High sensitivity and positive predictive value of fine-needle aspiration for uncommon thyroid malignancies

Fine-needle aspiration (FNA) is a screening and diagnostic tool used to triage the management of thyroid nodules. While FNA has proved to be a sensitive means of detecting common thyroid malignancies, less is known about the sensitivity and positive predictive value (PPV) of FNA for uncommon thyroid malignancies, including anaplastic thyroid carcinomas, medullary thyroid carcinomas, lymphomas, metastatic carcinomas, and other malignancies. We reviewed our experience with these uncommon malignancies sampled by thyroid FNA and recorded interpretations according to the Bethesda System. We compared the FNA interpretations to the follow-up cytology, histology, and flow cytometry. The sensitivity and PPV were as follows: anaplastic thyroid carcinoma (sensitivity 100%, PPV 89%), lymphoma (sensitivity 100%, PPV 100%), medullary thyroid carcinoma (sensitivity 83%, PPV 100%), metastatic carcinoma (sensitivity 80%, PPV 80%), and other malignancy (sensitivity 100%, PPV 100%). Four false-negative and two false-positive diagnoses were identified. While cases were nearly always triaged correctly, occasional pitfalls were encountered.