Non-functioning parathyroid cystic tumour: malignant or not? Report of a case.

Parathyroid carcinoma (PC) is a very rare endocrine tumour, usually characterized by symptoms such as a neck mass, dysphonia, severe hypercalcemia exceeding 140 mg/L and elevated serum parathyroid hormone levels, even more than 5 times the upper limit of normal. Non-functioning parathyroid cancer is extremely rare and, in this case, its pre-operative diagnosis is often difficult. A 54-year old female patient, referring dysphagia and dysphonia, underwent neck ultrasound and neck CT. A left thyroid nodule, probably cystic, was found. It presented caudal extent on anterior mediastinum causing compression of the left lateral wall of the trachea. The preoperative calcemia was into the normal range. The patient underwent left thyroid lobectomy. Histological exam showed a cystic lesion, immunohistochemically originating from parathyroid that oriented for carcinoma. The 18 months follow-up did not show a residual-recurrent disease. The parathyroid origin of a neck lesion could not be suspected before surgery when specific laboratory tests are not available and clinical effects of hyperparathyroidism syndrome are not present. Histological features are not always sufficient for the differential diagnosis between the parathyroid adenoma and carcinoma. The immunohistochemistry is an useful tool that can aid to reach the definite diagnosis.