Significance of ultrasound features in predicting malignant solid thyroid nodules: need for fine-needle aspiration.

OBJECTIVE: The purpose of this study was to provide sonographic and colour flow criteria helpful for differentiation between benign and malignant solid thyroid nodules.

METHODS: This prospective study was carried out at Sindh Institute of Urology and Transplantation (SIUT), Karachi Pakistan from 01.05.07 to 31.12.08. Sonographic scans of 78 thyroid nodules in 66 patients were performed and characteristics of thyroid nodules that were studied included microcalcifications, an irregular or microlobulated margins, marked hypoechogenicity, a shape that was taller than it was wide and color flow pattern in Color Doppler ultrasound. The presence and absence of characteristics of nodules were classified as having positive or negative findings. If even one of these sonographic features was present, the nodule was classified as positive (malignant). If a nodule had none of the features described, it was classified as negative (benign). The final diagnosis of a lesion as benign (n = 53) or malignant (n = 25) was confirmed by fine needle aspiration biopsy, and patients who were proved to have benign lesions were followed-up for 6 months and malignant lesions which were proved on histopathology after FNA were subjected to surgery. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were then calculated on the basis of our proposed classification method.

RESULTS: Among 78 solid thyroid nodules 35 lesions were classified as positive considering the sonographic characteristics and 23 of them were proved to be malignant on histopatology. Out of 43 lesions which were classified as negative, 2 were proved to be malignant. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy based on our sonographic classification method were 93.8%, 66%, 56.1%, 95.9%, and 74.8%, respectively.

CONCLUSION: Ultrasound is valuable for identifying many malignant or potentially malignant thyroid nodules. No single ultrasound criterion is reliable in differentiating all benign from malignant thyroid nodules, but many US features aid in predicting the benign or malignant nature of a given nodule. Fine-needle aspiration biopsy should be performed on thyroid nodules classified as positive, regardless of palpability.