Major Clues and Pitfalls in the Differential Diagnosis of Parathyroid and Thyroid Lesions Using Fine Needle Aspiration Cytology

Fine needle aspiration biopsy of parathyroid; is it meaningful? A cytologic study of 81 cases with histological and clinical correlations

BACKGROUND

Recognizing the parathyroid gland and distinguishing the parathyroid from thyroid lesions in fine needle aspiration (FNA) is challenging. This study aimed to identify cytomorphologic features suggestive of parathyroid origin and to assess the utility of cytopathology in conjunction with ancillary tests in the identification of parathyroid glands.

MATERIALS AND METHODS

Ultrasound (US) guided FNA of parathyroid gland and lesions in 81 patients were reviewed concerning clinical history and correlated to histopathologic findings in available cases. FNA smears were evaluated for cellularity, architectural patterns, cellular and nuclear features, and background of the smears. In 78 cases, FNA was supplemented by a measurement of parathormone (PTH) levels in the needle washout fluid (FNA-PTH assay) and/or GATA3/PTH/chromogranin-A immunostainings.

RESULTS

Sixty-four cases were diagnosed cytologically as parathyroid lesions in conjunction with FNA-PTH assay and/or immunocytochemical examinations. In an additional nine cases, a diagnosis of parathyroid lesions was rendered after repeated FNA with FNA-PTH assay. The histolopathologic diagnosis of surgically excised cases (n = 75) included parathyroid adenoma (60 cases), atypical parathyroid adenoma (4 cases), parathyroid hyperplasia (10 cases), and parathyroid carcinoma (1 case). Major cytological findings of parathyroid tissue included high cellularity, scattered naked nuclei, cribriform and three-dimensional clusters, stippled chromatin, and oxyphilic cytoplasm while papillary pattern or colloid-like material was identified in three cases respectively. No nuclear grooves or inclusions were seen in any case.

CONCLUSIONS

High cellularity scattered naked nuclei, cribriform and three-dimensional patterns, stippled chromatin and oxyphilic cytoplasm are cytomorphologic features that favour parathyroid origin. A combination of these features with FNA-PTH assay and/or GATA3, PTH, and chromogranin-A immunostainings on cytologic specimens aid in the identification of parathyroid glands and the distinguishing of parathyroid from thyroid lesions.

Remission of primary hyperparathyroidism after fine needle aspiration of a parathyroid nodule mistaken for a thyroid nodule

Primary hyperparathyroidism (PHPT) is an endocrine disorder characterized by hypercalcaemia and elevated or inappropriately normal concentrations of parathyroid hormone. Remission of PHPT caused by infarction or hemorrhage of a parathyroid adenoma rarely occurs, either spontaneously or induced, not always leading to a definitive cure. We report a case of 72-year-old women with primary hyperparathyroidism who underwent fine-needle aspiration cytology (FNAC) of a parathyroid adenoma mistaken for a thyroid nodule followed by normalization of parathyroid hormone (PTH) and serum calcium levels. Parathyroid origin was confirmed by immunohistochemistry. PTH levels began to rise at 4 months after FNAC demonstrating recurrence of the PHPT. This report shows that FNAC induced hemorrhage may cause remission of PHPT. Nevertheless, patient´s levels of PTH and serum calcium should be monitored, as remission may only be transitory.

Immunohistochemical Profile of Parathyroid Tumours: A Comprehensive Review

Immunohistochemistry remains an indispensable tool in diagnostic surgical pathology. In parathyroid tumours, it has four main applications: to detect (1) loss of parafibromin; (2) other manifestations of an aberrant immunophenotype hinting towards carcinoma; (3) histogenesis of a neck mass and (4) pathogenetic events, including features of tumour microenvironment and immune landscape. Parafibromin stain is mandatory to identify the new entity of parafibromin-deficient parathyroid neoplasm, defined in the WHO classification (2022). Loss of parafibromin indicates a greater probability of malignant course and should trigger the search for inherited or somatic CDC73 mutations. Aberrant immunophenotype is characterised by a set of markers that are lost (parafibromin), down-regulated (e.g., APC protein, p27 protein, calcium-sensing receptor) or up-regulated (e.g., proliferation activity by Ki-67 exceeding 5%) in parathyroid carcinoma compared to benign parathyroid disease. Aberrant immunophenotype is not the final proof of malignancy but should prompt the search for the definitive criteria for carcinoma. Histogenetic studies can be necessary for differential diagnosis between thyroid vs. parathyroid origin of cervical or intrathyroidal mass; detection of parathyroid hormone (PTH), chromogranin A, TTF-1, calcitonin or CD56 can be helpful. Finally, immunohistochemistry is useful in pathogenetic studies due to its ability to highlight both the presence and the tissue location of certain proteins. The main markers and challenges (technological variations, heterogeneity) are discussed here in the light of the current WHO classification (2022) of parathyroid tumours.