Prevalence of parathyroid cysts by neck ultrasound scan in unselected patients.

BACKGROUND: Parathyroid cysts (PC) are a rare entity, representing only 0.5-1% of all parathyroid lesions and <1% of neck masses. Since its first description, in the second half of the 19th century, fewer than 300 cases have been reported. By reviewing the literature, it appears that the data available arose from surgical series, and the precise incidence of PC as detected by ultrasound (US) has not been described. The aim of this study was to review 5 yr of routine neck US, mainly performed for thyroid diseases, in order to estimate the prevalence of PC in a large series of patients. METHODS: We reviewed our database of neck US investigations performed from 2003 to 2007: all data regarding patient's clinical history, US images, and fine needle aspiration cytology were retrospectively collected. RESULTS: Among 6621 patients submitted to neck US investigation, a PC (mean diameter 36.4+/-14.2 mm; range 25-61 mm) was diagnosed in 5 cases. Serum PTH levels were high in all the patients (221+/-140.7 pg/ml; range 111-456 pg/ml), whereas serum calcium levels only in 3 subjects (10.8+/-1.4 mg/dl; range 9.2-12.9 mg/ml). CONCLUSION: This is the first study evaluating the prevalence of PC in a large series of unselected patients by US. Our results demonstrate a much lower incidence (0.075%) of incidentally detected PC than previously reported.