ESPE Abstracts

Background: Intrathyroidal ectopic thymus (IET) represents a relatively rare embryologic anomaly, often discovered incidentally in paediatric patients. The long-term outcome of IET is not completely clear and differentiation from thyroid nodules is crucial to prevent invasive diagnostic procedures and/or unnecessary surgical interventions. This prospective observational study aims to elucidate the clinical characteristics, diagnostic workup, and long-term outcome associated with IET in a paediatric population.

Methods: A prospective cohort of children presenting with incidentally discovered IET was enrolled over a 15-year period and followed up longitudinally. Comprehensive data collection included family and clinical history, anthropometric parameters, thyroid ultrasonographic data (US), thyroid function and autoimmunity.

Results: Data at baseline of 65 patients (65% males, 35% females) were analysed. All IET were detected incidentally at US during routine screening or evaluation for supected autoimmune thyroiditis. No child had a palpable thyroid nodule. Median age at first visit was 5.7 years [IQR 4.5-8.1]. Initially, US showed hypoechoic solid lesions with punctate and linear echogenicity. The maximal median dimension of IET at baseline was 7.5 mm [IQR 5-9]. At baseline evaluation, IET was found in 29% of cases in the right lobe and 56.9% in the left lobe. In 4.6% of cases IET were detected in both thyroid lobes. Re-evaluation was performed at least once in 58 patients after diagnosis, with a mean follow-up time (FU) of 3.6 years. The lesion was considered to decrease in size if there was a reduction equal to or greater than 1 mm in any dimension. A complete regression of IET was observed in 20% of patients during FU. Median FU was 5.9 years [IQR 3.2-8.5]. In 80% of cases IET did not resolve completely. A median decrease in size of 1.5 mm [IQR 1.0-3.0] was observed after a median FU of 3.2 years [IQR 1.4-4.4]. Final US showed changes to hyperechoic patterns and blurred margins. No patient showed increase in size or malignant transformation of IET.

Conclusion: The results of this prospective observational study contribute to the understanding of the clinical course of intrathyroidal thymic inclusions in paediatric patients. Our findings confirm the benign and self-limiting nature of IET, characterised by spontaneous involution with age. Finally, the results indicate that close FU or aggressive interventions should not be recommended in these cases.