Fine‐needle aspiration cytology of an intrathyroid parathyroid adenoma

Dear Dr. Bedrossian: A 70-year-old woman with an unremarkable medical history was referred to an endocrinologist by her family physician, for investigation of a possible hyperparathyroidism. By physical examination, a 2-cm solitary thyroid nodule (TN) was found in her right thyroid lobe. Routine blood work and urine analysis showed no abnormality. Her serum biochemical tests revealed a slight hypercalcemia and an increased level of parathyroid hormone. A thyroid scintigraphic scan confirmed the presence of an ovoid, solid, and ‘‘cold’’ intrathyroid nodule measuring 2 cm in greatest dimension located within her right thyroid lobe. The thyroid gland showed no other abnormal imaging finding, and no extra-thyroid mass lesions were found. An intrathyroid parathyroid adenoma was suspected and a fine-needle aspiration (FNA) of her TN was performed under ultrasonographic guidance, using a 22-gauge and 4.5-cm-long needle connected to a 10-ml plastic syringe. Four direct smears were prepared from the needle aspirate, air-dried, and stained by the Diff-Quick method. The thyroid needle aspirate was cellular and showed a small amount of diluted colloid. There were several sheets and syncytial clusters of small epithelial cells with scant, illdefined, granular cytoplasm, and uniformly oval nuclei. Nuclear crowding and overlapping were present, and in some cell clusters, a vague acinar arrangement was present. There were also a few epithelial cells showing poorly-formed intranuclear cytoplasmic inclusions (INCI) (Fig. 1). Scattered single bare nuclei that were morphologically similar to those of the above-described epithelial cells were present in the smear background. The cytologic findings were suggestive of a thyroid microfollicular neoplasm. However, a parathyroid adenoma or a papillary carcinoma was not ruled out. Two cellular Diff-Quikstained smears were stained, without prior destaining, with commercial thyroglobulin and parathyroid hormone antibodies, by the avidin–biotin complex (ABC) technique, respectively. The epithelial cells present reacted positively with thyroglobulin and equivocally negatively with parathyroid hormone antibodies. The patient’s TN was judged to be a follicular-variant papillary carcinoma, and she subsequently underwent a surgical cervical exploration. At surgery, no enlarged parathyroid glands were found, and the patient’s TN was removed by total thyroidectomy. Histologic examination of the thyroid revealed an encapsulated intrathyroid tumor measuring 2 cm in greatest dimension. It consisted of cuboidal cells with round or oval nuclei and scant or granular cytoplasm arranged in acinar pattern, and occasional cells displayed INCIs (Fig. 2). In no place, a papillary formation of the neoplastic epithelial cells was observed. The histologic pattern of the lesion was suggestive of an intrathyroid parathyroid adenoma. Five-micron-thick tumor tissue sections from a representative tumor fragment were stained with commercial antibodies against thyroglobulin and parathyroid hormone by the ABC technique. The tumor cells reacted positively with parathyroid hormone and negatively with thyroglobulin antibodies. The histologic and immunohistochemical features of the patient’s TN were in keeping with an intrathyroid parathyroid adenoma. The rest of the thyroid gland showed three separated minute follicular-variant papillary carcinomas ranging from 1 to 2.5 mm in greatest dimensions, two in the left lobe and one in the right lobe. None of those papillary carcinomas showed hemorrhagic necrosis to suggest a previous sampling by FNA. This brief communication reported an intrathyroid parathyroid adenoma with interesting aspiration cytology and misleading immunocytochemical staining results. From the cytodiagnostic point of view, several cases of parathyroid adenoma with cytologic evaluation by FNA have been reported in recent years. In almost all reported cases, the FNA revealed abundant bare nuclei, epithelial cells with scant, ill-defined cytoplasm, and oval nuclei arranged in acini and in syncytial sheets displaying nu-