Natural history of benign solid and cystic thyroid nodules

Thyroid nodules are common and most often benign. The natural history of benign thyroid nodules, however, is unclear.

To determine the natural history of cytologically benign thyroid nodules using ultrasonography.

Retrospective case series.

Single tertiary care clinic.

All patients referred to the Brigham and Women's Hospital Thyroid Nodule Clinic, Boston, Massachusetts, who had benign cytologic results on ultrasonography-guided fine-needle aspiration of a thyroid nodule between 1995 and 2000 and returned for a requested follow-up examination 1 month to 5 years later.

Nodule dimensions were measured at both visits, and growth was defined as an increase in calculated volume of 15% or greater. These results were correlated with the time between examinations, age, sex, baseline serum thyroid-stimulating hormone concentration, and cystic content of each nodule.

Nodule volume increased over time (P < 0.001). The estimated proportion of nodules with an increase in volume of 15% or greater after 5 years was 89%. Nodules with greater cystic content were less likely to grow than solid nodules (P = 0.01). Seventy-four of the 330 nodules were reaspirated on the second visit. Despite an average increase in volume of 69%, only 1 of 74 reaspirated nodules was malignant.

Most solid, benign thyroid nodules grow. Therefore, an increase in nodule volume alone is not a reliable predictor of malignancy.