Thyroid papillary microcarcinoma - Is it really a pitfall of fine needle aspiration cytology?

OBJECTIVE: To assess the role of fine needle aspiration (FNA) of the thyroi d in the diagnosis of papillary microcarcinoma. STUDY DESIGN: Eight cases of papillary microcarcinoma were diagnosed by fin e needle aspiration. On histologic examination they were found to be adjace nt to larger nodules of interest. The microcarcinomas were inadvertently sa mpled when sampling larger, dominant nodules. RESULTS: None of the eight dominant nodules were papillary carcinoma; seven were benign lesions, and one was an angioinvasive Hurthle cell carcinoma. In three cases tile microcarcinomas were situated within the capsule of a h yperplastic nodule. On histologic examination, five cases had multifocal mi crocarcinomas, with one case having multiple node metastases. Based on the clinical findings and morphologic features, there were no definitive cytolo gic 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 de termined until complete histologic examination reveals it to be truly incid ental and clinically insignificant.