Background As a consequence of the increasing application of ultrasound (US) technology, the detection of asymptomatic nonpalpable thyroid nodules has generally increased. The aim of our study was to assess if the anteroposterior and transverse diameter ratio of nonpalpable thyroid nodules (A/T) >= 1 could be a sonographic criterion for recommending fine-needle aspiration cytology (FNAC). Methods From January 2002 to January 2004, 828 consecutive solid nonpalpable thyroid nodules were evaluated by ultrasonography, colour-Doppler and FNAC in our department. Cases were selected from 2217 patients, referred to our thyroid unit for US-guided FNAC from the greater Brescia area, an endemic zone for goitre. Entry criteria included the presence at US of a solid thyroid nodule that was nonpalpable at physical examination, euthyroid condition and no previous diagnosis of thyroid malignancy. All patients with suspicious or malignant cytology underwent surgery. Results One hundred and twenty-seven nodules with inadequate cytology were excluded from the study. Thyroid malignancy was observed in 67 (9.6%) nodules. At US, cancers presented a solid hypoechoic appearance in 79.1% of cases, blurred margins in 47.8%, microcalcification in 73.1%, intranodular vascular pattern in 56.7% and A/T >= 1 in 83.6%. A hypoechoic appearance (OR 4.3), blurred margins (OR 2.6), microcalcification (OR 6.1), intranodular vascular pattern (OR 10.2) and A/T >= 1 (OR 22.4) were independent risk factors of malignancy. Conclusions A/T >= 1 in conjunction with at least one other sonographic risk factor is able to detect the majority of carcinoma and, moreover, it limits the FNAC procedures to only 15.9% of all the nodules.
