McCoy and colleagues report their findings in 48 patients who had FPCs (n = 41) or NPCs (n = 7). As they mention in their article, finding more FPCs than NPCs differs from most other articles in the literature. This is obviously because patients were referred to this excellent group of endocrine surgeons for their expertise in treating patients who have primary hyperparathyroidism.
What is the usual presentation of patients with parathyroid cysts? Patients with NPCs usually have a large cystic mass (median, 5.0-cm diameter in this series) as observed by physical examination or ultrasonography or at operation. Fine-needle aspiration usually (65% [13 of 20 patients] in this series) reveals clear colorless fluid. Such fluid is virtually pathognomonic for parathyroid cysts. Parathyroid hormone assay of the cyst fluid can confirm the diagnosis, although it is probably unnecessary when the fluid of a cyst is clear and colorless. When cyst fluid is yellow or turbid, however, assaying for PTH level certainly can establish the correct diagnosis. Most articles in the literature suggest using a midregional or C-terminal assay rather than an N-terminal PTH assay, because midregional assays are more likely to confirm the diagnosis.
Clark OH. Cystic Parathyroid Lesions—Invited Critique. Arch Surg. 2009;144(1):56. doi:10.1001/archsurg.2008.506