Salivary Gland Abnormalities

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As the mouth is lined by stratified squamous epithelium, with salivary gland tissue in the
submucosa, abnormalities of the salivary gland may present in the mouth.
The most frequent abnormality is a mucocele (or mucous retention cyst).

These small cystic nodules on the lower lip (mucosal aspect) are the result of obstruction of the minor
labial salivary gland ducts, with cystic dilatation and retention of secretions. They are 
frequently traumatized, with escape of mucoid secretion into the surrounding tissues. A variant
of salivary mucocele occurs beneath the tongue, in association with the ducts of the sublingual
and submandibular salivary glands, forming a large, thin-walled, bluish cyst, commonly called
a ranula.

Salivary calculi from the submandibular or parotid glands may produce a swelling in the region
of the sites of emergence of their respective ducts into the mouth, i.e. sublingual and buccal
regions. The swelling may be due to retained secretion or to the calculus (sialolith) itself. 

Calculus formation in the ducts of the major salivary glands leads to chronic sialadenitis

Calculi or inspissated secretions that form in the major salivary ducts lead to obstruction in
the flow of salivary secretions. The back-pressure effects lead to dilatation of the ducts and
atrophy of the salivary acini, associated with increased interstitial fibrosis and lymphocytic
infiltrate. This is called chronic sialadenitis.
Salivary gland tumours

Salivary gland tumours are mainly benign, and most commonly affect the parotid gland

The parotid gland is the most common site for salivary gland tumours, under 25% occurring in the
other large salivary glands (submandibular and sublingual) and the minor salivary tissues of the
mouth. The most common tumour is the benign pleomorphic adenoma (formerly called 'mixed 
salivary tumour'), The peak incidence is in late middle-age and beyond, the tumour presenting as a slow-growing, smooth,
painless swelling. Despite its apparent encapsulation, there may be small nodules attached to
the main tumour which can be left behind at surgery if the main tumour is shelled out without 
a surrounding zone of normal salivary gland. This can lead to apparent recurrence of this benign
tumour. Adequate surgical excision in the parotid may be difficult because of the need to spare
the facial nerve, which runs between the deep and superficial parts of the parotid.

The second most common tumour is the monomorphic adenoma. This is behaviourally identical
to the pleomorphic adenoma, but has histological differences.

Warthin's tumour (adenolymphoma) is almost entirely confined to the parotid gland,
usually occurring in the lower border of the parotid, near the angle of the mandible. 

It is most common in middle-aged men and presents as a painless, spherical, smooth-surfaced
tumour, which may fluctuate in size. Larger tumours may be fluctuant because of central
necrosis or due to the presence of mucin. Histologically the tumour is unusual, with an 
epithelial component of tall eosinophilic columnar cells forming clefts and cystic spaces
within lymphoid tissue containing germinal centres. 

Malignant tumours of salivary tissue are rare and are particularly important in the intraoral minor salivary tissue

The most common malignant salivary tumour is the adenoid cystic carcinoma.
It can occur in the major salivary glands, such as parotid 
and submandibular glands, but is proportionally more common in the intraoral 
salivary tissue, e.g. the palate. A slow-growing but locally invasive tumour,
it frequently ulcerates in its intraoral location. Although it metastasizes 
late, the tumour has a poor prognosis because of its very extensive local invasion,
with a particular tendency to grow in the peri-neural spaces. The tumour often 
extends considerably further than is apparent to the naked eye, and primary surgical
excision is often unsuccessful in eradicating the tumour entirely, so further 
recurrence is very frequent. This, combined with poor radiosensitivity, makes management
of this tumour difficult. The second operation for recurrence frequently requires
radical and disfiguring orofacial surgery.

Two less common malignant tumours of salivary tissue are:

Mucoepidermoid carcinoma, which arises mainly in the parotid in elderly people, occasionally developing in the palate. These lesions are of variable malignancy:
some behave like pleomorphic adenoma, others are more aggressive from the outset.

Acinic cell carcinoma occurs mainly in the parotid in the middle-aged and elderly, and is more common in women than in men. It is sometimes called 'acinic cell tumour' because the majority behave in a benign fashion like pleomorphic adenoma, only rarely showing extensive local infiltration and lymph node metastasis.
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Revised: 02-11-2014.