5.1.1 Normal Salivary Glands
The salivary glands include paired major glands (parotid, submandibular and sublingual) and minor glands throughout the upper aerodigestive tract.
The cellular component comprises serous and mucous acinar and ductal epithelial cells, myoepitheli-al cells and connective tissue components (e.g. fat, fibrous tissue, nerves and blood vessels). The parotid glands consist of predominantly serous acini, the submandibular glands of mixed, serous and mucous acini, while the sublingual glands contain mainly mucous acini. Minor salivary glands also have mixed serous and mucous acini in varying proportions.
Of particular interest are the myoepithelial cells. They are a normal constituent of the major and minor salivary glands, and are believed to have contractile properties that assist in the secretion of saliva. Similar cells are also found in the breast, tracheo-bronchi-al and sweat glands. They are plentiful in the salivary acini and intercalated ducts, but much less so in the larger excretory ducts of the major glands. Microscopic examination shows that myoepithelial cells are thin and spindle-shaped and situated between the basement membrane and epithelial cells, and ultrastruc-turally they are seen to possess a number of cytoplas-mic processes that extend between and over the acinar and ductal lining cells. They display features of both smooth muscle and epithelium, such as numerous microfilaments with focal densities in the cytoplasmic processes, and desmosomes that attach the myoepithelial to the epithelial cells . Similarly, immuno-histochemistry shows that myoepithelial cells stain strongly with alpha smooth muscle actin (aSMA), cal-ponin, smooth muscle myosin heavy chain (SMMHC) , h-caldesmon , S-100 protein  as well as with some cytokeratins (e.g. subtype 14). Maspin, p63 [8, 166] and CD 10 [143, 183] have recently been described as markers of breast myoepithelial cells, and may have a role in identifying their salivary equivalents. Preliminary studies show that p63 may well have practical value . Scattered nests of sebaceous cells can be seen in normal parotid and minor salivary glands .
Serial sectioning has shown an average of 20 lymph nodes within each parotid , and they may be affected by inflammatory processes and neoplasms, both primary and metastatic. Their presence may hamper histologic evaluation of parotid gland lesions .
5.1.2 Developmental Disorders
Agenesis, aplasia, hypoplasia and atresia of the main ducts are all extremely rare. In contrast, intra-parotid nodal heterotopias are very common , and epithelial tumours may arise from them . Extranodal heterotopia is rare, and can be subdivided into high (involvement of the ear, pituitary, mandible, etc.) or low forms (lower neck, thyroid).
Accessory parotid glands comprising salivary tissue separate from the main gland, adjacent to Stenson's duct, are found in 20% of people.
5.2 Obstructive Disorders
This forms an extravasation mucocele, which is defined as the pooling of mucus in the connective tissue in a cavity not lined with epithelium. Most patients are under 30 years of age, and the minor glands are most often affected. The incidence by site is lower lip 65%, palate 4%, buccal mucosa 10%, and (in the major glands) parotid 0.6%, submandibular 1.2% and sublingual 1.1%. The pathogenesis is traumatic severance of a duct, leading to mucus pooling. It presents in the lip as a raised, often blue, dome shaped swelling of the mucosa, usually 2-10 mm in diameter, but it is generally larger in the sublingual gland in the floor of the mouth where it is known as a ranula. Microscopy shows a well-defined mucin-filled cavity lacking an epithelial lining, but lined with granulation tissue and macrophages (Fig. 5.1).
5.2.2 Chronic Sclerosing
(Atrophic) Sialadenitis of the Submandibular Gland (Kuttner Tumour)
In most if not all cases, this is secondary to calculi in the excretory ducts of the major salivary glands, particularly the submandibular gland. It can occur at any age, though the mean is 44 years. Patients present with pain and/or swelling associated with eating. Histology shows acinar atrophy and a chronic inflammatory infiltrate of variable intensity, but it can be heavy with lymphoid germinal centre formation. The end stage of destruction of the lobular architecture and scarring has been described as salivary gland cirrhosis .
5.5 Miscellaneous Non-Inflammatory Disorders
5.3.1 Bacteria, Fungi
Tuberculosis may involve the gland itself or intra-pa-rotid lymph nodes, and may present as a salivary mass. Other granulomatous infections such as cat-scratch, fungus, sarcoid, leprosy, syphilis, tularaemia, Brucella or toxoplasmosis can also occur in the salivary glands.
Several viral diseases lead to infiltration by chronic inflammatory cells, but are rarely biopsied. This is especially true of mumps, and also in Cytomegalovirus infection, which may involve the salivary glands as part of a systemic infection in either the newborn or immuno-compromised adults, particularly those with AIDS. The diagnosis is made by finding the characteristic enlarged cells with intranuclear inclusions . Other viral infections include Epstein-Barr Virus (EBV), Coxsackie virus and influenza virus, as well as human immunodeficiency virus (HIV). Several lesions may be seen in the salivary glands in patients with AIDS, in particular cystic lymphoid hyperplasia (see Sect. 184.108.40.206).
5.5.1 Necrotising Sialometaplasia (Salivary Gland Infarction)
Necrotising sialometaplasia (salivary gland infarction), is a benign, self-healing lesion, affecting especially the minor glands of the palate. Some cases follow surgery (about 1-8 weeks postoperatively) or even relatively minor trauma, such as from an ill-fitting denture, but often no predisposing factor is known, although the underlying process is generally considered to be ischaemic . Microscopy shows lobular coagulative necrosis of acini (particularly in the early stages), squamous metaplasia of ducts, a chronic inflammatory cell infiltrate and pseu-doepitheliomatous hyperplasia of the overlying surface . There is a superficial resemblance to either muco-epidermoid or squamous cell carcinoma, but the overall lobular architecture of the involved gland is preserved. A similar reaction can be seen in the major glands after surgery or radiotherapy (Fig. 5.2) .
There are a variety of non-infectious inflammatory conditions such as sarcoidosis , Rosai-Dorfman disease , xanthogranulomatous sialadenitis, amyloidosis  and Kimura's disease . They will not be discussed here.
Sialadenosis  is a non-inflammatory process of the salivary glands due to metabolic and secretory disorders of the gland parenchyma accompanied by recurrent painless bilateral swelling of the parotid glands. The peak ages are the fifth and sixth decades . It has been related to endocrine disorders (diabetes mellitis, ovarian and thyroid insufficiencies) as well as autonomic nervous system dysfunction; the
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