Pitfalls in the diagnosis of thyroid neoplasms

To the casual observer, the neoplastic pathology of the thyroid gland appears relatively simple. There are only two major epithelial cell types to deal with, and these produce less than a handful of tumor types, most of which are defined by seemingly strict and easily followed criteria. Yet, behind this apparent simplicity there is a world of complexities. Each rule has its exception, each criterion is of only relative value, and each morphologic feature needs to be evaluated in the context of the entire picture. As a result, pitfalls abound, as any experienced pathologist knows too well. The list which follows enumerates those that we have encountered more frequently in our practice. Included in this review are not only morphologic but also conceptual pitfalls, the latter being probably responsible for more diagnostic errors than the former.