Salivary neoplasms (Table 42.5)

  Salivary neoplasms comprise 1.2 per cent of all neoplastic disease. Nearly all salivary neoplasms present as slowly growing masses which have often been present for several years. Even malignant salivary tumours usually grow slowly. Unfortu­nately pain is not a reliable indication of malignancy. Certainly if a malignant salivary neoplasm is invading a sensory nerve pain or paraesthesia can occur but frequently at surgery one sees a nerve macroscopically invaded by tumour but which has been functioning normally pre­operatively. Furthermore benign tumours often present with pain and aching in the affected gland presumably due to capsular distension and possibly also due to an element of outflow obstruction. Therefore the only reliable clinical indication of malignancy is facial nerve palsy in the case of the parotid, induration and/or ulceration of the overlying skin or mucosa and regional lymphatic metastasis.

The investigation of salivary neoplasms

For parotid and submandibular tumours CT and MRI scanning are the most helpful imaging techniques (Figs 42.10 and 42.11). They will confirm that the mass being investigated is indeed intrinsic to the gland, they accurately image the borders of the tumour and show whether it is well circumscribed and benign or diffuse, invasive and malignant. In addition they show the relationship of the tumour to other anatomic structures and help with the planning of subsequent surgery.

Open surgical biopsy of intrinsic neoplasms of the major glands is absolutely contraindicated. At least 75 per cent of all parotid tumours and more than 50 per cent of all submandibular gland tumours will prove to be benign pleomorphic adenomas. This tumour which is only poorly encapsulated is very tense and if an incision is made into it the contents of the tumour burst into the surrounding tissue planes and it is impossible to eradicate the microscopic spillage of tumour cells. If this happens the patient will develop multiple local tumour recurrences over many years unless they are subjected to radical postoperative radiotherapy, which is best avoided in the management of benign disease. Clearly if there is skin infiltration or ulceration an open biopsy is essential to establish a preoperative diagnosis upon which to plan surgery. For tumours of the minor salivary glands particularly in the palate there is a much higher chance of the tumour being malignant and as it is not necessary to open up other tissue planes to gain access to the tumour as open incisional biopsy is important.

Fine needle aspiration (FNA) biopsy is a safe alternative to open biopsy of a major gland. Evidence suggests that provided the needle gauge does not exceed 18 G there is no risk of seeding viable tumour cells. Although advocates of this tech­nique claim high accuracy and specificity, there is inevitably a high risk of sampling error.  

Epithelial tumours

 

Seventy-five per cent of all salivary epithelial tumours arise in the parotid glands and, of these, only 15 per cent are malignant. Just over 10 per cent occur in the submandibular glands and, of these, approximately one-third are malignant. About 15 per cent of tumours occur in the minor salivary glands and nearly half of these will be malignant. Tumours arising in the sublingual glands are rare (0.3 per cent) but nearly all of them will be malignant. Both benign tumours — adenomas — and malignant tumours

       carcinomas — occur.

  Adenomas

 

Of the variety of benign adenomas that has been described only two — the pleomorphic adenoma and Warthin’s tumour —arise with any frequency.

The pleomorphic adenoma occurs at any age (mean 42 years) and has an equal sex incidence. It accounts for at least 75 per cent of parotid tumours and more than 50 per cent of submandibular tumours. It accounts for rather less than 50 per cent of minor gland tumours. Clinically the tumour has the texture of cartilage and has an irregular and bosselated surface. In the palate, the overlying mucosa is rarely ulcerated. Very rarely after a number of years the tumour may undergo malignant change and for this reason all patients presenting with pleomorphic adenomas should be advised to undergo surgical removal of the tumour (Fig. 42.12).

The Warthin’s tumour occurs only in the parotid gland where it accounts for approximately 15 per cent of all neoplasms. It is a disease of the elderly with a mean age of presentation of 60 years. Historically it had a male:female ratio of 4:1 but it is now becoming increasingly common in females. Recent evidence suggests that this tumour is related to cigarette smoking. It is also unusual in that in

10 per cent of cases it arises either bilaterally or is multicentric in the one gland. It does not undergo malignant change.

 

Carcinomas

 

The acinic cell carcinoma and the mucoepidermoid carcinoma, although undoubtedly malignant tumours with a potential for local invasion and metastatic spread, are frequently very low grade histologically and do not require the radical treatment needed for more aggressive tumours. Together they account for only 5 per cent of all tumours at any sire. The mucoepidermoid tumour is much more common in the USA where it forms 10 per cent of all salivary neoplasms.

The adenoid cystic carcinoma, adenocarcinoma, squamous cell carcinoma and undifferentiated carcinoma are all aggressive malignant tumours that carry a poor prognosis regardless of treatment. The adenoid cystic carcinoma is characterised by relentless perineural spread along the cranial nerves and into the brain. However, it grows extremely slowly and although inevitably fatal the 5- and 10-year survival figures are 70 per cent and 40 per cent, respectively. It is also unusual in having a predilection for distant metastasis to the lungs where it produces often multiple cannon ball tumours which remain symptomless for many years. The other carcinomas mentioned above have 5-year survival figures of around 25—35 per cent.

 

Management of epithelial tumours

 

Both benign and malignant tumours arising in the parotid or submandibular glands are treated surgically by excision with surgical clearance. In the parotid gland this is by either superficial or total parotidectomy according to the location of the tumour. Unless the patient presents with facial nerve palsy (indicating a malignant tumour) the facial nerve is always preserved. In the submandibular gland treatment is always by excision of the gland. If when a definitive patho­logical diagnosis is received the tumour is malignant then the patient should receive radical postoperative radiotherapy. In those cases when the tumour involves skin or other adjacent structures or where there is lymphatic metastasis the patient should undergo radical excision, including a neck dissection and sacrificing any structures invaded by tumour, and again treated with postoperative radiotherapy.

Pleomorphic adenomas arising in the minor salivary glands can be treated by local excision with a 5-mm margin. They do not invade periosteum and so in the palate they should be excised subperiosteally. Mucoepidermoid carcinomas and acinic cell carcinomas require rather more radical excision with a 10-mm margin and, when they are situated in the palate, palatal fenestration should be undertaken. Postoperative radiotherapy is only indicated for high-grade tumours or if the margins are not clear. For the remaining carcinomas arising in the minor salivary glands radical surgical excision and postoperative radiotherapy are indicated. In the palate this will be by maxillectomy.

 

Nonepithelial tumours

A variety of nonepithelial tumours can arise in the salivary glands. Haemangiomas and lymphangiomas (cystic hygromas) occur in childhood. Haemangiomas occur mostly in the parotid and appear shortly after birth and grow progressively for several months. The majority undergoes spontaneous regression by 2 years of age. Females are more frequently affected. Lymphangiomas are less common. They may affect any of the salivary glands. They form sponge-like multicystic lesions. Fifty per cent are manifest by 12 months and 90 per cent will be evident by the end of the second year. They do not undergo spontaneous involution. They frequently extend into the neck and mediastinum, and can undergo dramatically rapid growth causing respiratory obstruction. Treat­ment is by complete surgical excision but this may be technically very difficult.

Neurofibromas and neurilemmomas are the commonest nonepithelial tumours arising in adults. Clinically they are

nor distinguishable from other salivary tumours and are only diagnosed following surgery for a presumed epithelial tumour. Lipomas occur in the parotids particularly in adult males. They are treated by surgical excision.

 

Malignant lymphomas

True extranodal lyrnphoma arising in the salivary glands —usually the parotids — is rare. More common is lymphoma arising from the lymph nodes either on the surface of the glands or within the parenchyma of the gland. Lymphoma also arises in the salivary glands, as a complication of HIV disease, and also in benign lymphoepithelial lesion and Sjogren’s syndrome. The peak incidence for nonHodgkin’s lymphoma is the sixth and seventh decades and females are twice as likely as males to be affected.

Salivary gland lymphomas usually present as firm painless swellings and more than 90 per cent occur in the parotids. If the lymphoma is confined to the parotid, treatment is by parotidectomy with postoperative radiotherapy. If there is evidence of spread beyond the salivary gland, treatment is by polychemotherapy according to the accepted protocols based on histological characterisation.

 

Unclassified and allied conditions

Sialosis is an uncommon noninflammatory cause of salivary swelling usually affecting the parotid glands symmetrically. It is usually associated with metabolic and endocrine conditions such as alcohol abuse, diabetes mellitus, pregnancy, malnutrition and some drugs (usually sympathomimetics). It usually affects middle aged and elderly adults who present with bilateral soft parotid swellings. Biopsy of the glands reveals extensive fatty replacement but otherwise normal tissues. No treatment is known to be effective but sometimes parotidectomy is required to correct the disfigurement.

Necrotising sialometaplasia, benign lymphoepithelial lesion, salivary duct cysts, Kuttner tumour and cystic lym­phoid hyperplasia of HIV disease can all mimic salivary gland neoplasia. Similarly, branchial cysts and dermoids can present diagnostic confusion on occasion. As has already been dis­cussed both sarcoid and toxoplasmosis can present as parotid pseudotumours.