Other / Other / MRI

Sialadenitis

Patients present with painful swelling of the salivary gland, often triggered by eating, and may have purulent discharge; the condition may be acute bacterial, viral, or chronic in nature.
Look For First
  • Enlarged salivary gland with vivid contrast enhancement on CT or high T2 signal on MRI
  • Dilated salivary duct with or without visible sialolith
  • Adjacent fat stranding and deep cervical fascia thickening in acute cases
  • Submandibular gland involvement (85% of cases due to duct anatomy and viscous saliva)
Key Image Findings
  • Acute sialadenitis on CT: enlarged salivary gland with abnormal attenuation, indistinct margins, and vivid homogeneous or heterogeneous contrast enhancement typically unilateral.
  • On MRI, acute sialadenitis shows low T1 signal and high T2 signal within the enlarged gland reflecting edema and inflammation.
  • Chronic sialadenitis demonstrates atrophic gland appearance with heterogeneous low T1 signal and low-to-intermediate T2 signal due to fibrosis on MRI.
  • Ultrasound in acute disease reveals enlarged hypoechoic and hyperemic gland; in chronic disease, the atrophic gland appears diffusely hypoechoic with irregular margins resembling a 'cirrhotic' liver.
  • Associated imaging findings include adjacent fat stranding and thickening of the deep cervical fascia in acute cases, reflecting spread of inflammation.
  • Dilated duct (sialectasis) from obstruction by sialoliths or stenosis; submandibular ducts are affected in ~85% of cases due to upward course and viscous secretions.
  • Hypodense fluid collections (abscesses) may be present as a complication, with or without loculation.
  • Intra- or extra-glandular lymph node enlargement is non-specific and may also be seen with other conditions such as malignancy.
Differential Diagnosis
  • Sjögren disease: chronic autoimmune condition with similar imaging of chronic sialadenitis; distinguishing features include systemic symptoms, autoantibodies, and characteristic punctate/globular sialectasis pattern on sialography.
  • Sialadenosis: non-inflammatory parenchymal enlargement without ductal obstruction; typically shows uniform swelling without enhancement and no evidence of infection or obstruction.
  • Sarcoidosis: may cause chronic sialadenitis-like appearance with glandular enlargement; distinguished by presence of non-caseating granulomas on histology and systemic manifestations.
  • Parotid carcinoma with secondary obstruction: may present similarly with obstruction and ductal dilation; requires imaging surveillance for mass lesion and local invasion.
  • Mumps (epidemic parotitis): viral sialadenitis typically bilateral affecting parotid glands, usually in children; self-limited course in contrast to bacterial sialadenitis.
Discussion

Sialolithiasis is a dominant etiological factor in acute sialadenitis, found in approximately 85% of submandibular duct cases; submandibular glands are most commonly affected due to their upward course and higher salivary viscosity.

Acute bacterial sialadenitis is most commonly caused by Staphylococcus aureus or Streptococcus viridans via ascending infection; other causes include dehydration, immunosuppression, and drugs.

Chronic sialadenitis demonstrates progressive fibrosis and atrophy; imaging shows low T2 signal reflecting parenchymal replacement with fibrotic tissue.

Sialography is contraindicated in acute sialadenitis as it may worsen infection; ultrasound and CT are preferred imaging modalities.

Complications of untreated sialadenitis include abscess formation and airway compromise; early diagnosis and treatment via endoscopic or surgical stone removal can prevent morbidity.

HIV-associated sialadenitis and IRIS may present with bilateral parotid swelling, requiring awareness of patient immunostatus in imaging interpretation.

Reporting Pearls

Clearly describe the affected gland by location and size, specify the presence and location of obstruction (dilated duct, sialolith), note the pattern of enhancement (vivid/homogeneous in acute vs. heterogeneous in chronic), document associated findings (fat stranding, fascia thickening, abscess), and comment on lymph node status as non-specific adjunct finding.

Pitfalls
  • Misinterpreting lymph node enlargement as malignancy; nodal changes are non-specific in sialadenitis and can occur in other conditions.
  • Performing sialography in acute sialadenitis, which can worsen infection; ultrasound or CT should be used instead.
  • Overlooking bilateral involvement in cases of viral sialadenitis (mumps) or HIV-associated sialadenitis where presentation may be subtle.
  • Attributing all chronic glandular atrophy and heterogeneous signal to sialadenitis without considering systemic diseases such as Sjögren disease or sarcoidosis.
Source: Reference source

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