Diagnostic pitfalls in parathyroid gland cytology

The aim of this study is to establish possibilities of using cytology in the diagnosis of parathyroid gland adenoma. 475 patients, all suspected to have parathyroid gland disease, were examined over a three-year period (from 1 of January 2006 to 31 of December 2008) in the Clinical Department of Nuclear Medicine and Radiation Protection, University Hospital Center Zagreb, Croatia. Ultrasound guided fine needle aspiration biopsy (UG-FNAB) of suspected occurrences determined by ultrasound was done. Samples obtained by UG-FNAB were air-dried and stained using the May-Grünwald-Giemsa (MGG) staining procedure. PTH levels were determined in all punctate and sera obtained on the day of UG-FNAB. Samples adequate for cytological analysis were obtained from 288 patients, while 187 punctates did not contain epithelial elements. The parathyroid hormone (PTH) analysis was made for all punctates. The adenoma was diagnosed via morphological characteristics in 71 out of 288 punctates that were proven adequate for cytological analysis. Increased PTH levels were later on established in all diagnosed adenomas. All patients with cytology-based diagnosis of parathyroid gland adenoma were sent to surgery, and the cytological diagnosis was confirmed by pathohistology. In three cases, the parathyroid gland adenoma was established by pathohistology, although in these cases the cytological diagnosis was negative. The cytological diagnosis of parathyroid gland adenoma can be considered reliable in 96% of cases, provided that the echosonographic structure and localisation of the punctured node is noted, and assuming that material adequate for cytological analysis is obtained by FNAB. Possible pitfalls are oncocytic types of parathyroid adenoma, intranuclear inclusions and papillary formation of epithelial cells, and cystic degeneration of nodules. These errors can be avoided by defining the PTH level on the same punctate.