Contribution of Hybrid SPECT/CT Dual-Tracer Imaging with Na[⁹⁹ᵐTc]TcO₄ / [⁹⁹ᵐTc]Tc-MIBI in the Diagnosis of a Mediastinal Ectopic Parathyroid Adenoma

Introduction: Primary hyperparathyroidism is the third most common endocrine disorder, affecting women 2 to 3 times more frequently than men. In 80% of cases, it is caused by a parathyroid adenoma. In 15–20% of cases, the parathyroid adenoma is ectopic, resulting from aberrant embryological migration. Mediastinal localization is less common, representing 10–15% of ectopic parathyroid adenomas. Dual-tracer scintigraphy using technetium-sestamibi and technetium pertechnetate improves the sensitivity for detecting parathyroid adenomas. The aim of this study was to demonstrate the contribution of dual-tracer hybrid imaging in the diagnosis of an ectopic parathyroid adenoma. Case Report: We report a patient whose biological assessment revealed hypercalcemia (11.1 mg/dL) associated with elevated serum parathyroid hormone (PTH) levels (258 pg/mL), suggesting a parathyroid adenoma. Initial cervical ultrasonography failed to identify a suspicious parathyroid lesion. Hybrid SPECT/CT imaging revealed a 12 × 10 mm hypodense nodule located in the right retrosternal region, compatible with a parathyroid adenoma. Conclusion: The high sensitivity of hybrid imaging allowed the detection of an ectopic parathyroid adenoma and facilitated precise preoperative localization. However, in cases of diagnostic uncertainty, fluorocholine PET/CT has been shown to be more sensitive and more specific.