Salivary Gland Neoplasms

Question 1

Where do most salivary gland neoplasms arise

Answer 1

• Parotid
• But also frequent in intraoral minor glands making them the second most common neoplasm of the mouth after squamous cell carcinoma

Question 2

What is the aetiology of salivary gland neoplasms

Answer 2

• Can result from irradiation to the head e.g. head and neck cancer
• Several salivary tumours are known to be caused by specific fusion genes. (arise from chromosomal breakage during mitosis, the fragments rejoin incorrectly as chromosomal translocations, deletions or inversion)

Question 3

How do salivary gland tumours present clinically

Answer 3

• Salivary neoplasms al most always present as a mass, sometimes with added symptoms of obstruction if the excretory duct is compressed
• Key symptoms to elicit in the history are those of nerve involvement. Facial nerve signs almost certainly indicate that a parotid mass is a malignant neoplasm

Question 4

What percentage of salivary gland tumours are intraoral minor glands, parotid, sublingual and submandibular?

Answer 4

10% intraoral minor glands
78% parotid glands
0.3% sublingual glands
12% submandibular glands

Question 5

Difference in clinical features between benign and malignant salivary gland tumours (speed of growth, consistency, location, ulcerations, associated nerve signs)

Answer 5

1. speed of growth
   - Benign: slow-growing
   - Malignant: Some are fast-growing and painful, but many are slow-growing and asymptomatic
2. Consistency
   - Benign: Soft or rubbery
   - Malignant: Sometimes hard consistency
3. Location
   - Benign: 85% of parotid tumours
   - Malignant: 45% of minor gland tumours
4. Ulceration
   - Benign: no
   - Malignant: May ulcerate and invade bone
5. Associated nerve signs
   - Benign: no
   - Malignant: May cause cranial nerve palsies, usually lingual, facial or hypoglossal depending on the site

Question 6

What investigations need to be done for salivary gland tumours

Answer 6

• Tx depends on tumour type and extent
• Key investigation is fine needle aspiration (can often determine whether neoplasms are benign or malignant, low or high grade, or can be used to narrow down a differential diagnosis
• Most neoplasms in the superficial parotid gland are amenable to FNA and ultrasound guidance can be used to target more deeply seated tumours
• Imaging for suspected salivary neoplasms are best performed by MRI. It can detect perineurial spread and base of skull invasion by palatal and parotid cancers
• CBCT is useful to detect palatal bone perforation below palatal tumours
• Sialography no longer has any role in investigation of salivary neoplasms
• Ultrasound scan to differentiate salivary neoplasm from enlarged intraparotid lymph nodes

Question 7

What are the benign salivary tumours?

Answer 7

• Pleomorphic adenoma

- Warthin’s Tumour

Question 8

What are the clinical features of pleomorphic adenoma

Answer 8

• Characterised by usually broad range of tissue types
• Commonest slaivary tumours (75% of parotid tumours and 20% of submandibular and 20% of intraoral minor gland tumours)
• Arise any age but most common in middle age
• Grow slowly and take several years to reach 2cm
• Circumscribed, with capsule around most of the periphery (never complete)
• Rubbery, firm swellings, smooth when small but often very lobulated when large (when tumour grows, it pushes out larger finger-like extensions or bulges out to form lobulated outline)
• Overlying skin or mucosa is mobile over the lump, although in the palate the more inflexible mucoperiosteum may appear fixed

Question 9

What is the histology of pleomorphic adenoma

Answer 9

• Capsule: can be thick but almost never complete
• Neoplastic cells from ducts, small cysts and sheets
• Sheets and strands of epithelial cells
• Cells at periphery of sheets detach and secrete matrix proteoglycans
• Dispersed cells in matrix form ‘myxoid’ stroma
• Myxoid storma may develop into cartilage which may ossify to from bone rarely
• Mixture of epithelial and CT types accounts of the old name ‘mixed tumour’

Question 10

What is the aetiology of pleomorphic adenoma

Answer 10

• Chromosomal translocation that activates one of two genes, PLAG1 or HMGA2
• These encode transcription factors important in normal development
• Their activation results in cell proliferation and abnormal differentiation, explaining the varied tissues formed
• In addition, can have other chromosomal abnormalities involving oncogenes and tumour suppressor genes. This increase with time and probably account for the risk of malignant transformation in longstanding tumours

Question 11

What is the management of pleomorphic adenoma

Answer 11

• Excision with a margin of normal tissue
• Risk of recurrence: if the capsule is disrupted and some contents leaks out leads to widespread recurrence in the tissues (most problematic for parotid tumours, where spillage of gelatinous tumour into facial planes of the neck and seed multiple nodules of tumour in tissues from base of skull down to clavicle
• Tumours in deep love require complete parotidectomy
• If in submandibular gland whole gland is removed
• Recurrence is often multifocal - difficult to eradicate from surgery
• Longstanding examples regardless of size occasionally undergo malignant change

Question 12

What are the clinical features of Warthin’s tumour

Answer 12

• Close association with heavy smoking, particularly in multifocal tumours
• Develop in salivary glands, lymph nodes and in the upper third of the deep cervical lymphatic chain
• The lymph node tumours are not metastatic but arise from developmental rests of salivary gland ducts that are commonly found in lymph nodes at these sites

Question 13

What is the histology of Warthin’s tumours

Answer 13

• Tumour is a cyst or part solid part cystic mass with a thin capsule
• Characteristic histological appearance with a lymphoid and an epithelial component
• Lymphoid tissue resembles lymph node: lymphoid follicles and germinal centres
• Epithelial cells are tall, eosinophilic columnar cells
• Abnormal large distorted mitochondria almost completely fills the cells => referred to as oncocytes

Question 14

What is the aetiology, diagnosis and management of Warthin’s tumour

Answer 14

Aetiology
- Cause may be defects of mitochondrial genes

Diagnosis
- FNA

Management

• Cured by simple excision
• 15% recurs

Question 15

What is a key clue to malignancy of salivary gland

Answer 15

• Matt are low-grade carcinomas, with slow growth and a clinical presentation that can be identical to that of benign neoplasm
• Key clue to malignancy is recognising how the risk of a salivary neoplasm being malignant varies between sites. Most types present as a firm mass, but some are aggressive and present with classic assigns of malignancy: fixation to adjacent tissues, nerve signs, ulceration, bleeding, bone erosion or metastasis to germinal lymph nodes
• Trismus may result from infiltration of MoM when carcinomas arise in the parotid, soft palate and retromolar area

Question 16

How are malignant salivary tumours diagnosed

Answer 16

• Diagnosis depends on histological examination.
• High grade neoplasm are recognised on FNA
• Lower grade types can only be diagnosed after excision
• Therefore, envision of any alsivaty mass without a diagnosis after FNA and imaging must be undertaken on the assumption that it may turn out to be malignant

Question 17

How are malignant salivary tumours treated

Answer 17

• Treated by surgical excision followed by radiotherapy if excision is incomplete or margins close
• Recurrence is often difficult to manage; minor gland re-excision may require resection of facial skin, and parotid gland re urgencies may involve the base of skull and infratemporal fossa

Question 18

What are the types of malignant salivary gland tumours

Answer 18

• Mucoepidermoid carcinoma
• Adenoid cyst carcinoma
• Polymorphous adenocarcinoma
• Acinic cell (adeno) carcinoma
• Carcinomas ex pleomorphic adenoma

Question 19

What are the clinical features of Mucoepidermoid carcinoma

Answer 19

• Most common single type of malignant salivary neoplasm but only accounts for <10% of salivary gland neoplasms
• About half arise in the parotid gland, but all gland including minor glands can be affected
• The carcinomas usually contain mucin-filled cysts and are easily mistaken clinically for mucous extravasations or retention cysts when they develop in minor glands
• Tumour is usually grows slowly and infiltrates into surrounding tissues

Question 20

What is the aetiology and treatment of mucoepidermoid carcinomas

Answer 20

Aetiology
- Translocation brings MECT1 with MAML2 gene => produces fusion gene => activates the notch signalling pathway, an important developmental pathway that is deranged in several types of cancer

Tx
- Wide excision

Question 21

How are mucoepidermoid carcinomas diagnosed

Answer 21

• Histological examination
• The cysts are lined by epithelium that resembles skin epithelium and is therefore called epidermoid
• It has basal and prickle cells but does not keratinise. Scattered in the epidermoid sheets and cyst linings are variable numbers of mucin-secreting goblet cells
• Two cell types give the name ‘mucoepidermoid’. Either mucous or epidermoid cells may predominate

Question 22

What are the clinical features of adenoid cystic carcinoma

Answer 22

• Unusual behaviour and poor outcome
• Most arise in major glands, usually parotid. Can also arise in minor glands and in mucous glands in the nose, antrum and throughout the mucosa of the aerodigestive tract
• Grow slowly and have peculiar propensity to invade nerves - ‘perineurial spread’
• Perineural spread can produce unusually sensory symptoms, pain or facial weakness and occasional pts present with these symptoms rather than a mass
• Can extend several cm along nerves beyond clinical apparent mass
• Carcinomas in palatal glands or parotid are sometimes found to have reached the brain at presentation

Question 23

What is the aetiology, histology and diagnosis of adenoid cystic carcinoma

Answer 23

Aetiology

• Translocation fusing the proto-oncogene myb with the transcription factor gene NFIB => fusion protein
• Carcinoma overexpose myb protein

Diagnosis

• FNA, biopsy after excision
• Immunohistochemically detect myb protein

Histological

• Highly characteristic pattern
• Rounded groups of small darkly stained cells of almost uniform size, surrounding multiple small clear spaces (cribriform or ‘Swiss cheese’ pattern)
• Small ducts lie in the sheets of epithelium

Question 24

What is the prognosis of adenoid cystic carcinoma

Answer 24

• Poor
• Some small or well-circumscribed tumours are effectively excised
• Large tumours and those with perineurial spread and diffuse infiltration through bone and soft tissues are difficult or impossible to excise despite extensive surgery
• Post-op radiotherapy is usually given but not relied on as radio-resistant
• Slow growth means that 1/3 pts survive 5 years but outcome is ultimately fatal
• 1/3 pts develop blood-borne metastases in lung, liver or bone