O. Picado Roque1, J. C. Farrá1,2, S. Liu1, W. Ouyang1, R. Teo1, A. Franco1, M. Gunder1, J. I. Lew1,2 1University Of Miami,Division Of Endocrine Surgery,Miami, FL, USA 2Sylvester Comprehensive Cancer Center,Miami, FL, USA
Introduction: With the widespread use of diagnostic imaging modalities, incidentally discovered thyroid nodules are often identified when evaluating patients for unrelated reasons. If the risk of underlying thyroid cancer in such incidental nodules is clinically significant, further evaluation and treatment becomes imperative. This study evaluates the malignancy rate of incidentally detected thyroid nodules by imaging compared to non-incidental thyroid nodules in surgical patients.
Methods: A retrospective review of prospectively collected data of 811 patients who underwent thyroidectomy at a tertiary referral center was performed. Patients who had incidentally discovered thyroid nodules by imaging studies unrelated to thyroid disease were stratified according to age, sex, FNA results, imaging modality, cytological features, and final histopathology. Malignancy rates were determined for incidentally discovered thyroid nodules. Categorical variables were compared among groups using chi-square or Fisher’s exact tests as appropriate. Student’s t-tests were used to compare continuous measures.
Results: Of 811 patients, 12.1% of patients (n=98) had incidental thyroid nodules detected by imaging, whereas 87.9% of patients (n=713) were non-incidental. Of patients with incidentally discovered thyroid nodules, 66.3% (n=65) had malignancy whereas 56.4% (n=402) of patients with non-incidental thyroid nodules had malignancy on final pathology. Overall, 14% (65/467) of patients with malignancy identified on final pathology were discovered incidentally by routine imaging. The most common imaging modality leading to detection included in descending order: non-thyroid ultrasound (n=31, 31.6%), CT (n=28, 28.6%), MRI (n=23, 23.5%), PET (n=15, 15.3%), and chest x-ray (n=1, 1%). Rates of malignancy according to imaging modality were as follows: 71% for ultrasound, 57% for CT, 61% for MRI, 86.7% for PET. Of patients with incidental thyroid nodules harboring malignancy, 52% had follicular variant papillary thyroid cancer (PTC) (n=31), 20% classical variant PTC (n=12), 14% tall cell variant PTC (n=8), and 14% diffuse sclerosing variant PTC (n=8) on final pathology. Patients with incidentally discovered malignant thyroid nodules were more likely to have lymphovascular invasion compared to non-incidental malignant thyroid nodules (53% vs. 41%, p=0.07). Extrathyroidal invasion was identified in 23% (n=15) of patients with malignant incidental thyroid nodules.
Conclusion: Incidentally discovered thyroid nodules by imaging represent an important group of surgical patients with clinically significant rates of underlying malignancy. Furthermore, a higher than expected proportion of such patients demonstrated aggressive histological features on final pathology. Patients with incidentally discovered thyroid nodules by imaging should undergo appropriate evaluation and counseling for further surgical treatment.