[Thyroid nodules--differential diagnosis guidelines].

Thyroid nodules are common. The vast majority of those represent hyperplastic or adenomatous nodules, true follicular adenomas, or malignant tumours. Due to the clinical relevance, the main task of the pathologist is thus to exclude or demonstrate malignancy preoperatively by fine needle aspiration (FNA) cytology, intraoperatively by frozen section diagnosis, and postoperatively by conventional histological examination. In this paper guidelines for the diagnosis and differential diagnosis of thyroid nodules are formulated. Features for the diagnosis of thyroid carcinomas include papillary structures, the characteristic cytological changes of papillary carcinoma, vascular invasion and/or capsular invasion. However, the evaluation of thyroid nodules still depends on routine cytological or histological specimens since no modern techniques are currently available to distinguish in particular benign from malignant nodules.