Fine-Needle Aspiration Cytology of Parathyroid Lesions

Abstract

Parathyroid tissue is not uncommonly encountered in evaluation of "thyroid nodules," either due to radiologic misinterpretation of a parathyroid neoplasm as thyroidal in origin or due to incidental sampling during aspiration of a thyroid nodule. Recognition of the cytologic features of parathyroid is important to prevent misdiagnosis of these relatively common lesions and subsequent inappropriate surgical management. In addition, fine-needle aspiration is occasionally used in the preoperative workup of patients with hyperparathyroidism. Fine-needle aspiration can be used as an adjunct to imaging for preoperative localization of hyperfunctioning parathyroid tissue, which helps to minimize the extent of surgical exploration. This report reviews the cytomorphologic features of parathyroid lesions, differential diagnostic considerations, and ancillary methods that can be used to arrive at the right diagnosis.A 39-year-old man with history of papillary thyroid cancer treated with total thyroidectomy and subsequently 131 iodine and end-stage renal disease secondary to hypertensive nephropathy presented for surveillance 4 years after initial diagnosis. He underwent positron emission tomography/computed tomography that showed an area of increased metabolic activity in the anterior superior mediastinum, which was excised and found to be thymic tissue. A subsequent ultrasound examination performed a few months later revealed that the right thyroid bed contained an area of soft tissue echogenicity measuring 5 Â 7 Â 8 mm. Because of suspicion of recurrent papillary thyroid carcinoma, the nodule was targeted for fine-needle aspiration (FNA). With ultrasound guidance, the nodule was aspirated using a 25-gauge needle. Smears were air dried and stained with a modified Giemsa stain, and after the aspirate was deemed adequate, the rest of the smears were alcohol fixed and stained with Papanicolaou stain.Cytologic examination revealed a hemorrhagic, mildly cellular smear containing small round cells, which formed loosely cohesive clusters (Fig. 1). Single cells and naked nuclei were present. The cells had monomorphic, small, round nuclei with fine chromatin. The cytoplasm was moderate in amount and granular. There was sufficient material in the needle rinse to prepare multiple cytospin slides, on which immunocytochemistry was performed. The cells were positive for parathyroid hormone (PTH) and chromogranin A and negative for thyroglobulin and TTF-1. A diagnosis of parathyroid lesion was rendered.Subsequent review of medical records revealed a normal serum calcium level. No serum PTH assays were performed. The patient was presumed to have subclinical parathyroid enlargement secondary to renal failure.

Parathyroid Cytology: A Diagnostic Dilemma

“…Parathyroid lesions can be incidentally encountered during FNA of a thyroid nodule. [1] Superior and inferior parathyroid glands embryologically develop from IV and III pharyngeal pouches respectively. [2] It is difficult to distinguish thyroid nodules from parathyroid nodules clinically especially if it is intrathyroidal/subcapsular location.…”