Answer: Middle ear adenoma

Histology: The tumor consists of nests and cords of eosinophilic cells with uniform round nuclei. There is focal overt glandular differentiation. Immunostains show that the tumor is diffusely positive for synaptophysin and chromogranin, and there appears to be two cell populations: luminal cells that are CK7 positive and basal cells that are CK5/6 and p63 positive. S100, actin, and calponin were negative.

Discussion: Location is important when dealing with tumors of the ear. Ceruminous gland adenomas arise from the outer ear, and endolymphatic sac tumors arise from the middle ear. Middle ear adenoma is a benign neoplasm that arises within the middle ear. It is gland forming and cytologically bland; it is not uncommon for middle ear adenoma to exhibit neuroendocrine differentiation cytologically (e.g., salt-and-pepper chromatin), architecturally (e.g., nests and trabeculae), and by immunohistochemistry (e.g., synaptohysin and chromogranin). While middle ear adenomas were once separated from middle ear carcinoid tumors, the most recent WHO classification system considers them to be the same entity. Interestingly, Lott Limbach, et al. recently demonstrated that middle ear adenomas do possess two cell populations: luminal cells that are positive for CK7 and abluminal/basal cells that are positive for CK5/6 and p63. Unlike ceruminal gland adenomas, however, S100 and actin are consistently negative indicating that true myoepithelial differentiation is not present. Middle ear adenoma is generally non-aggressive, though it may recur if incompletely excised.

Reference(s):
– Lott Limbach AA, et al. Head Neck Pathol. 2012;6(3):345-53.
– Torske KR and Thompson LD. Mod Pathol. 2002;15(5):543-55.