ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2017) 49 GP242 | DOI: 10.1530/endoabs.49.GP242

False negative fine needle aspiration thyroid cytology: an institutional experience

Anabela Martins, Evelina Mendonça, António Garrão, Hugo Marques, Maria Cid, Francisco Rosário, Ricardo Veiga & Ana Catarino

Hospital da Luz, Lisbon, Portugal.

Introduction: Fine needle aspiration cytology (FNA) is the most accurate diagnostic method for thyroid malignant nodule diagnosis. According to the literature, the percentage of false negative results (FN-FNA) is less than 1.5%, in tertiary health care centers.

In this study we describe the cases reported in this Hospital, between 2014 and 2016, of benign cytology, histologically characterized as malignant. All pathologic specimens were reviewed.

Results: From a total of 299 benign FNA cases submitted to surgery, 6 cases with malignant histopathology were detected (2.0%). FN-FNA was identified in 5 males and 2 females, with ages ranging from 42 to 72 years old. The nodules size varied between 41 to 95 mm.

The ultrasound malignancy risk was between 5 and 20% (ATA 2015 Risk Stratification System).

The benign FNA were described as hyperplasic nodule in 3 cases, cystic hyperplasic nodule in 1 case, cystic colloid nodule in 1 case and colloid nodule in the remaining.

In all the cases the histological diagnosis was of follicular variant of papillary carcinoma, with macrofollicular areas, either predominant or focally, and with a heterogeneous distribution of the distinctive nuclear features of papillary carcinoma.

Four patients were recommended for radioiodine therapy. One of these patients was diagnosed with pulmonary and bone metastases.

Four patients were available for follow-up (mean time =1.5 years; 9–24 months). There is no imaging evidence of disease in any of the patients.

Conclusions: In our institution, the percentage of FN-FNA was 2.0%, in accordance with that described in the literature.

The ultrasound risk assessment did not significantly change the risk assessed by FNA.

In all the cases the histological diagnosis was follicular variant of papillary carcinoma. The presence of macrofollicular areas, cystic areas and a heterogeneous expression of the typical nuclear features of papillary carcinoma may explain the occurrence of FN-FNA.

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