Middle-ear adenoma (MEA): a report of two cases, one with predominant "plasmacytoid' features.

Middle-ear adenomas (MEAs) are rare neoplasms which can display several histological patterns and represent a diagnostic challenge. We present two cases of MEA which share some histopathological features such as medium to small cells forming solid infiltrating tumour nests as well as scattered glandular structures with Alcian blue and PAS positive material within. The second case also displayed a distinct and predominant "plasmacytoid' appearance which, in a small biopsy, might have been misleading. Both cases expressed an admixture of epithelial and neuroendocrine immunohistochemical markers, whereas ultrastructural study demonstrated electron dense granules. Taken together, these observations support a mixed epithelial and neuroendocrine nature for these neoplasms, the differential diagnosis of which includes paragangliomas and other tumours or tumour-like lesions involving less frequently the middle ear, such as meningiomas, plasmacytomas and inflammatory polyps. The existence of MEAs with plasmacytoid features should be remembered to avoid confusion with plasmacytomas, plasmacytoid myoepithelioma and plasma cell inflammatory infiltrates.