Sialadenitis refers to inflammation of the salivary glands. It may be acute or chronic and has a broad range of causes.
Patients may present with painful swelling of the concerned salivary gland, after eating (salivary colic). In bacterial sialadenitis, there may be a purulent discharge.
Sialadenitis can occur in various forms ranging from acute bacterial sialadenitis (acute suppurative sialadenitis) to acute viral sialadenitis to chronic sialadenitis.
Acute sialadenitis is most commonly caused by an ascending bacterial infection, with Staphylococcus aureus or Streptococcus viridans being the most common organisms 2,8,9. Sialolithiasis is often present (causing obstructive sialadenitis) and stones are found in ~85% of submandibular ducts and ~15% of parotid ducts 1,7,9. Other causes of acute sialadenitis include dehydration, immunosuppression, iatrogenic (drug-induced) and rarely hematogenous spread 10. Rarely sialadenitis may be secondary to an obstructive salivary duct carcinoma.
Epidemic parotitis is associated with the mumps virus, occurs mostly in children and is usually bilateral 10.
Other conditions related to sialadenitis include:
- Sjogren syndrome: chronic sialadenitis 2
- Mikulicz syndrome: chronic sialadenitis 2
- post-radiation: post-irradiative sialadenitis 4
- iodine-131 administration 3
- HIV-associated sialadenitis or immune reconstitution inflammatory syndrome (IRIS), often presenting with bilateral parotid swelling 11.
Due to calculi being a dominant etiological factor, the distribution of sialadenitis follows that of sialolithiasis and therefore the submandibular glands are the most commonly affected (approximately 85%) as the submandibular ducts have more of an upward course and the secreted saliva has a higher viscosity 11.
Sialography is contraindicated in acute sialadenitis because it can worsen the infection 2.
In acute sialadenitis, the affected gland appears enlarged, hypoechoic and hyperemic on ultrasound 8,10.
In chronic infective forms, the affected gland appears atrophic and diffusely hypoechoic with irregular margins - the ultrasound appearances have been likened to that of a “cirrhotic” liver 8.
There may be evidence of sialectasis if recurrent.
- enlarged salivary gland with abnormal attenuation, indistinct margin and vivid contrast enhancement with associated adjacent fat stranding and/or thickening of the deep cervical fascia that is typically unilateral 2,9,10
- dilated duct from sialolithiasis or stenosis 9
- enlarged intra- or extra-glandular lymph nodes may also be seen but this is non-specific and can occur in other conditions such as malignancy 2
- abscesses are hypodense fluid collections, which may or may not be loculated 10
The salivary gland(s) is often enlarged. The affected gland can range from well-defined to poorly defined. Signal characteristics in the majority of cases tend to be heterogeneous 6.
Signal characteristics include:
- acute sialadenitis: low signal 10
- chronic sialadenitis: inhomogeneous low signal 10
- acute sialadenitis: overall signal tends to be high 6
- chronic sialadenitis: overall signal may be low-to-intermediate due to fibrosis 6
Treatment and prognosis
Treatment is usually endoscopic or surgical stone removal 11. If stone removal is unsuccessful the duct and gland may need to be removed if symptoms do not resolve.
Differential conditions to keep in mind include 10:
- 1. Ching AS, Ahuja AT, King AD et-al. Comparison of the sonographic features of acalculous and calculous submandibular sialadenitis. J Clin Ultrasound. 29 (6): 332-8. doi:10.1002/jcu.1044 - Pubmed citation
- 2. Yousem DM, Kraut MA, Chalian AA. Major salivary gland imaging. Radiology. 2000;216 (1): 19-29. Radiology (citation) - Pubmed citation
- 3. Choi N, Schularick N, Diggelmann H et-al. Radiology quiz case 1. Iodine 131–induced sialadenitis. Arch. Otolaryngol. Head Neck Surg. 2012;138 (6): 597-8. doi:10.1001/archoto.2012.429 - Pubmed citation
- 4. Shimizu M, Sekine N, Nishimura K et-al. Magnetic resonance imaging of experimentally-induced sialadenitis in rat submandibular glands. Dentomaxillofac Radiol. 1999;28 (6): 330-7. doi:10.1038/sj/dmfr/4600470 - Pubmed citation
- 5. Ching AS, Ahuja AT. High-resolution sonography of the submandibular space: anatomy and abnormalities. AJR Am J Roentgenol. 2002;179 (3): 703-8. AJR Am J Roentgenol (citation) - Pubmed citation
- 6. Kaneda T, Minami M, Ozawa K et-al. MR of the submandibular gland: normal and pathologic states. AJNR Am J Neuroradiol. 1996;17 (8): 1575-81. AJNR Am J Neuroradiol (citation) - Pubmed citation
- 7. Isacsson G, Ahlner B, Lundquist PG. Chronic sialadenitis of the submandibular gland. A retrospective study of 108 case. Arch Otorhinolaryngol. 1981;232 (1): 91-100. - Pubmed citation
- 8. Alyas F, Lewis K, Williams M et-al. Diseases of the submandibular gland as demonstrated using high resolution ultrasound. Br J Radiol. 2005;78 (928): 362-9. doi:10.1259/bjr/93120352 - Pubmed citation
- 9. Capps EF, Kinsella JJ, Gupta M et-al. Emergency imaging assessment of acute, nontraumatic conditions of the head and neck. Radiographics. 2010;30 (5): 1335-52. Radiographics (full text) - doi:10.1148/rg.305105040 - Pubmed citation
- 10. Fritz B. Head and neck imaging. Thieme Georg Verlag. ISBN:3131440813. Read it at Google Books - Find it at Amazon
- 11. Kamalian S, Avery L, Lev M et-al. Nontraumatic Head and Neck Emergencies. (2019) RadioGraphics. 39 (6): 1808-1823. doi:10.1148/rg.2019190159 - Pubmed