Definition

Cystadenoma is a rare benign epithelial tumour characterized by predominantly multicystic growth in which the epithelium demonstrates adenomatous proliferation. The epithelial lining is frequently papillary and rarely mucinous.

 ICD-O code 8440/0

 Synonyms

 Monomorphic adenoma, cystic duct adenoma {2301}, Warthin tumour without lymphoid stroma {668}, intraductal papillary hyperplasia {401}, oncocytic cystadenoma.

Epidemiology

 The frequency of cystadenoma is between 4.2-4.7% of benign tumours {668,2711}. There is a female predominance and the average age of patients with cystadenoma is about 57 years (range 12-89).

Localization

About 45% of all cases of cystadenoma arise in the parotid; the majority of tumours are located in minor salivary glands, particularly in the lips and buccal mucosa {668,2711}.

Clinical features

 Cystadenomas of the major glands typically present as slowly enlarging painless masses. In oral mucosa, these tumours produce smooth-surfaced nodules that resemble mucoceles.

 Macroscopy

Cut section reveals multiple small cystic spaces or a single large cyst surrounded by lobules of salivary gland or by connective tissue.

 Histopathology

 Cystadenomas are often well circumscribed and surrounded by complete or incomplete fibrous capsules. The tumours are composed of cystic spaces, the number and size of which is variable. Twenty percent of cystadenomas are unilocular {2711}. Most cases are multilocular with individual cystic spaces separated by limited amounts of intervening stroma. The lumens often contain eosinophilic material with scattered epithelial, inflammatory or foamy cells. Rarely, psammoma bodies or crystalloids have been described within the luminal secretion {2389}. The lining epithelium of these cystic structures is mostly columnar and cuboidal. Oncocytic, mucous, epidermoid and apocrine cells are sometimes present focally or may even predominate. An oncocytic variant of cystadenoma is composed predominantly of oncocytes in unilayered or bilayered papillary structures thus resembling the epithelium of Warthin tumour without lymphoid stroma. Cystadenomas often show a mixture of cell types in the epithelial lining. An unusual case of oncocytic cystadenoma with apocrine, mucinous, sebaceous and signet ring cell appearance has been described {1715}. Squamous epithelium may be present focally but rarely predominates. Cystadenomas of the salivary glands are usually devoid of foci of solid growth, cytologic atypia, fibrosis and apposed lymphoid tissue {790}. Cystadenoma occurs in two major variants, as papillary and mucinous cystadenoma. Papillary cystadenoma is composed of large multilocular or unilocular cysts with multiple papillary projections. The lining epithelium is, in some cases, composed of oncocytic cells. Mucinous cystadenoma is composed of multiple cysts lined by mucous tall columnar epithelium with small basally situated nuclei and eosinophilic to clear cytoplasm. The lumens contain PAS and mucicarmine positive abundant mucus. The columnar epithelial lining has a uniform thickness with limited papillary growth.

 Prognosis and predictive factors

Cystadenomas are benign tumours, and conservative but complete surgical removal is recommended. The tumours are unlikely to recur but rare cases of mucinous cystadenoma with malignant transformation have been described {1716}.