Thyroid Nodule Sphericity Metrics Discriminate Benign and Malignant Follicular and Oncocytic Neoplasms

Background: We investigated if thyroid nodule taller-than-wide (TTW) feature and sphericity metrics are helpful in separating benign neoplastic thyroid nodules (follicular and oncocytic adenomas) from follicular thyroid carcinomas (FTC) and oncocytic thyroid carcinomas (OCA). Methods: This is a retrospective study of TTW sonographic feature as reported by radiologists and nodule sphericity metrics at two academic health systems. Surgical pathology reports for benign and malignant follicular and oncocytic neoplasms, non-neoplastic nodules (hyperplastic and adenomatoid), and classic papillary thyroid cancers (PTC) were extracted from enterprise data warehouses. We independently reviewed each ultrasound and recorded nodule dimensions to identify nodules that were TTW and determine if the proportion of TTW nodules is different in benign and malignant thyroid nodules of various histologies. We also evaluated the sphericity index and sphericity ratio, two quantitative measures of how close the 3D shape of the nodule is to a sphere. Results: In total, 1110 nodules were analyzed: 209 non-neoplastic nodules (hyperplastic and adenomatoid), 398 benign neoplasms (follicular and oncocytic adenomas), and 503 malignant neoplasms (FTC, OCA, PTC, and follicular variant-PTC [FV-PTC]) and noninvasive follicular thyroid neoplasm with papillary-like features (NIFTP). There was no statistical difference for the TTW feature when follicular and oncocytic adenomas were compared with FV-PTC, OCA, FTC, and NIFTP (χ2, p = 0.08, sensitivity of 28% [confidence interval 23-24%]), when follicular adenoma was compared with FTC (χ2, p = 0.64) or when oncocytic adenoma was compared with OCA (χ2, p = 0.08). Benign and malignant neoplasms were more likely than non-neoplastic nodules to be TTW (χ2, p = 0.02). In contrast, the sphericity index and sphericity ratio were significantly different in most comparisons of benign and malignant nodules (Wilcoxon, p < 0.03) except for oncocytic tumors. Conclusions: TTW shape has limited utility in distinguishing benign follicular and oncocytic neoplasms from malignancy. This sonographic feature was more common among all benign and malignant neoplasms when they were compared as a group to non-neoplastic nodules, which suggests this sonographic feature is an indicator of neoplastic growth (benign or malignant) but not cancer. Alternative methods, such as measures of sphericity, are needed to distinguish benign and malignant oncocytic and follicular neoplasms.