Ectopic Parathyroid Gland Mimicking Mediastinal Tumor

Abstract

The role of endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) in the evaluation of mediastinal masses has increased since its introduction in 1991. The ability of EUS-FNA to diagnose masses accurately can prevent unnecessary surgeries for patients with benign masses. We present a case of a rare type of mediastinal mass discovered via cross-sectional imaging and subsequent evaluation using EUS-FNA. A 79-year-old Caucasian female with past medical history significant for coronary artery disease presented with complaints of retrosternal chest pain. During her workup, a chest CT scan showed thickening of the upper-esophagus with a 23mm x 20mm, rounded, soft tissue density near the left posterolateral aspect of the esophagus. Given the concern for esophageal malignancy, an upper endoscopy was performed which did not show any significant intraluminal abnormalities. Subsequent endoscopic ultrasound revealed a 26mm x 9.5mm hypoechoic, homogenous mass in the posterior-superior mediastinum. Fine needle aspiration was performed and cytology results revealed bland appearing follicular cells and watery proteinaceous material. Cell block staining was positive for Cytokeratin (AE1/AE3), Chromogranin, and Parathyroid Hormone consistent with ectopic parathyroid tissue. Mediastinal masses can present a diagnostic challenge as the clinical manifestations and imaging features are often not sufficient to establish a conclusive diagnosis. EUS-FNA has been shown to be a safe and accurate means of obtaining a tissue diagnosis for these mediastinal masses. Studies have shown that EUS-FNA alters the therapeutic plan for up to 68% of patients. In a study of patients undergoing EUSFNA for abdominal/mediastinal masses, 16% of patients were able to avoid unnecessary surgery, as was the result in this case. Among the etiologies for mediastinal masses, ectopic parathyroid tissue (EPT) is an uncommon finding. EPT is a developmental abnormality involving aberrant embryogenesis of the parathyroid gland during its passage from the floor of the primitive foregut to its final pre-tracheal position. Previous studies have shown that between 6-16% of parathyroid glands are found in an ectopic position due to abnormal embryogenesis or the presence of more than four parathyroid glands. This case demonstrates the important role that EUS-FNA plays in preventing unnecessary surgical interventions for benign mediastinal masses.Figure 1Figure 2Figure 3