Abstract
Recently, Kim et al. (1) reported a small series of 27 solid, isoechoic thyroid nodules ≥5 mm which exhibited no suspicious ultrasound (US) features (i.e., they were round, regular nodules without calcification). Basically, two results were obtained. First, analysis of the vascularization pattern did not contribute to the identification of malignant nodules. In fact, the value of Doppler imaging in nodular thyroid disease continues to be highly controversial. The most surprising result was the high rate of malignancy of these nodules (27%), which are traditionally regarded as low risk for carcinoma. We previously reported a rate of malignancy of only 1.5% for solid, iso- or hyperechoic nodules without suspicious US features (2). This value agrees with the rate of ≤3% reported by other investigators (3 –5).
In order to understand the significance of the result reported by Kim et al. (1), it seems to be important to know the rate of malignancy of solid hypoechoic and/or suspicious nodules (considering calcification, margins, and shape). If the frequency of carcinomas were similar for iso- and hypoechoic nodules, the conclusion would be that echogenicity is of no diagnostic value for solid nodules. Likewise, if malignancy were similar for nodules with and without suspicious findings, the conclusion would be that these findings have no predictive value for malignancy. Or even, if no difference in the occurrence of cancer were detected between unsuspicious isoechoic (1) and suspicious hypoechoic nodules, the conclusion would be that no US feature is useful for the definition of the nature of solid nodules. Conversely, if the frequency of malignancy was higher in the case of hypoechoic or suspicious nodules (e.g., >50%), this would confirm the usefulness of this imaging method. At the same time, it would support the hypothesis that the population studied by Kim et al. (1) was somehow at very high risk of thyroid malignancy and the results cannot be extrapolated to patients with nodules in general whose risk of developing carcinoma is only 5–10%.
This isolated result (rate of malignancy for unsuspicious solid isoechoic nodules) does not permit any conclusion to be drawn concerning the usefulness of echogenicity in solid nodules and the value of other US findings (calcification, margins, and shape). It does, however, suggest that the population studied was at very high risk for malignancy.