impacted submandibular stones within the distal duct and stones larger than 5 mm should have treatment with transoral duct slitting. Stones within the proximal duct or hilar region that are 5 to 7 mm should receive initial treatment endoscopically. If this is unsuccessful or the stone becomes impacted, the next step is a transoral surgical approach. External shockwave lithotripsy (ESWL) is an option for stones that are not palpable or not visualized under endoscopy. Intraparenchymal stones can be extracted endoscopically if they are 5 to 7 mm and visualized. Larger stones require treatment with transoral slitting. ESWL is indicated for smaller stones that are not palpable and not visualized endoscopically. ESWL is generally unsuccessful for stones larger than 7 to 10 mm. Surgical excision of the submandibular gland should be a last resort.
Salivary stones within the parotid duct that measure less than 7 mm and are mobile requires endoscopic removal. If endoscopic management is unsuccessful or the stones have become impacted, ESWL is considered the most appropriate second-line therapy with subsequent endoscopic removal of fragmented stones. Treatment of salivary stones that do not respond to ESWL is with a combined transcutaneous and endoscopic approach (assuming the stone is visible under endoscopy). Surgical excision of the parotid gland should be a last resort.
The differential diagnosis for salivary gland swelling includes:
However, the clinical presentation can vary, and the differential diagnosis for the pathology of the oral cavity and face can be extensive and relies heavily on physical exam findings and clinical history. Conditions that can have a similar presentation include:
Sialolithiasis has an excellent prognosis, and the majority of patients can be managed conservatively with sialogogues and NSAIDs. The minimally invasive procedures discussed above have excellent success rates with minimal morbidity in comparison to traditional surgical techniques. Sialadenectomy for the treatment of sialolithiasis is rarely necessary with modern treatment techniques.
The primary complications of sialolithiasis are the development of sialadenitis (acute or chronic) and atrophy of the affected salivary gland. Obstruction of the salivary glands by a sialolith blocks the flow of saliva resulting in swelling and pain. Additionally, this blockage of flow prevents the removal of bacteria and debris from the salivary duct, which can result in bacterial infection. If the obstruction is chronic, the blocked flow of saliva will damage the acinar cells of the salivary glands resulting in local inflammation. Without proper treatment, it can result in permanent fibrosis of the gland and atrophy.
Patients should be informed sialolithiasis has an excellent prognosis and most cases resolve with conservative management. Patients require education on common initial symptoms such as glandular swelling and pain with meals that might suggest they have formed a new sialolith. While sialolithiasis is usually idiopathic, the formation of stones can be secondary to an obstructing process such as ductal stenosis or neoplasm. Patients need to understand that they should inform their clinician of recurrent or worsening symptoms that would indicate a need for more advanced imaging workup or referral to a head and neck specialist.
Sialolithiasis is the most common benign cause of salivary gland swelling; however, it remains a relatively rare diagnosis with an incidence of 1 in 10000 to 1 in 30000. The disease commonly gets diagnosed in the primary care or emergency medicine setting where initial patient contact is mostly with nurses, nurse practitioners, physician assistants, primary care physicians, and emergency medicine physicians. Given the oral nature of the disease, some patients may initially present to their dentist for evaluation of symptoms. Diagnostic radiologists are often involved in the initial workup for imaging recommendations and interpretation. The potential involvement of all these disciplines is why an interprofessional team approach is necessary for the diagnosis and management of this condition.
An interprofessional approach and open communication among providers can aid in ensuring patients receive appropriate initial management resulting in a quicker resolution of symptoms. Open communication among the radiologist and primary care provider can help aid in timely referral to an otolaryngologist when a large sialolith is present that is likely to fail conservative measures. Additionally, patients should be educated to inform their provider if symptoms are not improving or are worsening, indicating failure of conservative measures and the potential need for referral to an otolaryngologist for advanced interventions. Well-informed nursing staff can assist in the management, and provide patients with assurance that with modern multimodal treatment algorithms, success rates approach 100%, and gland removal is rarely necessary, especially with interprofessional team collaboration. [Level 5]
|||Huoh KC,Eisele DW, Etiologic factors in sialolithiasis. Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery. 2011 Dec; [PubMed PMID: 21753035]|
|||Rzymska-Grala I,Stopa Z,Grala B,Gołębiowski M,Wanyura H,Zuchowska A,Sawicka M,Zmorzyński M, Salivary gland calculi - contemporary methods of imaging. Polish journal of radiology. 2010 Jul; [PubMed PMID: 22802788]|
|||Marchal F,Dulguerov P, Sialolithiasis management: the state of the art. Archives of otolaryngology--head [PubMed PMID: 12975267]|
|||Diebold S,Overbeck M, Soft Tissue Disorders of the Mouth. Emergency medicine clinics of North America. 2019 Feb; [PubMed PMID: 30454780]|
|||Sherman JA,McGurk M, Lack of correlation between water hardness and salivary calculi in England. The British journal of oral [PubMed PMID: 10783448]|
|||Andretta M,Tregnaghi A,Prosenikliev V,Staffieri A, Current opinions in sialolithiasis diagnosis and treatment. Acta otorhinolaryngologica Italica : organo ufficiale della Societa italiana di otorinolaringologia e chirurgia cervico-facciale. 2005 Jun; [PubMed PMID: 16450768]|
|||Harrison JD, Causes, natural history, and incidence of salivary stones and obstructions. Otolaryngologic clinics of North America. 2009 Dec; [PubMed PMID: 19962002]|
|||Marchal F,Kurt AM,Dulguerov P,Lehmann W, Retrograde theory in sialolithiasis formation. Archives of otolaryngology--head [PubMed PMID: 11177017]|
|||Teymoortash A,Wollstein AC,Lippert BM,Peldszus R,Werner JA, Bacteria and pathogenesis of human salivary calculus. Acta oto-laryngologica. 2002 Mar; [PubMed PMID: 11936916]|
|||Brady JM,McKinney L,Stanback JS, Scanning electron microscopy of submandibular sialoliths: a preliminary report. Dento maxillo facial radiology. 1989 Feb; [PubMed PMID: 2599240]|
|||Koch M,Zenk J,Iro H, Algorithms for treatment of salivary gland obstructions. Otolaryngologic clinics of North America. 2009 Dec; [PubMed PMID: 19962014]|
|||Arifa SP,Christopher PJ,Kumar S,Kengasubbiah S,Shenoy V, Sialolithiasis of the Submandibular Gland: Report of Cases. Cureus. 2019 Mar 6; [PubMed PMID: 31106080]|
|||Pachisia S,Mandal G,Sahu S,Ghosh S, Submandibular sialolithiasis: A series of three case reports with review of literature. Clinics and practice. 2019 Jan 29; [PubMed PMID: 30996853]|
|||Terraz S,Poletti PA,Dulguerov P,Dfouni N,Becker CD,Marchal F,Becker M, How reliable is sonography in the assessment of sialolithiasis? AJR. American journal of roentgenology. 2013 Jul; [PubMed PMID: 23789681]|
|||Purcell YM,Kavanagh RG,Cahalane AM,Carroll AG,Khoo SG,Killeen RP, The Diagnostic Accuracy of Contrast-Enhanced CT of the Neck for the Investigation of Sialolithiasis. AJNR. American journal of neuroradiology. 2017 Nov; [PubMed PMID: 28838906]|
|||Strychowsky JE,Sommer DD,Gupta MK,Cohen N,Nahlieli O, Sialendoscopy for the management of obstructive salivary gland disease: a systematic review and meta-analysis. Archives of otolaryngology--head [PubMed PMID: 22710505]|
|||Goncalves M,Schapher M,Iro H,Wuest W,Mantsopoulos K,Koch M, Value of Sonography in the Diagnosis of Sialolithiasis: Comparison With the Reference Standard of Direct Stone Identification. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 2017 Nov; [PubMed PMID: 28556090]|
|||Park HS,Pae SY,Kim KY,Chung SM,Kim HS, Intraoral removal of stones in the proximal submandibular duct: usefulness of a surgical landmark for the hilum. The Laryngoscope. 2013 Apr; [PubMed PMID: 23168610]|
|||Capaccio P,Torretta S,Pignataro L, The role of adenectomy for salivary gland obstructions in the era of sialendoscopy and lithotripsy. Otolaryngologic clinics of North America. 2009 Dec; [PubMed PMID: 19962013]|
|||Capaccio P,Torretta S,Pignataro L, Extracorporeal lithotripsy techniques for salivary stones. Otolaryngologic clinics of North America. 2009 Dec; [PubMed PMID: 19962012]|