Papillary thyroid carcinoma (PTC) is the predominant thyroid malignancy, whereas atypical parathyroid tumor (APT) is rare, and ectopic localization further complicates detection. Persistent hypercalcemia with “normal-range” PTH can mask parathyroid pathology. We report a case of concurrent PTC and ectopic APT presenting with postoperative hypercalcemia, highlighting diagnostic pitfalls.

Single-patient case report with retrospective review of clinical data, biochemistry, imaging (neck ultrasound, fine-needle aspiration, sestamibi SPECT/CT, chest CT), operations (total thyroidectomy, bilateral cervical parathyroidectomy, and subsequent percutaneous endoscopic mediastinal excision), and histopathology including immunohistochemistry.

A 46-year-old woman with type 2 diabetes presented with polydipsia and intermittent headaches. Initial studies showed hypercalcemia (11.7 mg/dL), normal phosphate (2.9 mg/dL), inappropriately normal iPTH (38.6 pg/mL), 24-h urine calcium 358 mg/day, and 25(OH)D 25 ng/mL. Thyroid ultrasound revealed nodules; FNA was suspicious for PTC. She underwent total thyroidectomy and bilateral parathyroidectomy; pathology confirmed classic PTC without metastasis. Postoperatively, hypercalcemia persisted (11.6 mg/dL) with non-suppressed iPTH (22.2 pg/mL). Delayed sestamibi showed a subtle focus in the superior mediastinum; chest CT identified a 1.8cm paraesophageal mass. Percutaneous endoscopic excision achieved biochemical cure (calcium 8.9 mg/dL; iPTH 7.71 pg/mL). Histology demonstrated an atypical parathyroid tumor with a thick fibrous capsule and chief-cell morphology; immunostains were positive for chromogranin A, GATA-3, and PTH, confirming parathyroid origin. The patient was discharged on postoperative day 5 and entered routine follow-up.

In patients with persistent hypercalcemia after thyroid/parathyroid surgery, a “normal” PTH is physiologically inappropriate and should prompt evaluation for dual pathology and ectopic parathyroid disease. Subtle or focal scintigraphic uptake warrants targeted cross-sectional imaging (e.g., SPECT/CT, 4D-CT, or ^18F-fluorocholine PET/CT). Minimally invasive mediastinal excision can be curative.