The diagnostic limit of fine-needle aspiration cytology (FNAC) in the evaluation of thyroid follicular lesions.

Fine-needle aspiration cytology (FNAC) represents the most important diagnostic tool for the preoperative diagnosis of thyroid carcinomas. However, although FNAC is very reliable in assessing the presence of medullary, papillary and anaplastic thyroid carcinomas, its diagnostic value decreases for the follicular lesions due the limited distinction between malignant and benign tumors. In the present study, we reviewed 39 cases, out of 721 FNAC based diagnosis performed at the Thyroid Clinic of Policlinico “Umberto I” of Rome over a 2 years period, with a FNAC diagnosis of follicular lesion that warranted thyroidectomy and compared the cytological features with the histological diagnosis. All FNAC samples were analysed by one cytopathologist and the final diagnosis was reported by two different histopathologists. Of the 39 cases reviewed, solitary and multinodular goiters were present in 11 (29%) and 28 (71%) of patients, respectively. The ultrasound evaluation of the nodules showed that the greatest diameter ranged from 8 to 45 mm and that 30 (77%) were hypoechoic, 7 (18%) were isoechoic a 2 (5%) were mixed. The histologic follow-up was available for 21 patients and showed 18 cases (85.7%) of benign lesions, comprising 13 cases of nodular hyperplasia, 2 cases of autoimmune thyroidites and 3 cases of follicular adenoma, while the remaining 3 cases (14.3%) were 2 Hürthle cell carcinomas and 1 papillary carcinoma. Even if the number of patients analysed in this study is limited, no correlation appears to be between malignancy and sex, echogenicity, nodular size, presence of microcalcification, multinodularity or color flow-doppler patterns. On the contrary, age may represents a major risk factor as all 3 carcinomas were observed in patients over 60 years of age. In conclusion, our data indicate that more of 85% of nodules with a FNAC based diagnosis of follicular lesion that warranted thyroidectomy showed to be benign tumors of the thyroid on histological evaluation and that age over 60 years may represent a risk factor for malignancy.