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Imaging of salivary glands

¹ Radiology Department, St Bartholomew's Hospital, West Smithfield, London EC1A 7BE, ² Oral and Maxillofacial Radiology, Dental Institute, The Royal London Hospital, Whitechapel, London E1 1BB, UK

Correspondence: Dr S H Liyanage, Specialist Registrar Radiology. E-mail: sidliyanage{at}googlemail.com

• Ultrasound is the investigation of choice for major salivary gland disease, reserving other techniques for further assessment in the minority of cases.
  
• Sialolithiasis is the most common salivary gland pathology, affecting the submandibular ducts in 80% of cases. Digital subtraction sialography is indicated when ultrasound is inconclusive or normal despite a convincing clinical history. Mobile calculi <7 mm in size are amenable to image guided endoluminal extraction. Strictures may undergo endoluminal balloon dilatation.
  
• Diffuse multiglandular parenchymal disease is non-specific and can be caused by viral sialadenitis, Sjögren's syndrome, sarcoidosis or benign lymphoepithelial cysts in HIV.
  
• There is an increased risk of mucosa-associated lymphoid tissue (MALT) lymphoma of the salivary glands in Sjögren's syndrome and any dominant mass should be biopsied.
  
• A ranula is said to be plunging when it extends into the submental or submandibular triangles following rupture.
  
• All solitary salivary gland masses are neoplastic until proved otherwise and require fine needle aspiration (FNA).
  
• Whenever malignancy is discovered, MRI should be performed to assess soft tissue invasion and perineural spread.
  
• MRI is the investigation of choice for minor salivary gland disease as a high proportion of tumours are malignant.
  

The salivary glands are divided into major and minor groups. There are three pairs of major salivary glands: parotid, submandibular and sublingual. Numerous small minor salivary glands are found throughout the aero-digestive tract of the neck, including the paranasal sinuses and parapharyngeal space. Both major and minor salivary glands are susceptible to a range of diseases of which sialolithiasis is now the most common in the UK. Imaging modalities used to assess major salivary glands include MRI, CT, digital subtraction sialography (DSS) and ultrasound with or without fine needle aspiration (FNA) or core biopsy, although the exact strategy will vary depending on local resources and expertise. Minor salivary gland disease requires CT or MRI. The aim of this paper is to review the common pathologies to affect both major and minor salivary glands and to describe their typical appearances on imaging.