Sonographic Features of the Follicular Variant of Papillary Thyroid Carcinoma

Abstract

The purpose of this study was to evaluate the sonographic findings of the follicular variant of papillary thyroid carcinoma (FVPTC) and to assess the role of preoperative fine-needle aspiration biopsy (FNAB). The sonographic findings of 27 thyroid nodules in 26 patients (2 male and 24 female; mean age, 45 years) with surgically proven FVPTC were reviewed retrospectively. Findings were categorized according to the echogenicity, margin, shape, and presence of microcalcifications. Malignant findings included marked hypoechogenicity, irregular or microlobulated margins, a taller-than-wide shape, and microcalcifications. Thyroid nodules with a single malignant finding as described above were classified as malignant. All patients underwent sonographically guided FNAB, and the sensitivity of the cytologic results was calculated. Lesion sizes varied from 3 to 34 mm (mean, 15.2 mm), and lesions were most commonly solid (23 [85.2%]), hypoechoic (14 [51.9%]), and oval (17 [63%]) with well-defined margins (14 [51.9%]) and no microcalcifications (23 [85.2%]). Eighteen lesions (66.7%) were correctly classified as malignant, whereas 9 (33.3%) were classified as benign on the basis of sonographic criteria. Twenty-four samples were adequate for cytologic examination, and 3 were inadequate. Twenty-one of 24 diagnostic cytologic results (87.5%) were suspicious for papillary carcinoma (5 of 21 [20.8%]) or malignant (16 of 21 [66.7%]), whereas 3 lesions (12.5%) had benign results. The sensitivity of FNAB was 77.8% (21 of 27). The follicular variant of papillary thyroid carcinoma tends to have relatively benign sonographic features, such as hypoechogenicity, well-defined margins, an oval shape, and no microcalcifications, but most lesions were correctly classified as malignant by both sonography and FNAB. The possibility of FVPTC should be considered when thyroid nodules with a relatively benign sonographic appearance have suspicious or malignant FNAB results.