Endocrine Abstracts

Fine needle aspiration (FNA) of thyroid can be confidently enlisted as a primary diagnostic tool in evaluating thyroid nodules to spot cancer, although this confidence should be tempered with awareness of possible diagnostic pitfalls. The sources of pitfalls (toward false positive or false negative results) may lie in sampling, in microscopic interpretation, or even in the clinical evaluation. Nonthyroidal lesions (parathyroid, lymph nodes, and salivary glands) aspirated ‘by mistake’ as thyroid nodules may lead to false diagnoses. Parathyroidal adenomas are mostly misdiagnosed as thyroid neoplasms. Sampling in the peritumoral tissue with thyroiditis may miss the neoplasm and lead to a false negative diagnosis. Hashimoto’s disease is a major source for false positive diagnoses based on the sometimes severe reactive epithelial atypia or on the extensive oncocytic metaplasia mimicking oncocytic neoplasm or papillary Ca (PTC). Conversely, neoplastic cells can be obscured by dense lymphoplasmocytic infiltrates. Metaplastic oxyphilic cells in hyperplastic nodules can also be overdiagnosed as neoplastic ones, whereas oxyphilic cells of PTC are sometimes interpreted as metaplastic. False negative diagnoses of PTC are sometimes due to the cystic degeneration of the neoplasm and the absence of well preserved neoplastic cells in the smears. Degenerative cell changes may be confusing. The neoplastic nature of highly differentiated PTCs, eventually of the macrofollicular, colloid rich variant, may be overlooked. Since the cells of medullary Ca may be small with minor atypia, the neoplasm may be underdiagnosed, especially in a colloid rich background due to admixtures. Sometimes the neoplasm is diagnosed as a lymphoma or a follicular lesion if the specific features are overlooked. A monomorphous pattern of small cells of a poorly differentiated Ca can also be misleading. Paucicellular anaplastic Ca may be missed. Finally, needle tract effects on repeat FNA comprise alterations like reactive follicular or endothelial cells, leading to false positive results.