Fig. 5.4. Simple, benign lymphoepithelial cyst. The cavity is lined with columnar and cuboidal cells with scattered goblet cells. The surrounding tissue contains small lymphocytes and macrophages. Beyond this is a capsule and subcapsular space resembling that of a lymph node

Fig. 5.5. Sclerosing polycystic adenosis. Cystic ducts of varying size with stromal fibrosis, resembling fibrocystic disease and sclerosis adenosis of the breast. There is also proliferation of ducts and acini in a lobular pattern Benign Lymphoepithelial Cyst

Benign lymphoepithelial cysts are thought to arise either in intraparotid lymph nodes [60] or from remnants of the branchial apparatus [10]. There is no clinical association with Sjögrens syndrome, and they were described long before the AIDS epidemic. There is a slight male preponderance (1.6:1 in civilians in the Armed Forces Institute of Pathology [AFIP] series), and the mean age of onset is 46 years (range 18 to 79) [113]. They are usually solitary, but can occasionally be bilateral. The average diameter is 25 mm, but they may reach 70 mm. Microscopy shows the lining epithelium to be squamous, respiratory, cuboidal, columnar or a combination, and small numbers of goblet cells may also be present (Fig. 5.4). This lining is surrounded by abundant lymphoid tissue composed of small lymphocytes, plasma cells and germinal centres; lympho-epithelial lesions are not a feature. Benign lymphoepithe-lial cysts are not known to recur after surgical excision.

A nodular or diffuse enlargement of particularly the parotid glands is often seen in HIV-positive patients - usually bilaterally. Microscopic examination shows a dense lymphoid infiltrate including follicular hyperplasia, sometimes displaying lysis of germinal centres and diminished mantle zones. There is an elaborate dendritic reticulum cell network within which there is evidence of active HIV replication, although the exact histogenesis of this lesion is not understood. Plasma cells (polytypic) are often numerous. The glandular parenchyma is atrophic, and multiple cystic spaces are seen, filled with mucoid or gelatinous fluid. The cysts are dilated ducts, and the lining sometimes shows squamous metaplasia. The cysts are infiltrated by lymphoid cells, including variable numbers of marginal zone B-cells, and in time lymphoepithelial lesions are apparent.

There is considerable morphological overlap with LESA [60, 91], but only a minority of patients exhibit the clinical features of Sjogren's syndrome [105]. An important practical point is that this lesion can be the first clinical manifestation of HIV disease, and thus histological identification of it means a diagnosis of AIDS for the patient.

The lymphoid infiltrate is polyclonal and generally does not progress to lymphoma, although patients with HIV disease are at risk of developing aggressive B-cell lymphomas, most commonly of the Burkitt-type and diffuse large cell lymphoma [107]. An exception is that in children with AIDS, the infiltrate more closely resembles MALT lymphoma, and monoclonality may be demonstrated.

5.7.5 Sclerosing Polycystic Sialadenopathy

(Sclerosing Polycystic Adenosis)

This is a benign pseudoneoplastic condition of major salivary glands [11, 84, 200], said to be analogous to fibrocystic disease of the breast [58]. It affects mainly females with a mean age of 28 years (range 12 to 63). Most cases have been described as slow-growing masses in the parotid gland, with a single example of submandibular gland involvement. The excised gland is largely replaced Cystic Lymphoid

Hyperplasia of AIDS

by multiple discrete, firm, rubbery nodules. Microscopic examination shows a well-circumscribed, unencapsu-lated mass composed of a lobular arrangement of proliferating ducts and acini with cystic ducts containing viscous secretion and, on occasions, aggregates of foamy macrophages. There is often intraluminal epithelial proliferation occasionally with a cribriform pattern and these may contain small droplets of basement membrane material. The lining comprises a spectrum of apocrine, mucous, squamous cells and ballooned sebaceous-like cells, although true goblet cells are not seen. Some cells contain prominent large, intensely eosinophilic cytoplasmic granules of varying sizes, representing aberrant zymogen granules (Fig. 5.5). On occasion there is nuclear pleomorphism, even suggesting dysplasia [200], but there is no significant mitotic activity and no malignant cases have been described. Flattened myoepithelial cells are present around ductal and acinar structures, and there is periductal sclerosis and intense hyaline sclerosis of the surrounding soft tissue. Sometimes, a patchy lymphocytic infiltrate is noted. About one-third of cases recur, but none has metastasised.

5.7.6 Other Cysts

Other salivary cysts include dermoids [141], and a variety of epithelial and non-epithelial cysts including parasites and gas cysts in glass blowers [163]. Keratocystoma is a rare, recently described, benign parotid tumour characterised by multicystic keratin-filled spaces lined with stratified squamous epithelium with no atypical features [150].

5.8 Benign Tumours

There are various classifications. The revised WHO classification (Table 5.1) [171] has the merit of being easily applicable in practice [181].

5.8.1 Pleomorphic Adenoma


Most authors accept that there is a spectrum of benign salivary adenomas, including pleomorphic adenoma. Benign myoepithelioma, which is composed almost entirely of myoepithelial cells represents one end of the spectrum, whereas basal cell adenoma and canalicular adenoma are at the other end [183, 236, 237]. The particular morphology of any particular tumour reflects the different proportions of the constituent cells (Fig. 5.6).

Pleomorphic adenoma (PA) is the most common tumour of the salivary glands. Although most often found in young to middle-aged women, they can occur in ei-

Fig. 5.6. Pleomorphic adenoma spectrum. Reproduced with permission from Zarbo et al. [236]

ther sex and at any age. Up to 80% occur in the superficial lobe of the parotid gland, and it typically presents as a painless swelling. When the deep lobe is involved, it often manifests as an intraoral parapharyngeal mass. Approximately 5% of PAs occur in the submandibular gland, 0.1% in the sublingual gland and about 10% in minor salivary glands [30, 228]. Similar tumours arise in extrasalivary locations including bronchi, ear, lacrimal gland, breast and skin.

Macroscopically, PAs are usually well-circumscribed masses of 20-40 mm. The cut surface is usually white, and grey glistening areas are commonly seen.

Histologically, PA was defined by the revised WHO Classification of 1991 as "a tumour [of the salivary glands] of variable capsulation characterised microscopically by architectural rather than cellular pleomorphism" [171], i.e. the pleomorphism refers to the variety of histological patterns, not the cytology.

The pattern varies from case to case, and also from area to area within any individual tumour. All are composed of a mixture of ductal epithelial cells, basal and myoepithelial cells and variable amounts of stroma, both hyaline and chondromyxoid. Attempts have been made to subclassify PA based on the proportions of cell types and stroma [176], but because of the variation in any tumour, this is difficult and probably has no prognostic value.

Ducts are lined with flat, cuboidal or columnar epithelial cells, with little or no atypia. The ducts are usually small tubules, but can be cystically dilated and also arranged in a cribriform pattern, resembling adenoid cystic carcinoma, but mitotic figures are rare and the proliferation index low (see Sect. 5.9.3). Squamous metaplasia with or without keratinisation is seen in up to 25% of PAs [65]. If associated with mucinous metaplasia, it may resemble mucoepidermoid carcinoma (Figs. 5.7, 5.8).

Myoepithelial cells are arranged in sheets, smaller islands and trabeculae, and also surround epithe-

Table 5.1. Revised WHO histological classification of salivary gland tumours [171]

Adenoma s

Ductal papilloma

Cystadenoma Carcinomas

Non-epithelial tumours

Malignant lymphomas

Secondary tumours

Unclassified tumours

Entities not included in the classification, but described or better characterised since

Pleomorphic adenoma

Myoepithelioma (myoepithelial adenoma)

Basal cell adenoma

Warthin's tumour (adenolymphoma)

Oncocytoma (oncocytic adenoma)

Canalicular adenoma

Sebaceous adenoma

Inverted ductal papilloma

Intraductal papilloma

Sialadenoma papilliferum

Papillary cystadenoma

Mucinous cystadenoma

Acinic cell carcinoma

Mucoepidermoid carcinoma

Adenoid cystic carcinoma

Polymorphous low-grade adenocarcinoma (terminal duct adenocarcinoma)

Epithelial-myoepithelial carcinoma

Basal cell adenocarcinoma

Sebaceous carcinoma

Papillary cystadenocarcinoma

Mucinous adenocarcinoma

Oncocytic carcinoma

Salivary duct carcinoma

Adenocarcinoma (not otherwise specified)

Malignant myoepithelioma (myoepithelial carcinoma)

Carcinoma in pleomorphic adenoma

Squamous cell carcinoma

Small cell carcinoma

Undifferentiated carcinoma

Other carcinomas


Hyalinising clear cell carcinoma Cribriform adenocarcinoma of the tongue Endodermal sinus tumour of the salivary glands lium-lined spaces. As in benign myoepithelioma (see Sect. 5.8.2), neoplastic myoepithelial cells may take several forms - epithelioid, spindle, plasmacytoid, clear and oncocytic, as well as transitional forms with features of two or more of these types (Fig. 5.9).

The stroma varies in amount and is either dense eo-sinophilic hyaline material or chondromyxoid tissue. The former is composed of basement membrane material and stains with PAS diastase and collagen type IV; the chondromyxoid material only rarely resembles true cartilage and is Alcian blue-positive (Fig. 5.10). Calcification and bone formation can occur in long standing tumours. Occasionally, collagenous spherules and crys talloids are seen, particularly in tumours rich in myoepithelial cells of the plasmacytoid type (Fig. 5.11) [197]. Nuclear atypia is not common, but can be seen in tumours where epithelial or myoepithelial cells display oncocytic features [65]. Occasional myoepithelial cell nuclei are enlarged and bizarre, somewhat analogous to "ancient" change in schwannomas. Mitotic figures are generally sparse, but can occur as part of the repair process after FNA. Such tumours with these atypical features should be sampled thoroughly to exclude true in-tracapsular carcinoma.

Similarly, areas of necrosis or haemorrhage may follow surgical manipulation, FNA or other trauma, and

Fig. 5.7. Pleomorphic adenoma: myoepithelial cells with an epithelioid cytomorphology. These cells may also be spindle-shaped, plasmacytoid (hyaline) or have clear cytoplasm. Note also a small duct and a focus of squamous metaplasia. Keratinising squamous metaplasia is seen in up to a quarter of pleomorphic adenomas

Fig. 5.7. Pleomorphic adenoma: myoepithelial cells with an epithelioid cytomorphology. These cells may also be spindle-shaped, plasmacytoid (hyaline) or have clear cytoplasm. Note also a small duct and a focus of squamous metaplasia. Keratinising squamous metaplasia is seen in up to a quarter of pleomorphic adenomas

Fig. 5.8. Pleomorphic adenoma with squamous and focal muci-nous metaplasia resembling mucoepidermoid carcinoma
Fig. 5.9. Pleomorphic adenoma: myoepithelial cells showing an epithelioid and plasmocytoid appearance
Fig. 5.10. Pleomorphic adenoma: chondromyxoid stroma containing isolated small and small aggregates of myoepithelial cells
Fig. 5.11. Collagenous spherules can be seen in some benign myo-epitheliomas and myoepithelium-rich pleomorphic adenomas
Fig. 5.12. Vascular "invasion" is a rare finding in benign pleo-morphic adenoma, due to displacement of neoplastic cells into vascular spaces. It is not indicative of malignancy
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