Thyroid lesions visualized on CT: sonographic and pathologic correlation

There are no definitive guidelines for the management of incidental thyroid lesions on computed tomography (CT). The objectives of our study were to assess the association between CT and ultrasound (US) characteristics of thyroid lesions and identify CT predictors of benignity or malignancy.

Two hundred fifty-nine patients who had undergone both CT of the chest or neck and thyroid US had at least one thyroid lesion visible on CT; both incidentally detected and palpable or symptomatic lesions were included. The CT and US examinations were retrospectively reviewed and lesions characterized. Pathologic results from fine-needle aspiration (FNA) and surgical excision were used to classify lesions as benign or malignant. Thyroid lesions without pathologic correlation were classified as either benign or indeterminate based on US evaluation. Lesions that were cystic, predominantly cystic, solid and cystic with features consistent with a colloid nodule, or stable for at least 1 year were considered benign. Fisher exact tests, Spearman correlations, and logistic regression models were used to evaluate the associations between CT and US characteristics and CT predictors of benignity or malignancy. Multivariable logistic regression analyses were performed to examine the joint associations between the CT features and sonographically assessed benignity.

Of 259 patients, 168 (64.9%) patients had incidentally detected thyroid lesions, 49 (18.9%) patients had palpable/symptomatic lesions, and 116 (44.8%) patients underwent surgical resection and/or FNA biopsy. The malignancy prevalence was 1.8% (3 of 168) for incidental thyroid lesions and 10.2% (5 of 49) for palpable/symptomatic lesions. The malignancy prevalence of incidental lesions initially detected on CT was 1.6% (2 of 125). Of the 143 patients without pathologic data, 58 (40.6%) were classified as benign and 85 (59.4%) were categorized as indeterminate based on US evaluation. Statistically significant associations were found between CT and US with regard to lesion number, dominant lesion size, lesion consistency/composition, and associated calcifications. No CT characteristics of thyroid lesions predicted malignancy. However, there were statistically significant associations on multivariate analysis between indeterminate/benign nodules and CT characteristics of smaller lesion size, lower mean attenuation, and homogeneous composition.

Recommending sonographic evaluation of all incidentally detected thyroid lesions is likely not the appropriate strategy, given the high prevalence of thyroid incidentalomas, low probability of malignancy, and cost effectiveness of workup. Small, homogeneous, low-attenuation lesions have a high probability of being benign.