Sialolithiasis

Calculus formation within a salivary gland or its duct, accounting for around 60 to 70 percent of all salivary gland disease and for the majority of cases of obstructive sialadenitis.

Distribution and why the submandibular gland dominates

• Submandibular gland: 80 to 90 percent of stones. Four anatomical and biochemical factors explain this:
• Wharton duct runs upward and forward against gravity from the gland in the submandibular triangle to the papilla at the anterior floor of mouth, so drainage is uphill.
• The duct is long, around 5 cm, with a sharp bend around the posterior border of mylohyoid at the genu, which is a point of stasis.
• Submandibular saliva is mucinous, more viscous, and alkaline, with a higher concentration of calcium and phosphate and higher hydroxyapatite saturation than parotid saliva.
• The duct orifice is narrow relative to the duct calibre.
• Parotid gland: 10 to 20 percent. Stensen duct is around 5 cm, runs horizontally across masseter, turns medially through buccinator, and opens opposite the second upper molar. Parotid saliva is serous and less lithogenic.
• Sublingual and minor glands: under 1 percent.

Composition and formation

Stones consist of a core of organic material, that is desquamated epithelium, mucus, bacteria and glycoproteins, surrounded by concentric laminated layers of calcium phosphate as hydroxyapatite, with smaller amounts of calcium carbonate, magnesium and ammonium. Around 80 to 90 percent of submandibular stones are radiopaque; only around 40 to 60 percent of parotid stones are, since they are less calcified. This difference matters when interpreting a negative plain film.

Formation is promoted by salivary stasis, dehydration, altered salivary composition, chronic inflammation with ductal metaplasia, and anticholinergic and diuretic medication. Systemic calcium metabolism is generally normal, and sialolithiasis is not a manifestation of hypercalcaemia or of nephrolithiasis, which is a common misconception. Routine calcium and parathyroid testing is not indicated unless there are other reasons.

Consequences of obstruction

Retrograde ascent of oral flora produces acute suppurative sialadenitis. Chronic partial obstruction produces recurrent inflammation, acinar atrophy, periductal fibrosis, ductal ectasia and eventually a non functioning fibrotic gland.

• Postprandial swelling and pain, that is mealtime syndrome, which is the pathognomonic feature. Salivary flow is stimulated by the sight, smell and taste of food, saliva accumulates behind the obstruction, and the gland swells rapidly and painfully within minutes of eating, then subsides over 1 to 2 hours as saliva slowly passes. Ask specifically about the timing relative to meals, since this history alone establishes the diagnosis in most patients.
• Colicky pain radiating to the ear, angle of the jaw or floor of the mouth.
• A palpable stone at the duct orifice or along the duct.
• Purulent or gritty discharge from the duct orifice.
• Foul taste.
• Symptoms may be intermittent over months to years, with periods of complete resolution when the stone shifts.
• Chronic cases: a persistently enlarged, firm, sometimes non tender gland with reduced or absent salivary flow.

Acute suppurative sialadenitis complicating obstruction

• Rapidly increasing painful swelling, erythema of the overlying skin, fever, malaise and trismus.
• Pus expressible from the duct orifice on bimanual massage.
• Fluctuance indicating abscess.
• Systemic sepsis in the immunocompromised, diabetic and elderly.

Examination

• Bimanual palpation with one finger in the floor of mouth and the other hand externally under the mandible, which is the essential examination technique and which detects stones in the distal and mid Wharton duct that are impalpable externally. Palpate along the whole course of the duct from the papilla backward.
• Massage the gland toward the orifice and observe the character of the expressed saliva: clear, turbid, purulent or absent.
• Inspect the duct orifice for erythema, dilation, a protruding stone or purulence.
• Assess for facial nerve function in parotid disease, since facial weakness with a parotid mass indicates malignancy rather than inflammation.
• Neck examination for lymphadenopathy.

Red flags indicating a diagnosis other than simple sialolithiasis

• Facial nerve weakness with a parotid swelling, which indicates malignancy until proven otherwise.
• A hard fixed mass, skin involvement or ulceration.
• Cervical lymphadenopathy.
• Persistent swelling unrelated to meals.
• Bilateral gland enlargement, which suggests Sjögren syndrome, sarcoidosis, HIV, lymphoma, IgG4 related disease, bulimia or alcoholism rather than stones.
• Rapid progressive enlargement.
• Systemic sepsis.

• History of mealtime syndrome plus bimanual palpation, which establishes the diagnosis in a large proportion.
• Ultrasound, which is the first line imaging investigation. It is non invasive, radiation free, cheap and repeatable, detects stones above 2 mm with a sensitivity of around 90 percent, demonstrates ductal dilation proximal to the obstruction, assesses gland parenchyma and detects abscess and masses. It should be the default first imaging test.
• Plain radiography: a lower true occlusal film for anterior and mid Wharton duct stones, and an anteroposterior or oblique film for parotid stones. Cheap and useful where ultrasound is unavailable, but it misses radiolucent stones and around 20 percent of submandibular and 40 to 60 percent of parotid stones.
• Non contrast computed tomography, which is highly sensitive for calcified stones and which defines size, number and position accurately. It is the best modality for planning surgery for a large or intraparenchymal stone.
• Cone beam computed tomography, which gives excellent detail with a lower radiation dose.
• Magnetic resonance sialography, using heavily T2 weighted sequences to image the fluid filled duct without contrast or cannulation, which demonstrates ductal anatomy and strictures. Stones appear as filling defects.
• Conventional sialography with retrograde contrast injection, which gives excellent ductal detail but which is contraindicated during acute infection since it can force organisms into the parenchyma. It has been largely replaced by ultrasound and sialendoscopy.
• Diagnostic sialendoscopy, which directly visualises the duct system, identifies stones, strictures, mucous plugs and inflammatory changes, and which is simultaneously therapeutic. It has become the reference standard where available.
• Fine needle aspiration cytology of any mass or persistently enlarged gland where neoplasm is a possibility.
• Full blood count, C reactive protein, glucose and HbA1c where infection is present.
• Culture of expressed pus.
• Consider Sjögren syndrome with anti Ro and anti La antibodies, and consider sarcoidosis, HIV and IgG4 related disease, where the picture is bilateral or atypical.

Differential diagnosis

• Ductal stricture, which produces an identical mealtime syndrome without a stone and which is diagnosed on sialendoscopy or magnetic resonance sialography.
• Mucous plug, which produces intermittent obstruction and which is relieved by sialendoscopic irrigation.
• Salivary gland neoplasm, benign or malignant.
• Sjögren syndrome, sarcoidosis, IgG4 related disease and HIV associated lymphoepithelial lesions, all of which cause bilateral gland enlargement.
• Viral parotitis, that is mumps, which is bilateral in most cases and occurs in the unvaccinated.
• Lymphadenopathy, particularly intraparotid nodes.
• Masseteric hypertrophy in the parotid region.
• Dental and odontogenic infection.
• Sialadenosis, that is a bilateral painless non inflammatory enlargement associated with diabetes, alcoholism, bulimia, malnutrition and endocrine disease.

The principle has shifted decisively from gland removal to gland preservation. Sialendoscopy and minimally invasive techniques allow around 80 to 90 percent of glands to be saved, and sialadenectomy should now be a last resort rather than a first line procedure.

Conservative management

Appropriate for small stones under 2 to 3 mm and for the initial episode.

• Hydration, which increases salivary flow.
• Sialogogues: sour sweets, lemon juice, citrus and chewing gum, taken regularly to stimulate flow and encourage stone passage.
• Gland massage from posterior to anterior along the duct, taught to the patient and performed several times daily.
• Warm compresses.
• Analgesia with paracetamol 1 g every 6 hours and a nonsteroidal anti inflammatory drug.
• Avoid anticholinergics, antihistamines and diuretics where possible.
• Small stones pass spontaneously in a substantial proportion with these measures.

Acute suppurative sialadenitis

• Antibiotics covering oral flora including anaerobes and Staphylococcus aureus: co amoxiclav 625 mg orally three times daily for 7 to 10 days, or 1.2 g intravenously every 8 hours in severe disease. Clindamycin 300 to 450 mg four times daily in penicillin allergy, which gives good salivary gland penetration and anaerobic cover. Flucloxacillin plus metronidazole is an alternative.
• Add vancomycin where methicillin resistant Staphylococcus aureus is suspected.
• Hydration, intravenous if necessary.
• Sialogogues and massage once the acute inflammation is settling, though massage during peak acute infection is painful and may be deferred.
• Analgesia.
• Ultrasound to identify an abscess.
• Incision and drainage of any abscess, which for the parotid is performed with an incision parallel to the facial nerve branches and blunt dissection to avoid nerve injury.
• Optimise glycaemic control.
• Do not perform sialography or sialendoscopy during acute suppuration.
• Definitive treatment of the stone is deferred for 4 to 6 weeks until the acute episode has settled.

Interventional and minimally invasive techniques

• Transoral duct slitting for a stone palpable in the distal or mid Wharton duct. Perform under local anaesthesia, place a suture proximal to the stone to prevent it slipping backward, incise the duct longitudinally over the stone, deliver the stone, and marsupialise the duct to the floor of mouth mucosa with fine absorbable sutures rather than closing it, which prevents stricture. Take care to identify and preserve the lingual nerve, which crosses beneath the duct in the posterior floor of mouth from lateral to medial, and which is the structure at risk in posterior stone removal.
• Sialendoscopy: a semi rigid endoscope of 0.8 to 1.6 mm is passed through the dilated papilla into the duct under saline irrigation. Stones up to around 4 mm in the parotid and 5 mm in the submandibular duct can be retrieved intact with wire baskets or grasping forceps. Larger stones require fragmentation first.
• Intracorporeal lithotripsy using a pneumatic, laser or electrohydraulic probe delivered through the sialendoscope, fragmenting the stone in situ for basket retrieval.
• Extracorporeal shock wave lithotripsy, which fragments stones without instrumentation and which is suitable for intraparenchymal stones and for parotid stones. Success rates are moderate, multiple sessions are required, and complete clearance is achieved in around 40 to 60 percent.
• Combined or hybrid approach: sialendoscopy combined with a transoral or transcutaneous incision, in which the endoscope light is used to localise the stone through the tissues and a small incision is made directly over it. This is the technique that has most extended gland preservation, allowing removal of large and hilar stones that were previously an indication for gland excision.
• Balloon dilation of associated strictures at the same procedure.
• Steroid irrigation of the duct at the end of the procedure to reduce inflammation and stricture formation.
• Stent placement in the duct for a period after intervention where stricture is a risk.

Selection by stone characteristics

• Distal, mobile, palpable stones: transoral duct slitting or basket retrieval.
• Stones under 4 to 5 mm anywhere in the duct: sialendoscopic basket retrieval.
• Stones 5 to 10 mm: fragmentation with intracorporeal lithotripsy, or a combined approach.
• Stones over 10 mm, hilar stones, and intraparenchymal stones: combined approach or extracorporeal lithotripsy.
• Multiple stones, an atrophic non functioning gland, extensive ductal disease, or failure of gland preserving techniques: sialadenectomy.

Sialadenectomy

• Submandibular gland excision through a transcervical incision two fingerbreadths below the mandible to avoid the marginal mandibular branch of the facial nerve. Structures at risk are the marginal mandibular nerve, the lingual nerve which must be identified and released from the submandibular ganglion, and the hypoglossal nerve deep to the gland.
• Parotidectomy, usually superficial, with formal facial nerve identification and dissection.
• Complications: nerve injury, haematoma, infection, sialocele, salivary fistula, and for the parotid, Frey syndrome with gustatory sweating.
• Reserve for the failed or non functioning gland, and explain to patients that gland preservation is the modern default so that they understand why a less invasive approach is being attempted first.

Follow up and prevention

• Lifelong hydration, regular sialogogue use, and gland massage.
• Avoid anticholinergic medication where possible.
• Good oral hygiene and dental care.
• Smoking cessation.
• Recurrence occurs in around 10 to 20 percent after gland preserving treatment, and patients should be told this and instructed to present early with recurrent mealtime symptoms.
• Ultrasound surveillance where multiple stones were present or where clearance was incomplete.