Sonographic differences between conventional and follicular variant papillary thyroid carcinoma

Abstract

Follicular variant papillary thyroid carcinoma (FVPTC) may pose a diagnostic challenge due to higher likelihood of lower risk cytology compared to conventional papillary thyroid carcinoma (CPTC). Recent guidelines have recommended the use of sonographic features to guide decisions to biopsy thyroid nodules. The purpose of this study was to evaluate the sonographic features of CPTC and FVPTC. This is a retrospective study design done in an Academic teaching hospital setting. Preoperative ultrasounds of 79 patients with conventional CPTC (48) and FVPTC (31) were reviewed by a radiologist blinded to histological diagnosis. Sonographic features of nodules were classified according to the British Thyroid Association (BTA) U-classification system as normal (U1), benign (U2), indeterminate (U3), suspicious (U4), and malignant (U5). Pathology slides of patients with FVPTC were reviewed by two pathologists and subclassified into encapsulated, well circumscribed/partly encapsulated, and infiltrative subtypes. FVPTC had a significantly lower incidence of any calcifications (p = 0.0005), microcalcifications (p = 0.002), and irregular or lobulated margins (p = 0.03) than CPTC. Differences in hypoechogenicity (p = 0.06), taller > wide shape (p = 0.17) and presence of halo (p = 0.07) were not significant. FVPTC was significantly less likely to be classified sonographically as malignant (U5) (p = 0.006) or suspicious/malignant (U4/5) (p = 0.009) than conventional PTC. Among FVPTC cases, infiltrative FVPTC were more likely to be sonographically classified as suspicious/malignant (U4/5) than non-infiltrative FVPTC. FVPTC nodules are less likely to show sonographic features of malignancy than conventional PTC. Reliance solely on sonographic features for thyroid nodule evaluation may not be sufficient to exclude FVPTC.

Correlations between Molecular Landscape and Sonographic Image of Different Variants of Papillary Thyroid Carcinoma

“…Invasive encapsulated FV is typically a hypoechoic lesion with rather smooth margins and no calcifications. Nodule shape, orientation, and vascularity are similar to the infiltrative type of FV [31,39]. Similar observations concerning more benign US features of nodules harboring RAS mutations were presented by Rossi et al [25], who demonstrated that most of them were isoechoic.…”

“…BRAF K601E mutations are present in most cases of the infiltrative follicular variant (FV) [12]. In US, these nodules are often hypoechoic, with spiculated/microlobulated margins and microcalcifications [31,39]. The differences in the US pattern of FV PTC depending on genetic drivers are discussed further below.…”

“…Nodules are often ovoid to round in shape, with a non-parallel orientation and mixed vascularization. The presence of microcalcifications is less common in the FV than in the classic variant of PTC (41.2% vs. 17.6%) [31,39]. Invasive encapsulated FV is typically a hypoechoic lesion with rather smooth margins and no calcifications.…”

Diagnosis of Thyroid Nodules: Performance of a Deep Learning Convolutional Neural Network Model vs. Radiologists

“…This would be expected, as established suspicious US features are suggestive of this cancer type 2 . All of the misclassified cancers by radiologists were either FVPTC or minimally invasive follicular thyroid carcinoma, which tend to show more benign US features 29,30 . Although sCAD and dCAD showed a similar number of misclassified cancers, they differed in characteristics – conventional papillary thyroid carcinoma accounted for 72.7% (8 of 11) of the misclassified cancers by sCAD, whereas it accounted for only 33.3% (4 of 12) of the misclassified cancers by dCAD.…”

Molecular Aspects of Thyroid Calcification

“…This explains why the follicular variant of PTC (FVPTC) has a very low frequency of microcalcifications (PBs) [ 69 ]. When FVPTC is infiltrative, the frequency of calcification can be higher but is rare in the encapsulated FVPTC [ 56 , 57 ]. Diffuse sclerosing variant of papillary thyroid carcinoma (DSVPTC) is an uncommon variant of PTC, characterized by diffuse involvement of one or both lobes of the thyroid gland [ 70 ].…”