Objective: To assess the role of fine needle aspiration (FNA) of the thyroid in the diagnosis of papillary microcarcinoma.
Study design: Eight cases of papillary microcarcinoma were diagnosed by fine needle aspiration. On histologic examination they were found to be adjacent to larger nodules of interest. The microcarcinomas were inadvertently sampled when sampling the larger, dominant nodules.
Results: None of the eight dominant nodules were papillary carcinoma; seven were benign lesions, and one was an angioinvasive Hürthle cell carcinoma. In three cases the microcarcinomas were situated within the capsule of a hyperplastic nodule. On histologic examination, five cases had multifocal microcarcinomas, with one case having multiple lymph node metastases. Based on the clinical findings and morphologic features, there were no definitive cytologic findings that could distinguish between "incidental" microcarcinoma and clinically significant papillary carcinoma.
Conclusion: The detection of microcarcinoma by FNA should not be considered a false positive finding since the exact nature of the lesion cannot be determined until complete histologic evaluation reveals it to be truly incidental and clinically insignificant.