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tinct and predominant "plasmacytoid" appearance of the epithelial cells of the neoplasm may be displayed [92].

No myoepithelial layer is seen. PAS and Alcian blue stains may be positive for mucoprotein secretion in the gland lumina and in the cytoplasm of the tumour cells.

Benign glandular tumours of the middle ear were not described until 1976 [26, 45]. It was soon reported that a glandular tumour of the middle ear, otherwise apparently identical to an adenoma, was Grimelius positive and on electron microscopy, showed numerous membrane-bound granules [75]. The use of immunohistochemistry from 1987, further confirmed the presence of neuroendocrine features in some of these neoplasms [108]. In an investigation of five cases of adenoma of the middle ear by light microscopic methods, immunohistochemistry and transmission electron microscopy, the glandular areas of the tumour in each patient showed bidirectional muci-nous and neuroendocrine differentiation. This was demonstrated by the presence of two cell types. Apically situated dark cells contained mucous granules; these cells were negative for neuroendocrine markers. Basally situated cells contained neuroendocrine granules; these cells were positive for neuroendocrine markers - vasoactive intestinal polypeptides or neuron-specific enolase [120].

It seems likely that there is but a single benign glandular neoplasm of the middle ear, the adenoma. Neuroendocrine as well as mucinous differentiation is frequent, perhaps universal, in these neoplasms. Contrary to what has been suggested by some authors there is no evidence that the presence of neuroendocrine differentiation reflects a more aggressive potential in adenomas, which are benign tumours.

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