A Case of Nonfunctional Parathyroid Cyst Diagnosed Preoperatively by Analysis of the Cyst Aspirate for Parathyroid Hormone

Abstract

Parathyroid cysts are classified into two categories, nonfunctional cysts and functional cysts. It is difficult to distinguish nonfunctional parathyroid cysts from thyroid cysts preoperatively, because the serum levels of parathyroid hormone (PTH) and calcium are within the reference values even in patients with nonfunctional parathyroid cysts. As a result, some cases of nonfunctional cysts are actually diagnosed as thyroid cysts and treated by hemithyroidectomy.

We report a case of a nonfunctional parathyroid cyst that was diagnosed preoperatively by analysis of the cyst fluid and treated by surgical excision. A 38-year-old woman was admitted to our hospital for the treatment of trachelophyma. Ultrasonography revealed a cystic mass located in the inferior pole of the left lobe of the thyroid. The serum levels of PTH and calcium were within the reference values. Fine needle aspiration biopsy of the cyst was performed under the guidance of ultrasonography. The cyst fluid was clear and colorless, and showed elevated levels of intact PTH (i-PTH) (1790 pg/mL). Therefore, we diagnosed the cyst as a parathyroid cyst. After follow-up of the patient for 3 years, surgical excision of the cyst was performed because of enlargement of the cyst and presence of evidence of the compression syndrome. Histopathological examination of the surgical specimen revealed a parathyroid cyst. After operation, the patient developed no complications such as recurrent laryngeal nerve paralysis, hypothyroidism, or hyperparathyroidism. Surgical excision of the cyst is preferable to hemithyroidectomy for the treatment of parathyroid cysts, because hemithyroidectomy is associated with a higher risk of postoperative recurrent laryngeal nerve paralysis and hypothyroidism.

Analysis of the i-PTH level in aspirates from the cysts is potentially useful for preoperative diagnosis of nonfunctional parathyroid cysts.