Introduction Thyroid incidentalomas (TI) are incidental thyroid nodules commonly identified on non-thyroid dedicated imaging studies. While most TI are benign, approximately 10% are malignant similar to that among thyroid masses identified by other means. US guidelines recommend evaluation of all TI to risk-stratify for thyroid cancer. This practice has resulted in part to a dramatic rise in thyroid cancer incidence, yet mortality has not changed, a hallmark of overdiagnosis. With increasing utilization of medical imaging, such as chest CT for lung cancer screening, detection and evaluation of TI identified on chest CT is contributing to overdiagnosis of thyroid cancer. We examined reporting of TI on chest CT and how reporting approach affects subsequent evaluation and long-term outcomes.
Methods Retrospective cohort of 1650 US veterans with incidental thyroid nodules on chest CT. Index date was defined as date of the chest CT that reported the TI. Reporting of the TI on CT radiology report was categorized as in body of the report alone or in report ‘impression section.’ Follow-up including endocrinology consult, thyroid ultrasound, nodule fine needle aspiration (FNA), surgery, thyroid cancer diagnosis, death from thyroid cancer and all-cause mortality extracted from administrative data. Incidentaloma evaluation defined as a composite of dedicated thyroid ultrasound, endocrinology consult for nodules, or nodule fine needle aspiration.
Results 1460 subjects were included in the final analytical cohort. Mean age was 70.4 years; 1386 (94.9%) were male. 707 (48.4%) subjects had TI reported in impression section of the report and 753 (51.6%) had TI reported in body of report only. Mean age and sex did not differ by reporting location (P > 0.32). Subjects with TI reported in impression vs. body location of report were more likely to be evaluated within 6 months (35.5% vs 5.1%; P = <0.001), 12 months (38.5% vs 6.5%; P = <0.001), and at any time during the entire follow-up period (47.8% vs 13.2%; P = <0.001). Subjects with TI reported in impression vs. body location of report were more likely to undergo thyroidectomy (2.6% vs 0.8%; P = 0.009), but there was no difference in the proportion of subjects diagnosed with thyroid cancer (1.6% vs 0.8%; P = 0.18), thyroid-cancer related mortality (0.6% vs 0.1%; P = 0.16), or all-cause mortality (63.2% vs 66.5%; P = 0.19).
Conclusions Thyroid incidentalomas on chest CT are inconsistently reported and often receive no further evaluation. However, the location of reporting of TI in the radiology report is associated with the likelihood of clinical evaluation with thyroid ultrasound, endocrinology consult, and FNA. Despite differences in evaluation by reporting location, there was no difference in the proportion of subjects who subsequently received a diagnosis of thyroid cancer, died from thyroid cancer, or died of any cause. Our findings suggest that radiology reporting methods and US guideline recommendations to evaluate all TI are likely contributing to the overdiagnosis of thyroid cancer. Future efforts to standardize reporting methods and alter guideline recommendations to not routinely evaluate all TI may mitigate overdiagnosis harms.
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