Salivary Gland Imaging
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Direct answer
Salivary gland imaging begins with the clinical question — stone, inflammatory destruction, mass or functional failure — because each route to a different modality. Ultrasound is today's first-line for stones and masses alike, painless and radiation-free; sialography, the historic gold standard of ductal anatomy, retains a selective role with its contraindication in acute sialadenitis; MR sialography images ducts without cannulation; scintigraphy with 99mTc-pertechnetate measures function in Sjogren's and the dry-mouth workups; and sialendoscopy has matured from diagnostic curiosity into the gland-preserving treatment of ductal stones and strictures. The classical patterns — submandibular predominance of stones, the "pruned tree" of chronic sialadenitis and the punctate sialectasia of Sjogren's — remain the vocabulary of every examination on this topic.
What you must remember
- Stones: roughly 80-90 per cent arise in the submandibular gland (alkaline, mucoid saliva, long uphill duct); a share are radiopaque — older texts quote up to about 80 per cent — so plain films (an occlusal view for the floor of mouth) still earn their place before cross-sectional imaging.
- Ultrasound, the modern first-line: detects stones from about 2 mm, separates intraglandular from extraglandular masses, characterises cysts and abscess, and images lymph nodes — operator-dependent, and limited for deep parotid lobe and fine ductal detail.
- Sialography: cannulation of Wharton's or Stensen's duct with aqueous or oil-based contrast demonstrates ductal anatomy, filling defects (stones, strictures) and emptying function; absolutely contraindicated in acute sialadenitis (risk of spreading infection) and in iodine sensitivity.
- Sialographic patterns to recite: normal — a fine branching "tree"; chronic sialadenitis — dilated, pruned, beaded "pruned tree"; Sjogren's — punctate, then globular, then cavitary sialectasia, the "apple-blossom" clusters.
- MR sialography images ducts without cannulation or radiation — stones appear as signal voids — suited to Sjogren's assessment and patients unsuited to cannulation.
- Scintigraphy with 99mTc-pertechnetate grades salivary function by uptake and stimulated secretion: the functional test in Sjogren's staging, where structural imaging alone underestimates gland failure.
- CT and MRI answer the mass question — deep lobe extent, nodal status, skull base relations; PET complements in proven malignancy.
- Sialendoscopy passes miniature semi-rigid endoscopes (commonly 0.9-1.3 mm) into the ducts to visualise, retrieve stones with baskets, dilate strictures and lavage — the gland-preserving alternative to blind stone surgery.
Working up two different swellings
A 38-year-old reports meal-time swelling under the left jaw for three months, aching and subsolving within an hour of eating. The story is obstructive: bimanual palpation of the floor of mouth, then ultrasound, which demonstrates an echogenic focus with acoustic shadow at the hilum of the submandibular duct and a dilated proximal duct — a stone. An occlusal radiograph confirms a radiopaque calculus; the gland parenchyma is preserved, so the plan is sialendoscopic retrieval under local anaesthesia with basket extraction and ductal lavage, reserving gland excision for destroyed glands or irretrievable hilar stones. The second patient, a 52-year-old woman with dry eyes and dry mouth for two years, follows a different algorithm entirely: ultrasound of the major glands for echotexture, MR sialography revealing punctate and globular sialectasia, serology for anti-Ro and anti-La antibodies, unstimulated salivary flow measurement, and scintigraphy staging secretory impairment — the structural-plus-functional workup that diagnoses Sjogren's rather than merely labelling dryness. Same organ system, opposite ends of the imaging ladder, and the clinical question — obstructive versus functional — chose the route.
Where students slip
The contraindication question is the trap most often sprung: sialography performed during acute sialadenitis converts a blocked gland into an infected one, and the answer "acute sialadenitis" must come without hesitation. The second slip is pattern confusion — assigning punctate sialectasia to chronic sialadenitis or the pruned tree to Sjogren's inverts the two classic pictures the examination exists to test. The third is first-line drift: answering "sialography" to the question of initial imaging, when contemporary practice — and therefore the contemporary answer — begins with ultrasound. Finally, know the stone arithmetic: submandibular predominance and the radiopacity caveat, because a normal plain film has never excluded a radiolucent parotid calculus.
Frequently asked questions
Which gland accounts for most stones, and why?
The submandibular — 80-90 per cent — for mucoid alkaline saliva, a long uphill duct and a wide lumen favouring stasis.
What is the first-line imaging modality today?
Ultrasound — radiation-free — for stones, inflammatory change and masses, with cross-sectional imaging for deep or extensive disease.
When is sialography contraindicated?
In acute sialadenitis, iodinated contrast sensitivity, and patients unsuited to cannulation.
Describe the Sjogren's sialographic pattern.
Progressive punctate, then globular, then cavitary sialectasia — the apple-blossom appearance from periductal lymphocytic infiltration.
What does scintigraphy contribute?
99mTc-pertechnetate grading of uptake and stimulated secretion — the functional dimension in Sjogren's staging.
What is sialendoscopy used for?
Miniature endoscopes visualise and treat ductal stones and strictures — the gland-preserving management of obstruction.