Large intrathymic parathyroid adenoma with hyperparathyroidism: a case report and review of the literature.

INTRODUCTION AND IMPORTANCE: Primary hyperparathyroidism is most commonly caused by a cervical parathyroid adenoma; however, ectopic mediastinal lesions may delay diagnosis when neck imaging is negative. CASE PRESENTATION: A 19-year-old woman presented with 4 years of progressive bone pain and osteoporosis with neuropsychiatric and gastrointestinal symptoms. Laboratory testing showed hypercalcemia (13 mg/dL) and markedly elevated PTH (614 pg/mL). Neck ultrasound and cervical CT were nondiagnostic. Technetium-99m sestamibi SPECT/CT localized a 38 × 40 mm hyperfunctioning lesion in the left anterior mediastinum. Initial video-assisted thoracoscopic surgery exploration failed to access the lesion; definitive resection was achieved via partial median sternotomy. Histopathology confirmed an intrathymic parathyroid adenoma. Postoperatively, calcium normalized and PTH decreased to 14 pg/mL with complete symptom resolution. CLINICAL DISCUSSION: This case highlights the diagnostic pathway for suspected ectopic parathyroid disease following negative cervical imaging and the need to individualize surgical access for deep mediastinal lesions. CONCLUSION: Mediastinal intrathymic parathyroid adenomas, although rare, should be considered in cases of persistent hyperparathyroidism with negative neck imaging. SPECT/CT is valuable for localization, and tailored surgical approaches can achieve a definitive cure.