Sialography

Sialography is a radiographic or fluoroscopic study of the salivary ducts and glands after a small volume of contrast is injected retrogradely through the duct opening. The parotid (Stensen) duct opens opposite the second upper molar, and the submandibular (Wharton) duct opens at the sublingual papilla at the side of the frenulum of the tongue.

A fine cannula is placed in the duct orifice, usually after dilating the opening with lacrimal probes, and 0.5 to 2 mL of water soluble contrast (an oil based agent was used in the past) is injected gently until the patient feels fullness or pressure.

Images are taken in the anteroposterior and lateral (or oblique) projections during filling, at full filling, and after emptying (a post-evacuation film taken after sucking a lemon wedge or sialogogue, which tests the clearance of contrast from the ducts and acini). Digital subtraction and fluoroscopy shorten the study, and cone beam CT sialography adds three dimensional information.

The effective dose is about 0.05 to 0.2 mSv.

Salivary gland disease is common: stones (sialolithiasis) affect about 1 in 100 people and cause 50% of major salivary gland diseases, and 80 to 90% of stones are in the submandibular system. Ultrasound is the first line test for the major salivary glands, and MR sialography, CT and ultrasound with scintigraphy have replaced much of the conventional sialography.

Conventional sialography is still the most detailed test of the duct system and is used for chronic obstructive disease, strictures, and before or during interventional sialendoscopy.

Indications. Recurrent painful swelling of a parotid or submandibular gland, particularly around meals (obstruction). Suspected salivary duct stones, strictures or fistulae, when ultrasound is inconclusive. Chronic recurrent sialadenitis (including juvenile recurrent parotitis). Sjogren syndrome, as one test of the changes in the gland.

Suspected salivary duct injury after trauma or surgery. Salivary fistula or sinus. Assessment of tumours (rarely, because MR and ultrasound show masses better). Dry mouth with suspected ductal disease. Pre-operative planning. Not during acute infection of the gland, and not for a salivary mass for which cross-sectional imaging and biopsy are used.

Contraindications and precautions. Acute sialadenitis or abscess (risk of spreading infection and severe pain; study after the infection settles). Allergy to iodinated contrast (a small amount reaches the circulation, but the contrast may be absorbed through the gland). Thyroid disease (iodine load is small). Pregnancy: avoid unless essential.

A stone near the duct opening may be pushed back by the cannula, so a plain occlusal film or ultrasound is done first to locate calculi. Oil based contrast is avoided because of extravasation and granuloma. Local anaesthetic gel may reduce discomfort. A patient who cannot co-operate or keep still may not tolerate the study.

Preparation and technique. No fasting is needed. A plain film (anteroposterior or occlusal) is taken first. The duct opening is found with a good light, dilated gently with a lacrimal probe, and a cannula or catheter is placed and secured.

The contrast is injected by hand slowly under fluoroscopy and the injection stops at the first sign of pain or tightness, or when the gland is filled. Films are taken immediately, and a film after emptying is taken 5 minutes after a sialogogue. The patient is warned of a swollen gland and pain for 1 to 2 days, and that a gland that fails to empty should be massaged.

Normal appearances. The parotid duct is 5 to 7 cm long with a diameter of 1 to 2 mm, runs forward from the gland over the masseter and turns medially through the buccinator, and the main duct has smooth walls. Intraglandular ducts show a "tree in winter" pattern, branching in a regular and tapering way. The acinar phase shows a fine, uniform blush that fills the glandular area.

The submandibular duct is 5 cm long and about 1 to 2 mm in diameter, passes forward and upward from the gland, and ends in an opening at the sublingual papilla. Both ducts empty within 5 minutes after sialogogue stimulation, and no more than a trace of contrast remains.

Interpretation.

• Sialolithiasis: a stone shows as a filling defect (a sharp edged round or oval defect) in the duct, with dilatation behind it; radio opaque stones (80% in the submandibular gland, 60% in the parotid) are seen on plain films. A stone with a stricture or infection leads to a dilated duct with a swollen gland on the delayed film.
• Ductal stricture: a focal narrowing with upstream dilatation ("sausage link" or "beaded" duct from multiple strictures and dilatations), caused by stones, infection or radiotherapy.
• Chronic sialadenitis: dilated, irregular ducts with a "sialectasis" pattern, with contrast pooling in punctate collections (punctate, globular, cavitary, or destructive sialectasis, in order of severity) and delayed or absent emptying; the "snowstorm" or "apple tree in bloom" appearance of punctate sialectasis is typical of Sjogren syndrome, and in juvenile recurrent parotitis.
• Sjogren syndrome: punctate sialectasis (1 mm), globular (1 to 2 mm), and cavitary (over 2 mm) collections, with a pruned or sparse duct tree; ultrasound and scintigraphy are used more often now.
• Sialodochitis: irregular narrowing and dilatation of the main ducts.
• Tumour: displacement and splaying of ducts around a mass ("ball in hand" sign for a benign mass such as pleomorphic adenoma), and destruction, irregular filling or extravasation in malignant tumours; cross-sectional imaging and biopsy are needed.
• Duct injury and fistula: extravasation of contrast outside the duct, or a communication with the skin.
• Sialocele and ductal cyst: contrast pooling in a cavity connected to the duct.
• Congenital anomalies: accessory parotid gland and duct, duct duplication, and aplasia.
• Granulomatous disease (sarcoidosis, tuberculosis): distorted ducts with filling defects.

Critical values and findings needing immediate action.

• Acute swelling with fever, spreading cellulitis, trismus or floor-of-mouth swelling after the study: antibiotics, hydration, sialogogues and imaging for abscess; airway assessment if swelling extends in the neck.
• Extravasation of contrast into the tissues with severe pain or swelling: stop injection, analgesia, antibiotics if infection occurs.
• Anaphylaxis: stop, adrenaline, oxygen and resuscitation.
• Findings of a malignant tumour (irregular destruction, facial nerve weakness, fixed mass): urgent MR, biopsy and head and neck oncology referral.
• Impacted large stone with abscess: urgent drainage and surgical or sialendoscopic removal.

Limitations and artefacts.

• Cannulation can be difficult, especially in small or inflamed duct openings, and the duct may be injured or perforated; extravasation from over injection mimics a leak or cyst.
• Over distension produces false dilatation and causes pain, and air bubbles mimic stones (they move with positioning and change with injection).
• Unlike MR sialography, conventional sialography shows only the ductal tree and acinar phase and not the gland parenchyma or surrounding tissues.
• It is invasive, with a small risk of infection, pain, ductal injury or stricture, and contrast reaction.
• Dilatation of ducts with mucus plugs and debris mimic stones, and a negative sialogram does not exclude small stones that were pushed back.
• Sialography is contraindicated in acute infection, which is the time when patients present, so it is usually delayed.
• Interpretation of duct patterns in Sjogren syndrome has a wide overlap with chronic sialadenitis of any cause.
• Radiation dose is low, but may be avoided with MR or ultrasound; sialendoscopy has become the diagnostic and treatment test for obstructive disease.

Special groups.

• Children: recurrent parotitis of childhood is investigated with ultrasound; sialography is used rarely and with sedation if required.
• Patients with Sjogren syndrome: ultrasound, scintigraphy and labial gland biopsy are alternatives.
• Patients with HIV: benign lymphoepithelial cysts of the parotid and diffuse infiltrative lymphocytosis syndrome.
• Patients after radioactive iodine or radiotherapy: ductal strictures and dry mouth.
• Pregnancy: avoid.
• Regions: stone disease, tuberculous sialadenitis, HIV-associated parotid disease and mumps are important, and sialography may be the only way to show the duct system when ultrasound and MR are not available.

Follow up tests. Ultrasound of the salivary glands, MR sialography, CT or cone beam CT, sialendoscopy for diagnosis and stone removal, salivary scintigraphy for function, fine needle aspiration cytology or core biopsy for masses, labial salivary gland biopsy, antinuclear antibodies, anti-Ro and anti-La antibodies, rheumatoid factor and immunoglobulins for Sjogren syndrome,

HIV test, serum angiotensin converting enzyme for sarcoidosis, tuberculosis tests, and referral to oral and maxillofacial, ear nose and throat, or rheumatology services.