PATHOLOGY OF THE SALIVARY GLANDS

Mucocele

• Most common of the obstructive disorders; results from trauma to minor salivary glands with extravasation and pooling of mucus in surrounding tissues

• Seen mainly in young persons; the lips are the favoured site

• Usually appear as small, fluctuant masses—large mucoceles of the floor of the

mouth are known as ranulas; these may extend into the neck

Sialolithiasis

• This is the formation of stones (calculi) in the ducts of salivary glands

• The stones result from the calcification of an intraluminal nidus e.g. dried

secretions or cellular debris—they are composed mainly of calcium phosphate

• Inflammation of the salivary duct and stasis of saliva have been suggested as

predisposing factors—the submandibular duct is the most common site

• Peak incidence in the fourth and fifth decades

• The stones vary in size, surface texture and colour

• Recurrent infection of affected glands (secondary to obstruction) is common

2) Inflammation (Sialadenitis)

• Can be caused mechanical, physical, infectious and immunologic factors:

Mechanical

• Mechanical obstruction of salivary ducts can be intraluminal (e.g. stones) or

extraluminal (e.g. tumours)

• It leads to chronic and recurrent sialadenitis that can result in partial or

complete destruction of the affected gland

Physical

• Physical causes of sialadenitis include radiation e.g. administered during

treatment of head and neck cancers

• Initial acute inflammation is followed by chronic sialadenitis and fibrosis

• Infectious

• Acute suppurative sialadenitis

• Usually caused by Staphylococcus aureus and group A streptococci that enter salivary ducts from the oral cavity: reduced or absent salivation thought to predispose

• Ductal epithelium and acini are destroyed by invading inflammatory cells and microabscesses may form

• Viral sialadenitis

• Several viruses can cause sialadenitis including paramyxovirus (the mumps virus), coxsackieviruses A and B, influenza viruses and cytomegalovirus—of these mumps is the most common to involve the glands

• HIV-associated cysts of the parotid

• HIV infection can cause lymphadenopathy of intraparotid lymph nodes

• There is marked lymphoid hyperplasia which can be accompanied by the formation of keratin-filled cysts (salivary duct epithelium undergoes metaplastic change)

• Unilateral or bilateral enlargement of the parotids can result

• Tuberculosis

• Tuberculosis may involve intraparotid and paraparotid lymph nodes; infection of these nodes may originate from a tuberculous focus in the mouth or pharynx, or result from dissemination of pulmonary TB

• Can present as painless mass/masses mimicking a tumour

• Histologic examination will reveal the typical caseating granulomas and the findings can be confirmed with cultures and special stains

• Immunologic

• Sjogren’s syndrome

• Autoimmune disease characterized by the progressive lymphocytic infiltration and destruction of exocrine glands, particularly the salivary and lacrimal glands

• Clinical hallmarks are keratoconjunctivitis sicca, xerostomia, and rheumatoid arthritis; may also be assoc. with other autoimmune disesases e.g. SLE

• 90% patients are female; average age at diagnosis is 50 yr.

• Firm, diffuse, painless enlargement of the salivary glands, which is usually but not always bilateral, is the typical presentation

• Histologic hallmark is a lymphocytic sialadenitis—lymphoid follicles may be presentThese patients are at increased risk for non-Hodgkins lymphoma

3) Benign Tumours

Pleomorphic Adenoma (Benign mixed tumour)

• Most common salivary gland tumour overall

• Accounts for 60 – 70% of parotid tumours, 40 – 60% of submandibular tumours, and 40 – 70% of minor salivary gland tumours

• Peak incidence between 30 and 50 years; female to male ratio 3:1

• Slowly-growing painless, firm masses—in the parotid, most occur in the superficial lobe

• A variety of growth patterns may be seen histologically—the basic components are epithelium, myoepithelium and stroma .

• Recurrence may occur if the tumour is inadequately excised.

Warthin’s tumour (Papillary cystadenoma lymphomatosum)

• Slow-growing benign tumour that arises almost exclusively in the parotid

• 5 – 6% of parotid tumours; peak incidence 40 – 70 years; male to female ratio is 5:1.

• It is proposed that the tumour develops from parotid ductal epithelium present in lymph nodes within the gland.

• Most tumours measure 2-3 cm at diagnosis; tumours are bilateral in 7% of patients

• The histology is distinctive and pathognomonic—epithelial-lined cystic spaces showing papillary projections are present in a lymphoid stroma.

• As with pleomorphic adenomas, recurrence may occur if the tumour is incompletely removed.

4) Malignant Tumours

• Malignant salivary gland tumours are less common than benign ones; ratio of benign to malignant approximately 4:1

• The most common tumours are mucoepidermoid carcinoma, adenoid cystic carcinoma, acinic cell carcinoma and malignant mixed tumours.

 Mucoepidermoid carcinoma

• Most common malignant salivary gland tumour; accounts for 2-10% of major salivary gland tumours and 10-40% of minor salivary gland tumours

• Most common in 35-65 year age group; however, it can affect children and adolescents

• They are slowly growing firm masses that are often clinically indistinguishable from the more common pleomorphic adenoma, and range in size from 1-4 cm.

• Histologically these tumours are composed of epidermoid cells, mucus-secreting cells and intermediate cells; classified as low, intermediate and high-grade

• The histologic grade is directly related to prognosis—survival rate in patients with low-grade tumours is 90-100%; intermediate and high-grade tumours tend to show local invasion, recurrence, and metastases, with survival rates of 40-60%.

 Adenoid Cystic Carcinoma

• Account for 3-10% of salivary gland tumours— more common in minor salivary glands

• Twenty-five percent arise in major salivary glands, most commonly the submandibular

• May arise at any age, but occur most frequently in the 4^th to 6^th decades

• Patients with tumours in the major glands commonly present with a painful mass. Those in the minor glands can also produce respiratory obstruction

• Usually form well-defined masses, but histologically are seen to infiltrate surrounding tissues

• Perineural invasion is characteristic of this neoplasm, and this feature seems to account for the poor long-term outcome in patients with this tumour.

• Metastasis can occur to cervical lymph nodes or distant sites e.g. lung, bone, liver, brain

• 5-year survival rates as high as 70% have been reported, but rate declines to 5-15% at 20 years.

Acinic Cell Carcinoma

• Relatively uncommon tumour; accounts for 2-3% of salivary gland tumours.

• Most often involves the parotid; most common malignant tumour involving >one salivary gland

• Most common in the 5^th decade

• Range in size from 2-4 cm; most are solid, though cystic change can occur.

• These carcinomas are regarded as low-grade tumours—regional metastasis occurs in 5-10% of patients, but distant metastasis is rare. Five and 10-year survival rates have been reported as 82% and 68% respectively

Category: Pathology Notes