Answer: Middle ear adenoma

Histology: The surface is lined by low cuboidal cells pointing to the middle ear location of this neoplasm. The submucosal is involved by back-to-back glandular structures formed by a single layer of uniform cuboidal cells. Papillations are not identified, and a myoepithelial layer is not appreciated. The cells lack pleomorphism, and mitotic figures are not identified. The lumens of the ducts contain eosinophilic secretions.

Discussion: Middle ear adenomas are benign glandular neoplasms arising from the cuboidal epithelium of the middle ear. They are regarded as non-aggressive neoplasms in that they have no propensity to invade bone and invade local structures. Complete surgical removal is curative, but recurrences have rarely been reported following incomplete removal.

Middle ear adenomas often demonstrate neuroendocrine features morphologically and immunohistochemistry. The distinction between middle ear adenoma and middle ear carcinoid tumor is of no clinical relevance, and thus the dilemma of separating these two neoplasms is no longer considered to be of any practical importance. Middle ear adenomas consistently demonstrate a proliferation of back-to-back glands; and they lack the solid nests and highly vascularized stroma of paraganglioma. Rarely, a ceruminal gland adenoma of the outer ear will secondarily involve the middle ear by direct extension. These ceruminal gland adenomas are identified by the presence of a double cell layer: an inner secretory layer of apocrine-like secretory cells, and an outer layer of myoepithelial cells. The middle ear can also by secondarily involved by an endolymphatic sac tumor of the inner ear. The endolymphatic tumor is much more aggressive than a middle ear adenoma, and is characterized by infiltration of bone. Although both tumors may exhibit a glandular proliferation of cytologically bland cells, the endolymphatic sac tumor consistently demonstrates a papillary component. This is an important differentiating feature as middle ear adenomas do not demonstrate papillary growth.