An unusual etiology of hyperparathyroidism: robotic-assisted resection of a giant functional intrathymic parathyroid cyst.

Parathyroid cysts (PCs) are relatively rare entities, with an even smaller proportion that functionally produce parathyroid hormone (PTH). Given associated hypercalcemia, often symptomatic, as well as potentially related osteoporosis and/or nephrolithiasis, resection of these functional cysts is often indicated. This case report details the management course for a patient who presented with primary hyperparathyroidism and was ultimately found to have a functional intrathymic PC. During initial workup, 4-dimensional computed tomography (4D-CT) of the neck demonstrated enlarged left upper and right lower parathyroid glands; however, the patient's hyperparathyroid state persisted even after bilateral neck exploration and resection of these two glands. Subsequent postoperative imaging of the mediastinum revealed a large (11 cm) thymic cyst. The patient consequently underwent uneventful robotic-assisted thoracoscopic excision of the mediastinal cyst. Intraoperative blood PTH levels dropped from 734 pg/mL preoperatively to 86 pg/nL 10 minutes following resection, consistent with surgical cure by the Miami Criteria. At two months postoperatively, the patient's serum total calcium (STC) was normal at 9.2 mg/dL. Final surgical pathology noted a 15-gram parathyroid gland, with cystic degeneration. As the robot becomes further integrated into the everyday practice of thoracic surgery, we believe this approach offers advantages over conventional video-assisted thoracoscopic surgery (VATS) for mediastinal resections. Advantages include better visualization and finer, more precise dissection, especially important in this case, given the proximity of vital structures and the small, but real, risk of parathyromatosis associated with intraoperative cyst rupture.