Thyroid nodules are a common medical problem, but whether fine-needle aspiration cytology (FNAC) is mandated for smaller non-palpable nodules, is controversial. To evaluate whether ultrasonographic features of thyroid nodules are associated with histological malignancy, and to identify useful criteria for clinical decision-making. Prospective observational study. From January 1991 to September 2004, 5198 patients were referred to our hospital for ultrasound evaluation of thyroid nodules. Overall, 7455 nodules (diameters from 6 to 100 mm) were examined; 2865 (38.4%) were <10 mm in diameter. All patients with suspicious or malignant cytology underwent surgery. Of the 349 nodules undergoing surgery, 284 were malignant. The prevalence of cancer was slightly higher in nodules>or=10 mm in diameter vs. those<10 mm (5.5% vs. 3.0%, p<0.01). However, histological type and local aggressiveness were largely independent of nodule size. Microcalcifications (72.2% vs. 28.7%; p<0.001; OR 6.4, 95%CI 4.9-8.4), blurred margins (52.8% vs. 18.8%; p<0.001; OR 4.8, 95%CI 3.8-6.1), solid hypoechoic appearance (80.6% vs. 52.4%; p<0.001; OR 3.8, 95%CI 2.8-5.1), size>or=10 mm (77.4% vs. 64.9%; p<0.001; OR 1.9, 95%CI 1.4-2.5) and intranodular vascular pattern type 2 (61.6% vs. 49.7%; p<0.001; OR 1.6, 95%CI 1.2-2.0) were all significantly more frequent in malignant than in benign nodules. These associations were similar when large and small nodules were analysed separately. No single parameter, including nodule size, satisfactorily identifies a subset of patients to be electively investigated by FNAC, although several may be useful in this regard.
