Neoplastic Conditions

Pleomorphic salivary adenoma: the commonest tumour with peak prevalence in second and third decades but occurs in all ages even in the newborn. Common in the parotid, palate and upper lip. Histologically, "pleomorphic" describes the architecture not the nuclear morphology. There is an incomplete capsule, a mixture of ducts, sheets of epithelium and myxoid matrix that may in areas resemble cartilage. Locally, recurrence may follow incomplete excision, especially if "shelled out" or if the capsule ruptures. Malignancy can occur in a pleomorphic adenoma but usually only after many years. Rare examples can metastasise to lymph nodes, lung, liver or bone. This so-called (benign) metastasisingpleomorphic adenoma resembles the usual variant although there is usually a history of previous surgery suggesting vascular implantation as a major factor.

Warthin's tumour: occurs at the lower pole of parotid and may be bilateral. More often seen in males and usually older patients. Never in a minor gland and rare in submandibular gland. Probably represents a form of epithelial proliferation of entrapped epithelial elements in a lymph node. Histologically, very distinctive with multiple papillary projections of altered ductal epithelium into cystic spaces containing debris. Many lymphocytes in the stroma with germinal centres, hence the older term "papillary cystadenoma lymphomatosum". Benign; behaves like a lymph node in that other tumours may metastasise to a Warthin's tumour.

A number of other benign tumours can arise in the salivary glands. The term "monomorphic adenoma" has been abandoned since any salivary adenoma that is not a pleomorphic adenoma is a monomorphic adenoma. All are uncommon and include basal cell adenoma, canalicular adenoma, myoepithelioma (a variant of pleomorphic adenoma), oncocytoma and a variety of ductal papillomas and sebaceous adenomas.

Malignant tumours: are relatively uncommon. There are many different types, most are low grade although some are aggressive malignancies that metastasise widely. Males and females are affected equally; there is a wide age range, peak prevalence in 40-50 years but tumours in elderly patients are often high-grade cancers. Most patients have no known risk factors although increased incidence of salivary gland malignancy can follow head and neck irradiation or a long-standing untreated/recurrent benign tumour (e.g., pleomorphic adenoma). Infection by Epstein-Barr virus is linked with lymphoepithelial carcinoma in the Inuit.

Adenoid cystic carcinoma: common in the parotid gland and in minor glands, especially in the palate. Clinically, it is often very subtle; minor gland lesions are soft diffuse and purple mimicking a dental abscess while parotid lesions produce unusual signs like pain, facial paralysis or trismus before there is a palpable mass. Histologically, it has a classical "Swiss cheese" appearance with cribriform clusters of small darkly staining epithelial cells without much nuclear pleomor-phism, mitotic activity or necrosis. Up to half display perineural invasion but this is only significant if it extends beyond the invasive front. Local spread is often extensive; because the tumour evokes no response from the tissues through which it infiltrates, it extends for considerable distances beyond what is identified clinically as the edge. Survival for 10 years is common but patients are often troubled by persistent local disease. Metastasis is via haematogenous routes (e.g., to lung) rather than to nodes.

Mucoepidermoid carcinoma: common in minor glands, especially in the palate, and the parotid gland. It is the commonest salivary tumour in children. Histologically, a mixture of goblet cells, squamous cells and other populations such as intermediate cells or clear cells; may be solid, cystic or both. Histology is little guide to prognosis although tumours with a poor prognosis tend to be large, solid rather than cystic, predominantly epidermoid in type, are infiltrative and cytologi-cally pleomorphic with necrosis and many mitotic figures. Only 10% metastasise, usually after multiple recurrences or if cytologically aggressive and usually to nodes.

Acinic cell carcinoma: uncommon in minor glands; 95% occur in the parotid gland. Histologically, lobulated masses of benign-looking epithelial cells with abundant cytoplasm resembling the serous cells of salivary gland. Populations of other cells are present in varying proportions, e.g., clear cells, cells with vacuolated cytoplasm, ductal cells and/or cells of non-specific glandular type. Low-grade malignancy with nodal metastasis late (especially after recurrences rather than at presentation) in 10%.

Polymorphous low-grade adenocarcinoma: only found in minor salivary glands. Characterised by variable morphological patterns (papillae, cysts, solid areas, cribriform areas, tubular/ductal areas), cytological uniformity (cells often have clear nuclei) and indolent behaviour. Perineural and perivascular whorling is a characteristic feature. Can recur locally if incompletely excised; spread to regional nodes in 10%.

Carcinoma ex pleomorphic adenoma: malignant change may occur in pleomorphic adenoma but usually only in long-standing lesions in major glands. However, being increasingly recognised in minor glands, sometimes without the long history. Rapid enlargement of a long-standing lump, pain or VII nerve palsy and fixation to skin or deeper structures are common findings. Histologically, the commonest finding is a poorly differentiated adenocarcinoma overrunning an old pleomorphic adenoma. Often, there is a mixture of different salivary type carcinomas. Survival is related to the type of the carcinomatous component and the extent of invasion beyond the capsule of the pleomorphic adenoma, so that the prognosis for some patients with minimally invasive and/or histologically low-grade lesions might not be so bad.

Other salivary gland malignancies include epithelial-myoepithelial carcinoma, basal cell adenocarcinoma, hyalinising clear cell carcinoma and MALT lymphoma (low grade), myoepithelial carcinoma (intermediate grade), salivary duct carcinoma, adenocarcinoma NOS, small cell undifferentiated (neuroendocrine) carcinoma, lymphoepithelial carcinoma and primary squamous cell carcinoma (all high grade). Metastatic tumours are not rare in the parotid region; nodal deposits usually derive from squamous cell carcinoma or malignant melanoma in the scalp or facial skin while intraparenchymal deposits usually represent haematogenous dissemination of tumour from sites outside the head and neck.

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