Thyroid nodule shape independently predicts risk of malignan
Predictive models of thyroid nodule cancer risk are presently based upon nodule composition, echogenicity, margins, and the presence of micro-calcifications. Nodule shape has shown promise to be an additive factor helping determine the need for nodule biopsy.

A prospective cohort study, patients with 1 or 2 clinically relevant thyroid nodules (predominantly solid and over 1 cm) presenting for diagnostic evaluation. The long-to-short nodule ratio was significantly lower in malignant compared to benign nodules indicating greater risk of malignancy in more spherical nodules [1.63±0.38 for malignant nodules vs 1.74±0.47 for benign, p<0.0001]. The risk of malignancy continually increased as the long-to-short ratio approached a purely spherical ratio of 1.0 [ratio >2.00, 14.6% cancer; ratio 1.51-2.00, 19.7%; ratio 1.00-1.50, 25.5%, p<0.0001]. In multiple regression analysis, younger age, male sex, and nodule's spherical shape were each independently associated with cancer risk.

The more a thyroid nodule is spherically shaped, as indicated by a long-to-short ratio approaching 1.0, the greater its risk of malignancy. This was independent of age, sex and nodule size. Incorporating a nodule’s sphericity in the risk stratification systems may improve individualized clinical decision-making.