Peculiar Presentation of an Intrapericardial Ectopic Thyroid

Background and Clinical Significance: Intrapericardial ectopic thyroid tissue is extremely rare and can mimic vascular mediastinal or cardiac lesions. Case Presentation: We describe a 62-year-old woman with dyspnea, palpitations, and flushing for several months, progressively worsening, associated with nonspecific ST-segment abnormalities on ECG. Contrast-enhanced CT revealed a small, highly vascularized epicardial mass anterior to the ascending aorta. 18F-FDG PET/TC findings were inconclusive, and biopsy was not feasible due to the anatomical location. Surgical excision via upper ministernotomy was performed, leading to resolution of symptoms. Histology confirmed benign ectopic thyroid tissue. Conclusions: With fewer than ten similar intrapericardial cases reported in the English-language medical literature, this presentation underlines the diagnostic difficulty of such lesions and the importance of including ectopic thyroid tissue among the less common differential diagnostic considerations for intrapericardial masses, particularly in patients with prior thyroid disease.