Salivary Gland Swelling

There are many causes of salivary gland swelling. Clinical history and examination are important to determine the most appropriate investigation(s).

It is important to recognise “red flag” features in the history and clinical examination Red Flag features

To summarise the benefits of each imaging modality simply for this pathology:

• Patient age >60
• Rapid growth
• Cutaneous features such as tethering/ulceration
• Facial nerve palsy
• Suspected deep lobe of parotid, or minor gland involvement 
• Cervical lymphadenopathy
• Past medical history of facial/skin cancer 1

• Initial imaging modality of choice in undifferentiated salivary gland swelling.2-5
• Ultrasound can be used to identify:3, 5, 6, 7
  • Ductal dilation
  • Calculi (particularly when ≥ 3mm)
  • Abscess formation
  • Alteration of the normal glandular morphology and differentiate salivary gland lumps due to systemic diseases (e.g. Sjögren’s syndrome vs. IgG4 related dacroadenitis and sialadenitis) 8
  • Mass lesions
• With correlation with appropriate clinical history, diagnosis of the above can often be made with ultrasound alone.3, 5, 6, 7
• In patients with suspected sialolithiasis and with normal sonographic findings, further assessment with conventional or MR sialography is recommended.9
• For mass lesions in the superficial parotid, submandibular and sublingual glands, ultrasound can be used for initial assessment to determine the margins and internal characteristics, and help differentiate malignant from benign neoplasms (sensitivity 52-73%, specificity 89-94%). That is, US may not confidently differentiate benign and malignant masses, and biopsy will be required. It is recommended that further assessment of neoplasms be performed with cross-sectional imaging (MRI) and/or imaging guided fine needle aspiration cytology.2, 3, 10-13
• Ultrasound is of limited utility for imaging the deep lobe of the parotid and for the minor salivary glands.2, 11, 14-16
• If deep tissue extension is suspected or malignancy is confirmed on cytology, either MRI or CT is necessary to evaluate tumour extent, local invasion and perineural spread.7, 16, 17

• Imaging modality of choice when there is a strong suspicion of salivary gland malignancy.2, 16, 18, 19
• MRI can differentiate between inflammatory and neoplastic lesions.20
• MRI has better contrast resolution than CT which allows detailed delineation of tumour margins and accurate local staging. Perineural spread, bone invasion and meningeal infiltration can be assessed.2, 3, 5, 18, 21
• For all tumours in the sublingual gland, MRI should be performed as the risk of malignancy is high. As a general rule, the proportion of malignant tumours increases as the salivary gland size decreases (parotid gland 20-30% malignant, submandibular 40-60%, minor salivary glands 50-80%, sublingual glands 70-90%)3, 16
• Sensitivity and specificity for MRI in differentiating malignant vs. benign salivary gland neoplasms are 83-86% and 85-92% respectively.12
• When it comes to perineural spread of tumours, MRI has shown to have a sensitivity of 100% and specificity of 85%.22

• Demonstrates abscess formation, calculi, major salivary duct dilatation and acute inflammation well.4, 17, 19
• Nearly always considered second line to MRI.
• Potentially falsely reassuring with predominent false negatives, when compared to MRI.
• In current practice, minor role for identifying major and minor salivary gland tumours and detecting direct extension to adjacent structures (particularly when bony erosion is a concern), neural and lymphatic invasion.14, 16, 23, 24
• Can be used to help to differentiate malignant from benign neoplasms (sensitivity 74-90%, specificity 79-90%), however, the combination of sensitivity and specificity in MRI is higher than for CT.12, 25
• Rapid and cheap compared to MRI but involves exposure to ionising radiation to the head and neck. Useful to assess neoplasms when MRI is contraindicated or where access to MRI is limited.2, 5

• Widely used for diagnosis of salivary gland tumours and can predict if the lesion is benign or malignant with an accuracy of 81-98%.26-29
• Although the combined sensitivity (80-82%) and specificity (95-97%) of FNAC in differentiating malignant from benign tumours is high, there is a relatively high non-diagnostic rate of about 10% due to sampling errors. It is currently recommended that neoplasms be characterised with cross-sectional imaging in conjunction with FNAC for pre-surgical decision making.26, 27, 30-33

Core needle biopsy (CNB)

Recent evidence from a meta-analysis reported that CNB provides much higher sensitivity than FNAC, similar high specificity, fewer non-diagnostic procedures (with less need for repeats) but a slightly increased (but rare) risk of haematoma 35.

• An invasive technique in which iodinated contrast is directly injected into the main ducts of the parotid or submandibular glands with radiographs obtained to allow detailed assessment of ductal strictures or presence of calculi.3, 4, 10
• Can be combined with therapeutic salivary interventional procedures which focus on gland preservation (e.g. stone retrieval, balloon ductoplasty of strictures) in some centres.3
• There are  risks of complications such as damage to the orifice, overfilling and rupture of the ductal system, exacerbation of infection, and adverse reactions to contrast material.2, 4, 10, 34
• Conventional sialography is generally superior to MR sialography in demonstrating very small calculi and detailing the smallest ductal branches
• MR sialography is superior to conventional sialography in demonstrating parenchymal changes
• Conventional sialography is contraindicated when there is acute salivary gland infection

CT can identify small calculi, especially in the submandibular gland where the vast majority are radio-opaque. CT can also assess gland atrophy, variant anatomy and help surgical planning

• Non-invasive method to characterise the ductal structure and identify calculi and stenosis of the parotid and submandibular glands.17
• Several studies have demonstrated that MR sialography is generally as accurate as conventional sialography in detecting obstructions, stenosis and stricture of the main ducts.17
• MR sialography is superior to conventional sialography in demonstrating parenchymal changes
• For the small percentage of radiolucent calculi, MR sialography has a role