A 54-year-old woman underwent a superficial parotidectomy for a mass lesion that was interpreted as a typical mixed tumor ("pleomorphic" adenoma). This lesion is not illustrated. In the surrounding parotid gland the incidental lesion shown below was noted.
What is your diagnosis?
The photomicrographs show a loose aggregate of ducts lined by cytologically uniform cells with a low-columnar to cuboidal appearance. The ducts have the histologic appearance of normal intercalated ducts and this finding has been referred to as intercalated duct hyperplasia. Larger forms of this process, often with a peripheral capsule, have been referred to as intercalated duct adenomas, though the distinction between the two is often arbitrary and hybrid forms clearly exist.
These small, incidental proliferations can be seen in adjacent normal salivary (usually parotid) tissue removed for other reasons, though it was not until relatively recently that they were well-documented in the literatue in an article by Weinreb and colleagues in 2009 (Am J Surg Pathol 2009;33:1322-9). The authors note that although these small lesions can occasionally be found in salivary tissue removed for any reason, there appears to be an association with basal cell adenomas and epithelial-myoepithelial carcinomas, suggesting that the intercalated duct lesions could be precursors for other more important forms of salivary neoplasia.
Further studies will be necessary to more firmly establish an association with clinically significant neoplasia. In the mean time, keep an eye out for these nodules in salivary tissue adjacent to a more obvious tumor, and I bet you'll find them. And now you know what to call them!