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- rarely more than 20 mm in diameter. It has a characteristic morphology of branching and interconnecting bi-layered strands of darkly staining epithelial cells set in a loose vascular stroma (Fig. 5.20). There is no pleomorphism or significant mitotic activity. The cells express cytokeratins and S-100 protein. Not infrequently, they are multifocal [39], and can thus mimic the true invasiveness of cribriform adenoid cystic carcinoma. The lack of destructiveness and the presence of blood vessels in the cribriform spaces are good guides to canalicular adenoma, which is completely benign. Occasional recurrences are a result of multifocality [90].

5.8.7 Sebaceous Adenoma

S.S.S Sebaceous Lymphadenoma

5.8.9 Ductal Papilloma

S.S.10 Cystadenoma

ICD-O:8440/0

The revised WHO classification recognises two histo-pathological subtypes -papillary cystadenoma (similar to lymphoid-poor Warthin's tumour) and muci-

Fig. 5.21. Oncocytic (papillary) cystadenoma of the larynx. Cys-tically dilated ducts are lined with oncocytic cells

ICD-O:8410/0

This rare, encapsulated epithelial tumour is composed of solid, variably shaped islands and cysts, both showing focal sebaceous differentiation with squamous areas; these are surrounded by a fibrous, hyalinised stroma. They do not recur after complete surgical excision [12, 62].

ICD-O:8410/0

This lesion comprises irregular proliferating nests and islands of epithelium including solid and gland-like sebaceous elements, surrounded by a lymphoid stroma. It is possible that, like Warthin's tumour, sebaceous lymphadenoma develops from salivary inclusions within lymph nodes, and shows sebaceous rather than oncocytic metaplasia [62, 171].

Fig. 5.21. Oncocytic (papillary) cystadenoma of the larynx. Cys-tically dilated ducts are lined with oncocytic cells nous cystadenoma. Both are rare, benign tumours characterised by unicystic or multicystic growth patterns. The latter can be mistaken for mucinous malignancy, such as grade I mucoepidermoid carcinoma [62, 173]. Most cystadenomas are multilocular with individual cystic spaces separated by limited amounts of intervening stroma [229]. The lumina often contain eosinophilic material with scattered epithelial, foamy or inflammatory cells. Rarely, psammoma bodies and crystalloids have been described within the luminal secretion [199]. The lining epithelium of the cystic spaces is mostly columnar and cuboidal. Oncocytic, mucous and apocrine cells are sometimes present fo-cally or may predominate. An oncocytic variant of papillary cystadenoma is composed of oncocytes present in unilayered or bilayered papillary structures (Fig. 5.21). Squamous epithelium may be present, but rarely predominates. The tumours are unlikely to recur, but rare cases of mucinous cystadenoma with malignant transformation have been described (Figs 5.22, 5.23) [135].

ICD-O:8503/0

There are three subtypes, all rare - inverted ductal pap-illoma (similar to the sinonasal tumour), intraductal papilloma and sialadenoma papilliferum (similar to skin syringocystadenoma papilliferum) [62]. Intraduct-al papilloma has a fibrovascular core lined with myoepi-thelial and ductal cells and it is usually seen in a dilated duct.

5.9 Malignant Epithelial Tumours

5.9.1 Acinic Cell Carcinoma

ICD-0:8550/3

Acinic cell carcinoma (AcCC) is defined as a malignant epithelial neoplasm in which some of the neoplastic cells demonstrate serous acinar cell differentiation.

It accounts for about 2-4% of salivary gland tumours, and 12-17% of malignancies [62]. It is slightly commoner in women and the mean age at presentation is 44 years, although AcCCs can affect children

Fig. 5.22. Mucinous cystadenoma. Cysts are lined with mucus- Fig. 5.24. Acinic cell carcinoma solid variant. The cells show secreting cells without atypia granular cytoplasm and acinar differentiation similar to normal salivary gland acini

Fig. 5.22. Mucinous cystadenoma. Cysts are lined with mucus- Fig. 5.24. Acinic cell carcinoma solid variant. The cells show secreting cells without atypia granular cytoplasm and acinar differentiation similar to normal salivary gland acini

Fig. 5.23. Mucinous cystadenoma with malignant transformation [136]. Cellular pleomorphism and signet ring cell appearance
Fig. 5.25. Acinic cell carcinoma, papillary subtype: papillae are lined with intercalated duct-like cells, some containing microvesi-cles, others showing a hobnail/clear cell appearance

and centenarians. The parotid is involved in 92% of cases (3% bilateral), with only occasional examples in the submandibular or minor glands [62], or periparot-id lymph nodes [161]. The typical clinical history is of a slowly enlarging mass (for as long as 40 years) sometimes with pain and facial nerve weakness. Most tumours are partly circumscribed, with a diameter of 1030 mm, although some may reach 220 mm [4]. Microscopy shows one or more growth patterns - solid, mi-crocystic, follicular and papillary-cystic. The follicular pattern resembles thyroid tissue, and any tumour in the parotid with a papillary-cystic architecture should be considered to be an AcCC, until proven otherwise. The cells in AcCC may take one of several forms - aci-nar (serous or blue dot), intercalated ductal (cuboidal, often lining small ducts), microvesicular, hob-nail or clear - the last is surprisingly rare, being seen in only

6% of cases [62]. Several growth patterns and cell types may be seen in any individual tumour (Figs 5.24-5.26). Dedifferentiation towards a high-grade malignancy occurs occasionally [51], and all surgical specimens of AcCC must be sampled adequately. A lymphoid infiltrate is found in about 30% of cases, but is only of clinical significance (having a good prognosis) when the tumour is a well-circumscribed nodule with a microfollicular architecture (Fig. 5.27) [133].

The most useful special stain in AcCC is PASD, which highlights cytoplasmic zymogen granules (Fig. 5.28). Immunohistochemistry is of limited value - positivity is seen with cytokeratin, amylase, CEA and in 10% S-100 protein [221]. Other myoepithelial markers are negative. It has been suggested that bone morphogenetic protein-6 (BMP-6) may be useful, but this marker is not yet widely available [92]. Electron

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