Endocrine Abstracts

Background: Distinguishing the malignant follicular-type thyroid neoplasm (FTTN), i.e. follicular carcinoma (FTC) and follicular-variant papillary carcinoma (FVPTC), from their benign counterparts, i.e. follicular adenoma (FA) and non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), is challenging without surgical resection. As thyroid nodules are increasingly diagnosed asymptomatically, an accurate way of confirming benignity of FTTN can reduce excessive diagnostic surgery.

Objective: to determine the clinical, demographic, sonographic, and cytologic differences between the malignant and benign FTTN

Methods: We retrospectively reviewed the medical records of all patients who underwent thyroidectomy in a tertiary-care hospital in Singapore from 2010 to 2016, and identified all FTTN that underwent fine-needle aspiration cytology preoperatively. We matched the sonographic images of the FTTN to their histologic diagnosis. Blinded to the diagnoses, two head and neck radiologists independently reviewed the images and classified them per Thyroid Imaging Reporting and Data System (TIRADS) of European Thyroid Association (EU), American College of Radiologists (ACR), and American Thyroid Association (ATA). A head and neck pathologist confirmed the diagnosis of NIFTP. Univariate analysis, multivariate logistic regression, and area under the receiver-operator-curve (AUC) are measured to determine the diagnostic performance of the distinguishing features.

Results: A total of 46 FTC including 8 oncocytic variants, 14 FVPTC, 10 NIFTP, and 34 FA are identified. The patients are predominantly female (77%), Chinese in ethnicity (63%) with a mean age of 47; 9.8% were hyperthyroid (TSH ≤ 0.45mIU/l). Comparing the benign vs the malignant FTTN, there is no statistically significant difference in cytologic category, with Bethesda III being predominant in all tumor types (53-72%). Neither is there a difference in age, sex, ethnicity, tumor size, nuclear atypia, individual sonographic features except for hypoechogenicity. Hyperthyroidism is more common in FA than other FTTN (20.7% vs. 3.8%, P = 0.05). Intermediate or high suspicion are associated with malignant FTTN in all 3 sonographic risk stratification systems (P < 0.01). Multivariate logistic regression of hyperthyroidism and EU-TIRADS, ACR-TIRADS, ATA, respectively, shows that the AUC of distinguishing benign from malignant FTTN differs only slightly (0.74-0.75 for radiologist A, 0.80-0.81 for radiologist B).

Conclusions: EU-TIRADS, ACR-TIRADS, or ATA perform equally well in differentiating malignant from benign FTTN. Hyperthyroidism further improves the diagnosis of FA. However, Bethesda III cytology can be common. Molecular testing and continual improvement in feature identification are needed to avoid diagnostic surgery.