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This morphological and immunohistochemical study demonstrates that tumors currently known as "middle ear adenomas" are truly well-differentiated epithelial neuroendocrine tumors (NETs) composed of cells comparable to normal intestinal L cells, and therefore, these tumors resemble hindgut NETs. These tumors show consistent expression of glucagon, pancreatic polypeptide, PYY, and the transcription factor SATB2, as well as generic neuroendocrine markers and keratins. The same L cell markers are expressed by cells within the normal middle ear epithelium. These markers define a valuable immunohistochemical profile that can be used for differential diagnosis of middle ear neoplasms, particularly in distinguishing epithelial NETs from paragangliomas. The discovery of neuroendocrine cells expressing the same markers in non-neoplastic middle ear mucosa opens new areas of investigation into the physiology of the normal middle ear and the pathophysiology of middle ear disorders.

Endolymphatic sac tumour (ELST) is a rare low grade malignant epithelial tumour of the petrous temporal bone, thought to arise from papillary epithelium of the endolymphatic sac. They may occur sporadically or in association with Von-Hippel Lindau disease. ELST is extremely rare neoplasm with benign histopathological appearance and clinically destructive behaviour. Because of the rarity of this tumour, it can easily be confused with other tumours such as paraganglioma, middle ear adenoma, metastatic carcinomas or choroid plexus papilloma. We report here a rare case of ELST with review of literature and discuss the differentiating features of ELST from its mimickers, showing a papillary configuration.

Neuroendocrine neoplasms of the ear are uncommon primary tumors. There is a reported debate in the literature as to the true nature of these tumors and how to classify them. However, there is a kind of consensus that they can represent a spectrum of a common entity with dual glandular and neuroendocrine differentiation. The differential diagnosis of these tumors is broad but their morphologic, immunohistochemical, and radiographic features help to differentiate them from other entities. The tumors have mostly bland histology and indolent biological behavior, yet they may recur and metastasize. It is important to accurately recognize these tumors in order to perform the right management and limit their morbidity. In this article, we review the pathogenesis, histology, immunohistochemical features of neurornedocrine neoplasms of the ear and we discuss their differential diagnosis, clinical behavior and management.

Adenomas of the middle ear are rare benign glandular neoplasms arising from the middle ear mucosa. After previous operations 25 and 15 years before, a 67-year-old female complained about dizziness, tinnitus, and unilateral hearing loss on the left side. A tumor in the tympanum that was revealed by otoscopy could be removed completely. Histological examinations showed an adenoma of the middle ear with cholesteatoma. This was inconsistent with the histological result of the operation in 1983, which had described a hidradenoma. An exact analysis of the preparations confirmed that a middle ear adenoma had already been present in 1983. Hidradenoma is one of the most important differential diagnoses. The characteristic histological sign of middle ear adenomas in contrast to hidradenomas is the lack of myoepithelial cells. In addition, it is very difficult to differentiate middle ear adenoma and adenocarcinoma using histopathological and clinical methods. Therefore, thorough follow-up is mandatory for patients after surgical treatment of middle ear adenomas.