Salivary gland disease
The salivary glands can be affected by any condition that blocks the duct, whether extra- or intraductal blockage or duct wall thickening. Sjögren’s syndrome is a chronic inflammatory disease of salivary and lacrimal glands. A number of tumours can also affect the glands themselves. The surgical management of salivary glands is described.
The submandibular gland is intermediate in size between the sublingual and parotid glands. It has a superficial part in the neck, a deep part in the floor of the mouth and it wraps around the posterior edge of the mylohyoid muscle. The superficial part is related to the facial artery, the facial vein, the cervical branch of the facial nerve, the mylohyoid nerve and the submandibular lymph nodes. The deep part is related to the lingual and hypoglossal nerves. Wharton’s duct emerges from the deep part of the gland and continues forward to empty at the sublingual papilla in the floor of the mouth. The sublingual gland empties into the floor of the mouth directly or through Wharton’s duct.
The parotid gland is the largest of the paired salivary glands. It occupies the region between the ramus of the mandible and the mastoid process, extending upwards to the external acoustic meatus and is essentially pyramidal in shape. The external carotid artery (deep), the retromandibular vein (intermediate) and the facial nerve (superficial) pass through the gland. The majority of the gland lies superficial to the facial nerve. Stenson’s duct runs through the cheek and drains into the oral cavity opposite the maxillary second permanent molar tooth.
Look for asymmetry and obvious extra- or intraoral swelling. In the case of the major salivary glands, establish if one or both glands are affected. Always palpate salivary glands bimanually. Is a swelling firm or soft? Larger calculi may be palpable as hard masses. In suspected inflammatory disease, see if clear saliva can be expressed from the duct orifice or, alternatively, whether turbid, mucopurulent secretion indicative of infection is present.
Malignant tumours in the salivary glands may present as fixed, firm, rapidly growing masses with pain and sometimes skin involvement. Facial nerve palsy is a sinister sign when a parotid mass is detected. Lymph node metastasis in the regional nodes may be present. It should be remembered that some salivary malignancies (e.g. adenoid cystic carcinoma) may be insidious. They may cause unilateral facial pain and remain undetected for a considerable period.
Hypersalivation may be a feature of certain neurological disorders. Sometimes it is confused with dribbling from the angle of the mouth caused by loss of neuromuscular control. Most often, hypersalivation is linked to a psychological disorder, when it is difficult to treat. It is sometimes seen in sialosis, which presents as painless bilateral parotid gland swelling.
Dry mouth is a frequent complaint and there may be a sensation of dry mouth with no objective reduction in flow. Sialometry is a simple first-line investigation that can help to identify reduced salivary flow (xerostomia). The most common cause of true xerostomia is the unwanted effects of drugs with sympathomimetic or antimuscarinic effect (e.g. tricyclic antidepressants and antihistamines). Treatment of xerostomia is discussed later with Sjögren’s syndrome.
Normal whole unstimulated salivary flow rates can be assessed by asking the patient to gently dribble any saliva produced over a 5-minute period into a container. The normal flow rate is 0.3–0.4 ml/min; a flow rate of ≤0.1 ml/minute indicates a clinically significant xerostomia.
Parotid glands: Intraoral plain radiographs of the cheek (dental film placed in the buccal sulcus over the parotid orifice) and an anteroposterior radiograph of the face, with the patient requested to inflate the cheek, are required. Additional, lateral views are often taken, but any calculus may be superimposed upon bone or teeth and obscured.
Submandibular gland: The plain radiographic examination consists of a true occlusal radiograph of the floor of the mouth (Fig. 13.1) and a ‘special’ (oblique occlusal) radiograph with the beam angled anterosuperiorly while centred on the gland itself. Lateral views may be useful, although again a calculus may be superimposed upon bone and be difficult to identify.
Sialography: Both these questions are best answered with sialography. Sialography is the introduction of a radio-opaque contrast medium into the orifice of one of the major salivary glands via a cannula. The media used are all iodine-containing solutions (usually low osmolarity aqueous solutions of iodine salts). The contrast is introduced slowly until discomfort is felt by the patient. Alternatively, the procedure is performed under fluoroscopic screening, allowing ‘real-time’ imaging. Usually two images are made at different angles (e.g. lateral and anteroposterior views). After this, the cannula is removed and a ‘drainage’ image obtained, usually after stimulation using a sialogogue (e.g. citric acid solution, lemon juice). Digital subtraction may be used to remove bone and tooth images, leaving the contrast image in isolation (Fig. 13.2).
Ultrasound: This is the ‘first-line’ investigation for a mass (Fig. 13.3). A high-frequency transducer is used to obtain images in several planes of the gland. Bony superimposition may prevent complete imaging of the deep lobe of the parotid and that part of the submandibular gland immediately adjacent to the mandible. Where a lesion is completely visualised on ultrasound and where there is no suggestion of malignancy, an ultrasound examination is often sufficient for surgical planning.
Radioisotope imaging: This is a question usually asked in relation to Sjögren’s syndrome. The only radiological technique that can assess function is radioisotope imaging (nuclear medicine). This uses a radiopharmaceutical injected intravenously. The radiopharmaceutical is a molecule containing the isotope 99 m technetium as the pertechnate (a gamma ray emitter). Once in the bloodstream, this is handled by the body in the same way as iodine and is taken up by the salivary glands and then secreted in saliva. The gamma rays are detected by a gamma camera to produce an image representing the functional activity of the glands (Fig. 13.4). It is possible to quantify activity in addition to subjective assessment of images. This technique is also employed in rare cases where aplasia of one or more major glands is suspected.
Fig. 13.4 Radioisotope scan of the salivary glands.
Each image is taken with the patient facing the gamma camera, giving a ‘face-on’ image. The highly active bilobed area of activity at the bottom of each image is the thyroid gland. In this particular patient, the problem illustrated by the quantitative study was underactivity of the right parotid. Lt, left; Rt, right; subman., submandibular.
Biopsy of labial minor salivary lobules is sometimes used to assess overall salivary function. Incisional biopsies of intraoral salivary masses are undertaken through mucosa that will be later removed as a planned surgical procedure.
On no account should a discrete salivary gland mass in a major gland be subjected to incisional biopsy, this may lead to recurrence and is usually unnecessary. For example, there is a 9 in 10 chance that a single parotid mass is a pleomorphic adenoma and so the only acceptable biopsy is a superficial parotidectomy. This will ensure removal of the tumour together with a surrounding margin of normal tissue. Fine-needle aspiration or needle core biopsy is acceptable and is without the risk of implantation of malignant cells in the needle tract. Frozen section may be useful at surgery for tumours in the parotid gland that are thought likely to be malignant, to establish whether the facial nerve may be preserved.
Obstructive salivary disease can be acute or chronic. The clinical features are characteristically pain and swelling of the affected gland just before meals. Astringent stimuli produce severe symptoms. Sometimes the swelling slowly subsides as saliva leaks past the obstruction, and a bad taste is suggestive of associated sialadenitis (Fig. 13.5).
Extraductal obstruction is caused by disease outside the duct wall. The most important cause is neoplasia, particularly squamous carcinoma in the floor of the mouth or salivary neoplasms. Trauma may also lead to displacement of soft or hard tissue, resulting in duct obstruction.
Duct wall obstruction may be related to fibrosis, leading to stricture. The orifices can become stenosed through trauma from dentures or teeth. Rarely, intraduct papillomas arise from the duct wall and obstruct the lumen.
Salivary calculus is the most common type of obstructive disorder (Fig. 13.6). The submandibular gland is most frequently involved (around 80% of cases), followed by parotid and, rarely, minor glands. The calculi (sialoliths) tend to be hard, yellowish and often have a lamellated, concentric-ring structure. They are composed of calcium phosphates, thought to be nucleated on microcalculi, which are commonly found in the major and minor glands. Salivary calculi may form in ducts within the gland substance.
Viral sialadenitis (mumps) is an acute contagious infection caused by a paramyxovirus. Spread is caused by direct contact with infected saliva and by droplets. There is a 2–3 week incubation period, and fever and malaise are followed by sudden, painful swelling of one or both parotid glands. In adults, viraemia results in involvement of internal organs such as the central nervous system and gonads. Orchitis (gonadal swelling) occurs in around 20% of affected adult males. Diagnosis is made on clinical grounds and bedrest is advised. As the disease occurs in minor epidemics, infected persons should avoid contact with those at risk. Virus is present in the saliva when symptoms commence and remains for approximately 6 weeks. One episode usually confers lifelong immunity.
Acute bacterial sialadenitis principally involves the parotid glands and is caused by bacteria entering the ductal system against the salivary flow. Reduced flow is a common predisposing factor and is a feature of many conditions, including chronic sialadenitis, Sjögren’s syndrome and unwanted effects of drugs. Streptococcus pyogenes, Staphylococcus aureus, Haemophilus species, black-pigmented bacteroides and other oral bacteria may be detected in mucopurulent discharge from the duct opening, which is an important clinical sign. It is accompanied by swelling, pain, fever and erythema of the overlying skin. Treatment is by antibiotic therapy and gentle massage to encourage flow. Warm, salty mouthrinses may be helpful, and patients should be advised against placing a hot-water bottle over the gland as this may lead to a pointing abscess.
Chronic bacterial sialadenitis is related to low-grade bacterial invasion through the duct system and often follows chronic obstructive disease. The submandibular salivary gland is most commonly affected. Typically, there is recurrent, painful swelling associated with eating or drinking. The duct orifice appears inflamed and a mucopurulent discharge may be seen on examination. Patients may complain of a salty or foul taste in the mouth. The gland may become firm and fibrotic at the end stage. Pathologically there may be duct ectasia, mucous metaplasia of duct epithelium, periductal fibrosis and elastosis, acinar atrophy and a chronic inflammatory infiltration. Interlobular fibrosis results in fusion of the lobules. Surgical removal is indicated in intractable disease. On sialograms, there are combinations of sialectasis (ductal dilatation), strictures, filling defects with calculi or stagnant secretions and atrophy of minor salivary ducts (Fig. 13.7). In advanced disease, large abscess cavities may form.
Fig. 13.7 Chronic sialadenitis of the parotid gland.
The main duct has a reasonably normal diameter and course, but beyond the point of junction with an accessory gland (seen passing vertically upwards from the main duct), the gland is abnormal. The ducts are dilated and there is some atrophy of the peripheral ducts (compare with Fig. 13.1). A filling defect is visible centrally, indicating the presence of a substantial mucus plug or calculus.
Relapsing (recurrent) parotitis is an uncommon disorder affecting children and sometimes adults. Typically, sialography shows normal main ducts but punctate sialectasis peripherally. Some cases are bilateral, suggesting a congenital duct abnormality or tendency to reduced flow.
Radiation sialadenitis occurs mostly after radiotherapy, particularly when given for head and neck cancers. There is acinar damage and progressive fibrous replacement. Depending on dose, some recovery may be seen. The glands are shielded where possible to avoid this unwanted effect (Fig. 13.8) and techniques such as intensity modulated radiotherapy (IMRT) can be used to direct radiation and spare salivary glands. See Sjögren’s syndrome for treatment of xerostomia.
Also known as Kuttner tumour, this disorder presents as a firm tumour-like mass affecting the submandibular gland. There are increased numbers of IgG4-secreting plasma cells in the gland parenchyma. Dense fibrosis is also present. Kuttner tumour may be part of a generalised immune disorder that can be treated by immunosuppressive therapy.
Bilateral parotid swelling may be caused by chronic granulomatous inflammation, as part of the multisystem disorder sarcoidosis. Confluent sheets of non-caseating granulomas (aggregates of macrophages) are found in the gland parenchyma. The lacrimal glands may be involved resulting in dry eyes and mouth. Diagnosis may be made by needle core biopsy and estimating serum ACE. Referral to a physician is necessary as pulmonary lesions may be present and systemic immunosuppressive therapy is then indicated.
Also known as sialadenosis, this condition is characterised by recurrent bilateral swelling of the salivary glands, most often the parotids. Sialosis is a non-inflammatory and non-neoplastic disorder, probably due to abnormality of neurosecretory control. A number of underlying disorders may be present including liver cirrhosis, alcoholism, eating disorders, malnutrition, drug therapy and hormonal abnormalities. Microscopically, the acinar cells show hypertrophy and the cytoplasm is packed with prominent zymogen granules.
Sjögren’s syndrome is an autoimmune chronic inflammatory disease involving the salivary and lacrimal glands. It is characterised by polyclonal B-cell proliferation, probably as a result of loss of T-cell regulation. There is lymphocytic infiltration and destruction of glandular parenchyma (Fig. 13.9). Sjögren’s syndrome can have widespread manifestations and is classified into:
There is some overlap between the two forms, though in general oral and ocular dryness is more severe in primary Sjögren’s syndrome. Widespread symptoms may be experienced in both types, including nasal and vaginal dryness, dysphagia and dry skin. Fatigue syndrome is commonly present. Autoimmune connective tissue diseases that may be associated with secondary Sjögren’s syndrome are given in Box 13.1. Rheumatoid disease (arthritis) is the most commonly associated disorder.
Clinically, middle-aged females are most commonly affected, though Sjögren’s syndrome may occur in childhood. Sjögren-like features can be seen in other T-cell dysfunctions including HIV infection, therapeutic immunosuppression and graft-versus-host disease. Patients often complain of difficulty in eating dry foods and the tongue adhering to the palate. Symptoms are usually worst during the night and sleep may be disturbed. Difficulty in swallowing, speaking and wearing dentures may be experienced. The oral mucosa appears glazed and the tongue may become lobulated and beefy-red. Oral candidiasis is common and there may be patches of erythema or even ulceration. The major salivary glands may be enlarged. Sudden expansion may be a result of obstruction, acute infection or transformation to malignant lymphoma.
Sjögren’s syndrome is a clinical diagnosis and a number of investigations may aid in diagnosis. The ethics and costs of laboratory and clinical tests should be considered, particularly if results do not affect management.
Estimation of salivary flow (sialometry test) and lacrimal flow (Schirmer test; Fig. 13.10) are inexpensive simple tests. Often, detection of autoantibodies against Ro (SS-A) and La (SS-B) extractable nuclear antigens (ENA) can be used as reasonably sensitive and specific tests. Other autoantibodies may be detected by arranging a panel of tests, as determined by evidence-based laboratory medicine. Tests that may be utilised for the diagnosis of Sjögren’s syndrome are shown in Box 13.2. Sialographically, the classic features are varying degrees of punctate and globular sialectasis with fairly normal main ducts. However, secondary obstruction and infection means that changes often become similar to chronic sialadenitis (Fig. 13.11). There is accumulating evidence to support the role of ultrasound of the salivary glands in the diagnosis of Sjögren’s syndrome.