Clinical Characteristics, Diagnostic Approach and Outcome of Thyroid Incidental Findings vs. Clinically Overt Thyroid Nodules: An Observational Single-Centre Study

Simple Summary Thyroid nodules are common and can present as visible, palpable or symptomatic nodules (non-incidentalomas) and as coincidental findings on imaging techniques (so-called incidentalomas). The majority are benign but recognizing clinically relevant nodules remains a challenge. Dutch guidelines currently recommend to refrain from additional diagnostic testing in incidentalomas other than FDG-PET-incidentalomas. However, there is no consensus on, or data of, the outcome of the further approach. Our retrospective observational study aims to compare clinical characteristics and outcome between patients with incidentalomas and non-incidentalomas. We found that the risk of malignancy in incidentalomas found on other modalities than FDG-PET was significantly lower (2.8%) than FDG-PET-incidentalomas (11.8%) or non-incidentalomas (11.1%). Furthermore, incidentalomas were significantly smaller than non-incidentalomas. Our findings support the current recommendations to prioritize additional analysis to non-incidentalomas, FDG-PET incidentalomas and clinically relevant non-PET-incidentalomas. These findings are relevant to avoid unnecessary diagnostic testing and therapy and therefore possible harm to patients. Context: Thyroid nodules are common and can present as clinically overt nodules (visible, palpable or symptomatic nodules) and so-called incidentalomas (coincidental findings on imaging techniques). The majority are benign but recognizing clinically relevant nodules remains a challenge. Current Dutch guidelines recommend to refrain from additional diagnostic testing in incidentalomas other than FDG-PET-incidentalomas, unless there are suspicious clinical and/or sonographic features. However, there is no consensus on the further approach and no "real-life" data on the outcome of such an approach. Objective: To compare clinical characteristics, diagnostic approaches and clinical outcome between patients referred with thyroid incidentalomas and non-incidentalomas at one academic referral thyroid clinic. Methods: Clinical and demographical characteristics, diagnostic and therapeutic approaches and outcome were retrospectively obtained from the files of all patients newly referred because of thyroid incidentalomas or non-incidentalomas to our institution (between March 2011 and January 2017). Subsequently, the data were compared between both groups. Results: In total, 351 patients (64.3%) were referred because of non-incidentalomas and 195 (35.7%) because of incidentalomas. Incidentalomas were smaller (48.7% <2 cm) than non-incidentalomas (23.4% <2 cm). Furthermore, incidentalomas were less often symptomatic (15.9 vs. 42.7% p < 0.001). Fine-needle aspiration was performed in a similar percentage of the patients in the two groups (62.6% of incidentalomas vs. 69.8% in non-incidentaloma, p = 0.08). Significantly less malignancies were found among incidentalomas compared to non-incidentalomas (5.1% vs. 11.1%, p = 0.019). Moreover, significantly more malignancies occurred in PET-incidentalomas than non-PET-incidentalomas (11.8% vs. 2.8%, p = 0.023). In fact, the proportion of malignancies in PET-incidentalomas and non-incidentalomas was similar (11.8% vs. 11.1%, p = 0.895). Stability or decrease in size was observed in 96.5% of nodules receiving ultrasound follow-up. Conclusions: Patients with small asymptomatic thyroid incidentalomas represent an important proportion of the patients referred for additional diagnostic evaluation. The risk of malignancy in these patients is lower than in those with symptomatic palpable lesions, particularly in the patients with incidentalomas discovered on CT, MRI or US. Our findings support the current recommendations from the Dutch guidelines to not indiscriminately perform additional analysis and treatment on all incidentalomas, but prioritize this to FDG-PET-incidentalomas and clinically relevant non-PET-incidentalomas. Moreover, US features can further refine the selection of the patients who require immediate FNAC and/or surgery.