Influence of Incidental Detection of Thyroid Nodule on Thyroid Cancer Risk and Prognosis – A Systematic Review and Meta-analysis

Background Clinically inapparent thyroid nodules discovered serendipitously on imaging for non-thyroid indications are termed as thyroid incidentalomas. It is unclear whether these incidentalomas have a lower prevalence of malignancy or slower tumour progression compared to symptomatic nodules. The aim of this systematic review were to determine the impact of incidental detection of thyroid nodules on both the risk of malignancy and on prognosis in patients with thyroid cancer. Methods PubMed and MEDLINE® on Web of Science databases were searched from inception to April 2021 for English language articles reporting on human studies of thyroid cancer risk and/or prognosis in incidental and non-incidental nodules. Results Eighteen observational studies published between 1998 and 2020 were eligible for analysis; 4 studies reported on risk, 9 on prognosis and 5 studies reported on both risk and prognosis. When comparing the incidental and non-incidental groups in the risk study, the odds ratios calculated from the case control studies (n=6) ranged from 0.64 to 2.86; the relative risks calculated from the cohort studies (n=3) ranged from 0.13 to 6.27. A meta-analysis of the eligible case control studies (n=3) showed a non-significant summated odds ratio of 1.04 (95% CI=0.63–1.70, p=0.88). In the prognosis study, five direct and thirteen indirect markers of prognosis were compared between the incidental and non-incidental groups. A meta-analysis was not possible but incidentally detected thyroid cancer had better progression-free and overall survival. Conclusion Current evidence suggests that investigation and management of thyroid nodules should not be influenced by the mode of detection. However, incidentally detected nodules appear to have a better prognosis.