DOI: https://doi.org/10.36347/sjmcr.2026.v14i02.030

Pages: 300-304

Background: Thyroid heterotopia, also known as ectopic thyroid tissue, is a rare congenital anomaly characterized by the presence of normal thyroid parenchyma outside its usual pretracheal location, coexisting with a normally positioned and structured orthotopic thyroid gland. It results from an abnormality in the embryological migration and maturation of thyroid tissue. While often asymptomatic and discovered incidentally, it can occasionally present as a palpable mass, leading to diagnostic challenges. Technetium-99m pertechnetate (99mTcO4-) scintigraphy is the functional imaging modality of choice, offering high sensitivity and specificity for localizing functional thyroid tissue. Case Presentation: We report the case of a 60-year-old woman with no significant past medical history, who presented with a two-month history of a gradually enlarging, painless right supraclavicular swelling. She was clinically and biochemically euthyroid, with a normal TSH level of 3.80 µU/mL. Cervical ultrasound revealed an extra-thyroidal, solid supraclavicular mass located adjacent to the lower portion of the right internal jugular vein, with echostructure similar to normal thyroid parenchyma. The orthotopic thyroid gland itself was normal in position, size, and morphology. Contrast-enhanced computed tomography (CT) of the neck confirmed a well-defined, enhancing right supraclavicular mass, which appeared contiguous with the right thyroid lobe, initially raising suspicion for a pedunculated thyroid nodule. To resolve the diagnostic uncertainty, a 99mTc-pertechnetate thyroid scintigraphy was performed following intravenous injection of 5 mCi (185 MBq) of the radiotracer. The scan revealed a focus of intense radiotracer uptake ("hot nodule") projecting into the right superior mediastinum, clearly separate from but functionally concordant with the normally positioned, well-visualized orthotopic thyroid gland. This confirmed the diagnosis of functional ectopic thyroid tissue (thyroid he