A nonfunctioning parathyroid carcinoma misdiagnosed as a follicular thyroid nodule

Abstract

Parathyroid carcinoma (PC) is a rare endocrine malignancy. The tumor is mostly functioning, causing severe primary hyperparathyroidism, with high serum calcium and parathyroid hormone (PTH) levels. Nonfunctioning PC is extremely rare. We report a 50-year-old male patient who was referred to our Department for a right thyroid nodule, incidentally detected on carotid Doppler ultrasound scan, with a fine-needle aspiration cytology showing a follicular lesion. At the time of our evaluation, neck ultrasound showed a 1.3 cm right hypoechoic thyroid nodule with irregular margins and the absence of enlarged bilateral cervical lymph nodes. Thyroid function tests were normal. Serum calcium was normal and plasma PTH slightly above the upper limit of the normal range. The patients underwent right lobectomy. The intraoperative frozen-section pathological examination raised the suspicion of a PC. Definitive histology showed a markedly irregular infiltrative growth of the tumor with invasion of the thyroid tissue and cervical soft tissues. Immunostaining for thyroglobulin was negative, whereas staining for chromogranin A and PTH showed a strong reactivity. Based on the microscopic findings and the immunohistochemical profile, the tumor was diagnosed as a PC. Postoperative serum calcium and phosphate levels were in the normal range. One month after surgery, serum calcium and PTH were normal. Neck ultrasound and total body computed tomography scan were negative for local and metastatic disease. Eight months later, serum calcium was normal and plasma PTH level remained around the upper limit of normal range. Neck ultrasound did not show any pathological lesions. This is the first case of a nonfunctioning sporadic PC misdiagnosed prior of surgery as a follicular thyroid nodule. The parathyroid nature of the neck lesion could not be suspected before surgery. Fine-needle aspiration cytology (FNAC) may fail to distinguish a parathyroid tumor from a benign thyroid nodule because at FNAC, parathyroid and thyroid lesions have some morphological similarities. Histological criteria are not always sufficient for the differential diagnosis, which can definitely be established using immunohistochemistry.

Fine needle cytology pre‐surgical differentiation of parathyroid neoplasms: Is it reliable?

“…However, an accurate PN‐FNC diagnosis might be useful to determine the extent of surgery required. PN‐FNC advantages are highlighted when PN is located within the thyroid or in other abnormal locations . Many studies in the available literature focus on the FNC differentiation between PNs and thyroid neoplasms; in our and other experiences, this problem is generally overcome by clinical data.…”

“…As for cystic lesions, the functioning ones are classified as cystic PA and the non‐functional ones as simple parathyroid cysts . PN‐FNC is hampered by its cytological similarities to the more frequent thyroid follicular neoplasms, its relatively low incidence and by a scanty experience . Some skepticism from clinicians and the fear for tumor cell spread by FNC further enhance these difficulties .…”

“…FNC cannot discriminate among PA, PAA and PC . To the best of our knowledge, FNC differential diagnosis between PA and PC has never been reported, and PCs have been misdiagnosed on FNC because of their similarities to thyroid malignancies . In a series of 29 histologically proven PNs, two PCs were misdiagnosed by FNC as papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC) .…”

“…PN‐FNC features and diagnostic criteria have not been frequently described and some discordance has been reported; this is probably because of PN‐FNC rarity. PN‐FNC may be also hampered by an atypical localization and has probably been inhibited by the reported risk of occasional complications . Therefore, the main difficulties in PN‐FNC diagnosis concern their differentiation and classification.…”

Non-functioning parathyroid cystic tumour: malignant or not? Report of a case

“…An "en bloc" resection of the primary mass and surrounding tissues involved (adherent or infiltrated) is the widely accepted surgical option. The prognosis depends on the complete resection of the tumour: if the margins of resection are free of neoplastic tissue it is probable to obtain a good prognosis (5)(6)(7)(19)(20).…”