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Image of the Week
Edited and moderated by Stacey Mills, MD, Pathology Network's Image of the Week Blog is a forum for the discussion of interesting and often diagnostically challenging pathology images.
Friday, May 10, 2013
A 48-year-old man with decreased hearing.
A 48-year-old man had gradually progressing decreased hearing in his right ear over several months.  Routine physical examination demonstrated a conductive hearing loss.  An otoscopic exam showed an apparent mass behind the tympanic membrane and a clinical diagnosis of "glomus tumor" was made.  An excision was performed.  The small mass was adherent to the ossicles but was easily removed with minimal blood loss.  Representative sections are shown below.
The lesion consists of loosely cohesive aggregates of polygonal epithelioid cells with prominent glassy cytoplasm imparting a plasmacytoid or rhabdoid-like appearance.  The cells are relatively uniform with no evidence of mitotic activity. 
What is your diagnosis?
This is an example of a middle ear adenoma (MEA), a benign lesion of middle ear lining mucosa that can have a quite variable microscopic appearance.  In addition to the discohesive plasmacytoid cell appearance seen in this example, these tumors may form sheets, nests, trabecula, glandular structures and other adenomatous patterns.
Immunohistochemical studies will frequently demonstrate neuroendocrine differentiation in the neoplastic cells of MEA, but this feature doesn't not correlate with more aggressive clinical behavior and such tumors should not be labelled as "carcinoid tumors" or "well-differentiated neuroendocrine carcinomas."  However, in acknowledgement of this feature, the term "middle ear neuroendocrine tumor" has also been applied to these lesions.  The latter term, however, imparts no information about the malignant/benign status of the lesion, and for that reason, I prefer to label these as middle ear adenomas.
MEAs are slowly growing tumors that may have been present for many months or even years.  They are usually cured by simple excision, but they may recur.  They do not invade bone, but may tightly adhere to the middle ear ossicles and exhibit limited extension along branches of the facial nerve.  Although MEAs are often confused clinically with paraganglioma ("glomus tumor") of the middle ear, they are easily distinguished histologically and by their strong cytokeratin positivity.  At the time of surgery MEAs lack the hypervascularity and often excessive bleeding associated with the resection of a middle ear paraganglioma.  MEAs should also be distinguished from the much more aggressive papillary endolymphatic sac / temporal bone tumor that is frequently associated with von Hippel-Lindau syndrome.  MEAs lack papillary structures.
About the Author

Stacey E. Mills, MD
Stacey E. Mills, MD, a graduate of University of Virginia (UVA) and the UVA Medical Center, has authored nearly 230 articles, 20+ books, atlases and monographs—including the renowned Sternberg's Diagnostic Surgical Pathology. He has been a practicing Professor and Staff Pathologist at UVA for 30+ years and is Director of Surgical Pathology and Cytopathology. His clinical specialty is general surgical pathology with emphasis on neoplasms and neoplasm-like lesions. Dr. Mills is also Editor-in-Chief of The American Journal of Surgical Pathology.