Pathology of the Head and Neck

132 S. Di Palma · R.H.W. Simpson · A. Skalova · I. Leivo5.1 Introduction5.1.1 Normal Salivary Glands5The salivary glands include paired major glands (parotid,submandibular and sublingual) and minor glandsthroughout the upper aerodigestive tract.The cellular component comprises serous and mucousacinar and ductal epithelial cells, myoepithelialcells and connective tissue components (e.g. fat, fibroustissue, nerves and blood vessels). The parotidglands consist of predominantly serous acini, the submandibularglands of mixed, serous and mucous acini,while the sublingual glands contain mainly mucousacini. Minor salivary glands also have mixed serousand mucous acini in varying proportions.Of particular interest are the myoepithelial cells.They are a normal constituent of the major and minorsalivary glands, and are believed to have contractileproperties that assist in the secretion of saliva. Similarcells are also found in the breast, tracheo-bronchialand sweat glands. They are plentiful in the salivaryacini and intercalated ducts, but much less so in thelarger excretory ducts of the major glands. Microscopicexamination shows that myoepithelial cells are thinand spindle-shaped and situated between the basementmembrane and epithelial cells, and ultrastructurallythey are seen to possess a number of cytoplasmicprocesses that extend between and over the acinarand ductal lining cells. They display features of bothsmooth muscle and epithelium, such as numerous microfilamentswith focal densities in the cytoplasmicprocesses, and desmosomes that attach the myoepithelialto the epithelial cells [62]. Similarly, immunohistochemistryshows that myoepithelial cells stainstrongly with alpha smooth muscle actin (SMA), calponin,smooth muscle myosin heavy chain (SMMHC)[164], h-caldesmon [74], S-100 protein [114] as well aswith some cytokeratins (e.g. subtype 14). Maspin, p63[8, 166] and CD 10 [143, 183] have recently been describedas markers of breast myoepithelial cells, andmay have a role in identifying their salivary equivalents.Preliminary studies show that p63 may well havepractical value [166]. Scattered nests of sebaceous cellscan be seen in normal parotid and minor salivaryglands [62].Serial sectioning has shown an average of 20 lymphnodes within each parotid [67], and they may be affectedby inflammatory processes and neoplasms, bothprimary and metastatic. Their presence may hamperhistologic evaluation of parotid gland lesions [6].Fig. 5.1. Extravasation mucocele (mucous escape reaction): mucin-filledcavity lined with granulation tissue and macrophages5.1.2 Developmental DisordersAgenesis, aplasia, hypoplasia and atresia of the mainducts are all extremely rare. In contrast, intra-parotidnodal heterotopias are very common [129], and epithelialtumours may arise from them [175]. Extranodalheterotopia is rare, and can be subdivided into high(involvement of the ear, pituitary, mandible, etc.) or lowforms (lower neck, thyroid).Accessory parotid glands comprising salivary tissueseparate from the main gland, adjacent to Stenson’sduct, are found in 20% of people.5.2 Obstructive Disorders5.2.1 Mucus Escape ReactionThis forms an extravasation mucocele, which is definedas the pooling of mucus in the connective tissue in a cavitynot lined with epithelium. Most patients are under30 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) parotid0.6%, submandibular 1.2% and sublingual 1.1%. Thepathogenesis is traumatic severance of a duct, leadingto mucus pooling. It presents in the lip as a raised, oftenblue, dome shaped swelling of the mucosa, usually2–10 mm in diameter, but it is generally larger in thesublingual gland in the floor of the mouth where it isknown as a ranula. Microscopy shows a well-definedmucin-filled cavity lacking an epithelial lining, but linedwith granulation tissue and macrophages (Fig. 5.1).