Classical and Follicular Variant Papillary Thyroid Carcinoma: Comparison of Clinical, Ultrasonographical, Cytological, and Histopathological Features in 444 Patients

Follicular variant papillary thyroid carcinoma (FVPTC) is the most common variant of papillary thyroid carcinoma (PTC) after classical PTC (CPTC). In this study, we aimed to compare functional status, ultrasonographical features, cytological results, and histopathological characteristics of patients with CPTC and FVPTC. Preoperative thyroid functions, thyroid autoantibodies, ultrasonographical features, cytology, and histopathology results of 354 (79.9%) CPTC and 90 (20.3%) FVPTC patients were reviewed retrospectively. Sex distribution, mean age, thyroid autoantibody positivity, and thyroid dysfunctions were similar in two groups. Among 320 patients with preoperative ultrasonography (US) findings, a hypoechoic halo was observed more frequently (p = 0.003), and marginal irregularity was observed less commonly (p = 0.024) in FVPTC lesions. In CPTC, rate of malignant cytology (p = 0.001), and in FVPTC, rate of suspicious cytology (p < 0.001) were significantly higher. Histopathologically, mean tumor diameter was markedly higher in FVPTC compared to CPTC (16.89 ± 13.86 vs 10.64 ± 9.70 mm, p < 0.001), while capsular invasion and extrathyroidal spread were significantly lower in patients with FVPTC (p = 0.018 and p = 0.039, respectively). FVPTC tend to have more benign features in US and less malignant results in cytology. Higher tumor size in FVPTC might be explained by the recognition of clinical importance of these lesions after reaching particular sizes due to benign US features.