underlying process appears to be a disorder of salivary gland innervation. It is also seen in malnutrition, chronic alcoholism, bulimia, liver cirrhosis and has been linked to some drugs, such as antihypertensive agents .
It is rarely biopsied, but histologically there is enlargement of the serous acinar cells (two or three times the normal size) and slight compression of the duct system by the swollen acini.
5.5.3 Adenomatoid Hyperplasia of Mucous Salivary Glands
This nodular hyperplastic lesion is usually asymptomatic, often being noted on routine dental examination. Most cases occur on the palate, but sometimes other minor glands can be involved . It can affect all ages, although most patients are between 30 and 60 years old. There is a slight male predominance. Examination reveals nodular mucosal swellings up to 30 mm in diameter. The aetiology is unknown, but possible relevant factors include local trauma due to dentures or tobacco smoking. The main histological feature of adenoma-toid hyperplasia is the presence of hypertrophic and hyperplastic mucous lobules of minor salivary glands. Inflammation, fibrosis and cytological abnormality are not usually seen.
farction may be total and squamous metaplasia florid . Possible causes include trauma by the needle  and an increased sensitivity of oncocytic cells to hypoxia .
5.5.4 Irradiation Changes
5.6 Oncocytic Lesions
Oncocytic change is where cells develop intensely eosin-ophilic granular cytoplasm due, to increased numbers of mitochondria .
Salivary glands are very sensitive to radiation, and xerostomia is a common complication. Acute radiation injury of salivary glands manifests with swelling, vacu-olation and necrosis of acinar cells. Initial acute inflammatory response is later followed by chronic sclerosing sialadenitis characterised by loss of acini, focal squamous metaplasia, and fibrosis. When all the salivary glands are involved, the loss of saliva is progressive and irreversible.
Fine needle aspiration (FNA) is an important technique in the investigation of salivary disease, particularly tumours, but the procedure itself can have adverse effects, causing difficulties in histological assessment and even simulating malignancy. The effects are classified as tissue injury with repair, infarction and reactive pseudo-malignant changes . Some or all of these can occur in any tumour  including pleomorphic adenoma, but are most frequent in Warthin's tumour, where in-
Foci of oncocytic metaplasia, usually of ducts, but occasionally also acini, occur with increasing frequency with advancing age (Fig. 5.3). In contrast, diffuse on-cocytosis of the parotid is extremely rare. Microscopic examination shows oncocytic metaplasia of ducts and acini involving virtually the whole gland. As with most other oncocytic lesions, diffuse oncocytosis comprises two types of cells, light and dark. The former are large and round or polygonal and have finely granular, pink cytoplasm and a single vesicular nucleus. The dark cells are usually more sparse and have deeply eosino-philic, compressed cytoplasm and densely hyperchro-matic nuclei.
Oncocytic metaplasia of ducts often with cystic dilation (also known as oncocytic papillary cystadenoma) occurs mainly in the minor glands, particularly the larynx, and
Following Fine Needle Aspiration only occasionally in the parotid (see Sect. 5.8.10). The lesions are often multifocal and usually small, but can reach 30 mm in diameter.
This rare condition consists of nodules of varying size, composed of oncocytic cells, often with relatively clear cytoplasm. The nodules appear to engulf normal acini giving a false impression of invasion, but there is no stromal or other response by the acini. Multifocal nodular oncocytic hyperplasia (MNOH) can be mistaken for a clear cell neoplasm with satellite deposits when one nodule is much larger than the others. MNOH can also be bilateral, and it has been reported to co-exist with a pleomorphic adenoma, which itself showed oncocytic change [20, 158].
lobular architecture, and some lobules are affected more severely than others. The cysts vary in size up to a few millimetres, and they are irregular in shape and often interconnect. The lining epithelium is flat, cu-boidal to low columnar, sometimes with an apocrine-like appearance. The lumen contains secretion with spherical microliths. Remnants of salivary acini are seen between the cysts, and thick fibrous interlobular septa are often prominent.
A mucocele is defined as the pooling of mucus in a cystic cavity . Two types are recognised - extravasation and retention; extravasation mucocele is described in Sect. 5.2.1. Retention cysts can occur at any age, and the mucus pool is within an epithelium-lined cavity, likely to be a dilated excretory duct.
5.6.3 Multifocal Nodular
Non-neoplastic cysts and pseudocysts accounted for about 6% of all lesions of the salivary glands in the Hamburg registry of salivary neoplasms and tumour-like lesions . They can be classified as:
1. Dysgenetic, e.g. polycystic dysgenetic disease;
2. Acquired cysts lined with epithelium, e.g. lympho-epithelial cystic lesions, duct cysts;
3. Pseudocysts without an epithelial lining, e.g. extravasation mucocele, including ranula;
4. Cystic change in neoplasms, e.g. Warthin, variants of mucoepidermoid and acinic cell carcinomas, lymphoepithelial sialadenitis (LESA), lymphoma, and rarely, pleomorphic adenoma;
The commonest are mucoceles, including ranula (80%), parotid duct cysts (11%), lymphoepithelial cystic lesions (7%) and dysgenetic cysts and congenital sialectasia (together 2%).
This very rare condition resembles cystic anomalies of other organs, such as the kidney, liver and pancreas, although no association has been described [62, 172, 177]. Some cases are familial , and almost all cases occurred in females. Most patients present in childhood, but some have not been recognised until adulthood. It only affects the parotid glands, usually bilaterally. Microscopically, the glands maintain their
Salivary duct cysts are acquired, and are due to dilatation of a salivary duct following obstruction, sometimes by a tumour . They can occur at any age, although usually in patients over 30 years old. Most (85%) arise in the parotid and are unilateral and painless. They are well-circumscribed, unilocular and up to 100 mm in diameter (usually 10 to 30 mm). They contain fluid that is watery to viscous brown, occasionally with mucus. The wall comprises dense fibrous tissue, 1-3 mm thick, and there is often mild to moderate chronic inflammation, although not the dense lymphoid infiltrate of a lympho-epithelial cyst. The epithelium is stratified squamous, or a single layer of cuboidal or columnar cells, with occasional goblet cells and oncocytes.
Seven types of salivary lesions can be characterised by single or multiple epithelial-lined cysts surrounded by lymphoid tissue including germinal centres: benign lymphoepithelial cyst and cystic lymphoid hyperpla-sia of AIDS, in addition to Warthin's tumour, LESA and mucosa-associated lymphoid tissue (MALT lymphoma) each with cystically dilated ducts, low-grade cyst-forming mucoepidermoid carcinoma with a heavy lymphocytic response, and cystic metastases in intra-parotid lymph nodes, each of which is discussed in Sect. 5.14.
5.7.1 Salivary Polycystic Dysgenetic Disease
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