Coexistence of a large functioning parathyroid cyst with papillary thyroid carcinoma: A case report and review of the literature.

Parathyroid cysts constitute a rare cause of primary hyperparathyroidism (PHPT). PHPT may also rarely coexist with non-medullary thyroid carcinoma (NMTC). We describe a case of a 70-year-old woman who was diagnosed with PHPT, on the occasion of nephrolithiasis (corrected calcium and PTH levels: 10.8 mg/dl and 187 pg/ml, respectively). Ultrasonographic and scintigraphic investigation confirmed the diagnosis of a large parathyroid cyst attached to the lower pole of the right thyroid lobe and, consequently, the patient underwent parathyroidectomy. Due to the coexistence of multinodular goitre, with some nodules characterized as suspicious of malignancy, a total thyroidectomy was also performed. A histological diagnosis of cystic parathyroid adenoma was made. A unifocal papillary thyroid carcinoma of follicular subtype, 6 mm in diameter, was also detected. The patient's post-surgical course was uneventful and she remained normocalcaemic two years later. PHPT may rarely coexist with papillary thyroid carcinoma (PTC). The pathogenetic mechanisms linking these two endocrine entities are currently unknown.