Ultrasound guided fine needle aspiration biopsy of parathyroid gland and lesions

BACKGROUND: Parathyroid gland and their tumors comprise a small proportion of non-palpable neck masses that are investigated by ultrasound (US) guided fine needle aspiration biopsy. We reviewed our institution's cases of US guided FNAB of parathyroid gland and their lesions to determine the role of cytology for the preoperative diagnosis of parathyroid gland and their lesions. METHOD: All cases of FNAB of parathyroid gland and lesions in the last 10 years were reviewed in detail with respect to clinical history and correlated with the histopathologic findings in available cases. The cytologic parameters that were evaluated included cellularity assessed semiquantitatively as scant, intermediate or abundant (<50, 51–500 or >500 cells), cellular distribution (loose clusters, single cells/naked nuclei, rounded clusters, two- and three-dimensional clusters, and presence of prominent vascular proliferation), cellular characteristics (cell size, nuclear shape, presence/absence of a nucleolus, degree of mitosis, amount of cytoplasm, and appearance of nuclear chromatin), and background (colloid-like material and macrophages). Immunostaining for parathyroid hormone (PTH) was performed on selected cases using either destained Pap smears or cell block sections. RESULTS: Twenty cases of US-guided FNAB of parathyroid glands and their lesions including 13 in the expected locations in the neck, 3 in intrathyroid region, 3 in thyroid bed, and 1 metastatic to liver were studied. Majority of the cases showed intermediate cellularity (51–500 cells) with round to oval cells that exhibited a stippled nuclear chromatin, without significant pleomorphism or mitotic activity. The cells were arranged in loose two dimensional groups with many single cells/naked nuclei around the groups. Occasionally macrophages and colloid like material was also encountered. There was no significant difference in the cytomorphologic features between normal gland, hyperplasia adenoma, or carcinoma. Immunocytochemical analysis for PHT was performed for 14 cases (6 destained smears and 8 cell blocks) which showed distinct cytoplasmic positivity. CONCLUSION: US-guided FNAB is a useful test for confirming the diagnosis of not only clinically suspected parathyroid gland and lesions but also for detecting parathyroid glands in unexpected locations such as in thyroid bed or within the thyroid gland. Although there is significant overlap in the cytomorphologic features of cells derived from parathyroid and thyroid gland, the presence of stippled nuclear chromatin, prominent vascular proliferation with attached epithelial cells, and frequent occurrence of single cells/naked nuclei are useful clues that favor parathyroid origin. Distinction of the different parathyroid lesions including hyperplasia, adenoma, and carcinoma cannot be made solely on cytology. Immunostaining for PTH can be performed on destained Pap smears and cell block sections which can be valuable for confirming parathyroid origin of the cells.