[Thyroid nodule. Differential diagnostic guidelines]

Nodules in the thyroid are common. They may represent hyperplastic or adenomatous nodules, true adenomas or malignant neoplasms. The main task of the pathologist consists of the exclusion or demonstration of malignancy. This can be done preoperatively by fine needle aspiration (FNA) cytology, intraoperatively by frozen section diagnosis, and postoperatively by investigation of paraffin sections. The intention of this paper is to formulate guidelines for the diagnosis and differential diagnosis of thyroid nodules. The evaluation of thyroid nodules still depends on routine cytological or histological specimens since immunohistochemistry, flow-cytometry and molecular biological techniques sofar failed to provide significant aid in the process of distinguishing benign from malignant thyroid nodules.