Mediastinal parathyroid adenoma: diagnostic and therapeutic challenges

Mediastinal parathyroid adenomas (MPAs) represent an uncommon but clinically important cause of persistent or recurrent primary hyperparathyroidism. Though most cases of sporadic primary hyperparathyroidism are due to a parathyroid adenoma in the cervical area; ectopic glands account for a fifth of cases, with only 1-2% situated in the mediastinum. Aberrant embryological descent of the inferior parathyroid glands along the thymic descent pathway gives rise to MPAs, with variable locations within the anterior or posterior mediastinum. The anatomical variability, coupled with limited accessibility is a major contributor to diagnostic uncertainty and surgical failure, especially in reoperative cases. Accurate preoperative localization using multimodal imaging is essential for optimal management of the condition. Whilst the dual modalities of imaging, namely the ultrasound scan and technetium-99m sestamibi scintigraphy are useful in cervical lesions, the sensitivity of picking up adenomas especially the small and cystic lesions in the mediastinum is quite low. Four-dimensional computed tomography (4D-CT) provides high spatial resolution and characteristic enhancement kinetics that are particularly useful in ectopic or reoperative settings, albeit at the cost of higher radiation exposure. Positron emission tomography/computed tomography (PET-CT) using 18F-fluorocholine demonstrates high sensitivity in negative or discordant first-line imaging and is increasingly adopted where available. Where non-invasive modalities fail, invasive techniques like selective venous sampling may localize mediastinal lesions but requires expertise and careful interpretation of variant venous drainage. Intervention with surgical excision via the cervical approach is possible when the MPAs are located above the innominate vein. Historically the deeper locations required access with sternotomy or thoracotomy, but with the advent of minimally invasive thoracic approaches, higher cure rates with minimal morbidity are possible, coupled with adjuncts such as intraoperative parathyroid hormone monitoring (IOPTH) and fluorescence techniques. Ongoing challenges include discordant imaging, multiglandular disease, resource limitations, and reoperative complexity, underscoring the need for stepwise imaging escalation and multidisciplinary approach to optimize outcomes.