Salivary Gland Tumours

Anatomy of Salivary Gland Tumours

The "salivary glands" develop during weeks 6-8 of gestation to form the parotid, submandibular, sublingual and minor salivary glands.

Parotid:

• Serous acini primarily
• deep and superficial lobes separated by the facial nerve, and tail.
• Surrounding fascia is a continuation of deep cervical fascia
• Stensen's duct: anterior border to 2nd maxillary molar.

Submandibular

• In submandibular triangle
• Mucous & Serous Acini
• Wharton’s Duct into the anterior floor of the mouth.

Sublingual

• In the anterior floor of the mouth
• Multiple ducts of Rivinus form Bartholin's duct, which empties into Wharton's duct.

Minor glands

• Common locations include labial, buccal, palatine, anterior and posterior lingual. There are over 600 - 1000.
• Mainly mucous secreting

Classification of Salivary Gland Tumours

Salivary gland tumours can arise from epithelial, mesenchymal and lymphoid tissue.

The major and minor salivary glands are associated with a remarkable diversity of neoplasms. WHO histologic classification for salivary gland tumours has over 40 different types of tumours as they can arise from epithelial, mesenchymal and lymphoid tissues. There were recent updates in their 8th edition publication on Salivary Gland Tumours.

From a clinical perspective, salivary gland tumours can be classified by the type of gland and their degree of malignancy.

Type of Gland

The most common location of a salivary gland tumour is the parotid gland but it does have the least risk of malignancy.

• Major salivary gland: parotid, submandibular, sublingual.
• Minor salivary gland: small glands throughout the head and neck region.

Disease

These are just some examples of the 40+ different types of salivary gland tumours.

• Benign: pleomorphic adenoma, adenolymphoma, oncocytoma, sebaceous neoplasms, intraductal papilloma.
• Benign Soft Tissue: Haemangioma (commonest paediatric salivary gland tumours), Lipoma, sialolipoma, nodular fasciitis.
• Malignant: mucoepidermoid, adenoid cystic, acinic cell, mixed, adenocarcinoma (from myoepithelium), primary SCC, sebaceous, lymphoma.
• Non-neoplastic epithelial: sclerosing polycystic adenosis, nodular oncocytic hyperplasia, lymphoepithelial sialadenitis, intercalated duct hyperplasia.
• Hematolymphoid: mucosa-associated lymphoid tissue (MALT lymphoma).

Benign Salivary Gland Tumours

Benign tumours are the most common type of salivary gland tumours. The two most frequently diagnosed are pleomorphic adenoma (commonest solid tumour in children) and adenolymphoma. Less common benign tumours include intraductal papilloma, sebaceous neoplasms and oncocytoma.

Typically, they present as a painless, slow-growing mass. There are several different types, and here are some examples below.

Pleomorphic Adenoma

• Incidence: most common salivary tumour & often in middle-aged females.
• Pathology: benign mixed tumour with a low malignant potential (~10%)
• Location: often parotid (esp. superficial lobe tail), less likely submandibular.
• Surgery: superficial parotidectomy or total parotidectomy if deep lobe with facial nerve preservation or total resection of a non-parotid salivary gland resection. Tumour is not encapsulated, which means simple enucleation would result in high recurrence rates.
• Radiotherapy: No role for radiotherapy.

Adenolymphoma (Warthin's Tumour)

This condition can also be referred to as papillary cystadenoma lymphomatosum.

• Incidence: ~20% of salivary tumours & often in middle-aged smoking males
• Pathology: epithelial and lymphoid components with abundant cystic spaces
• Location: nearly always in the parotid, ~10% are bilateral & multicentric.
• Treatment: superficial or deep parotidectomy with facial nerve preservation  

Malignant Salivary Gland Tumours

Malignant salivary gland tumours can be primary or secondary malignancies (less common) with different histopathological grades (high, low or mixed). They are most commonly found in the parotid gland and less so in the submandibular gland.

Clinical features of salivary gland malignancy include pain, facial nerve palsy, rapid growth, obstructive symptoms or local invasion.

The most common salivary gland tumours are mucoepidermoid carcinoma (also in children), followed by adenoid cystic carcinoma and acinic cell carcinoma. Less common malignancies include adenocarcinoma, primary SCC, sebaceous carcinoma and lymphoma.

Mucoepidermoid Carcinoma

• Incidence: commonest parotid malignancy, middle-aged males & females.
• Pathology: variable malignant potential based on histological grade, contains mucus-secreting cells, and epithelial cells of the epidermoid variety. It arises from the excretory duct.
• Location: usually in the superficial lobe of the parotid.
• Treatment: consider adjuvant radiotherapy, parotidectomy, neck dissection.

Adenoid Cystic Carcinoma

This is the most common malignancy of the sublingual, submandibular and minor salivary glands (mucoepidermoid carcinoma is the second commonest)

• Incidence: in middle-aged and elderly males and females.
• Pathology: cribriform (Swiss-cheese, better prognosis), tubular (low grade), solid (high grade). It arises from the intercalated duct.
• Location: usually in the submandibular gland.  
• Treatment: adjuvant radiotherapy, resection, high recurrence risk.

Acinic Cell Carcinoma

• Incidence: in middle-aged patients
• Pathology: usually a low-grade multifocal tumour (once considered benign!) arising from the acinus.
• Location: occurs most often in the parotid gland
• Treatment: Total parotidectomy; radiotherapy has no role.

Investigations of Salivary Gland Tumours

The diagnosis of salivary gland tumours is based on history, examination findings and investigative results. Investigations to consider are:

1. Fine Needle Aspiration for Cytology: benign vs malignant  
2. Ultrasound: guides FNAC, assess location and lymph nodes
3. CT or MRI: anatomical location, staging for metastasis
4. Open Biopsy: can cause tumour seeding

A differential diagnosis for a parotid gland swelling can include the aforementioned benign and malignant tumours, and also:

• Sialadenitis: chronic swelling independent of eating.
• Sialolithiasis: recurrent pain and swelling with eating. It is the most common cause of submandibular swelling and can be diagnosed with a Sialogram.
• Granulomatous disease: sarcoid, actinomycosis, mycobacterium
• Transient glandular hypertrophy (bulimics)

AJCC Staging

• T1: <2 cm without extraparenchymal extension
• T2: 2-4 cm without extraparenchymal extension
• T3: >4 cm and/or having extraparenchymal extension
• T4: >6 cm or extension into extraglandular tissues
• T4a: Invades skin, mandible, ear canal, or facial nerve
• T4b: Invades skull base, pterygoid plates, carotid artery

Neck dissection is indicated for malignant salivary gland tumours with clinically positive nodes detected either on physical examination or with preoperative imaging workup.

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