Intrathyroidal thymic tissue: a pediatric case series from a secondary care center.

Intrathyroidal ectopic thymus (IET) is a benign condition caused by aberrant thymic migration during embryogenesis. Often detected incidentally on ultrasound (US), it can mimic malignant thyroid nodules, leading to unnecessary interventions. We aimed to define the imaging characteristics of IET and emphasize an accurate diagnosis to avoid unwarranted procedures. We describe 5 pediatric cases of IET diagnosed by cervical US and monitored through long-term serial imaging. All lesions appeared as intrathyroidal nodules with echogenicity and internal foci typical of thymic tissue. Follow-up imaging showed no significant changes. None of the patients had thyroid dysfunction or clinical symptoms. The distinctive sonographic features of IET can differentiate it from malignant nodules, preventing unnecessary biopsies or surgeries. US follow-up confirmed a benign course and supports conservative management strategies.