Indeterminate thyroid nodules (Thy3): malignancy rate and characteristics in a study of 118 patients

Thyroid nodules are common, and the combined use of ultrasound and fine needle aspiration cytology provides useful information on their malignancy risk. The Thy reporting system is widely used in the United Kingdom, with malignancy rates for Thy3 cytology being quoted between 5% and 30%. This study aims to establish the risk of thyroid cancer in operated patients with Thy3 cytology and correlate it with patient demographics and nodule size.

This is a retrospective observational study of all thyroidectomies that took place in a single institution over a 3-year period (2019-2022). Those with a preoperative cytology of Thy3 were analysed further and in particular, nodule size, final histology and patients' demographics were documented.

Some 260 thyroidectomies were performed during the study period. Of these, 118 patients had Thy3 cytology. In the Thy3a group (n = 70), the malignancy rate was 27.1%. The average age of those with thyroid cancer was 51.4 vs 51.2 years for those with benign disease. The nodule size was under 40mm for both groups (36mm vs 39.7mm). In the Thy3f group (n = 48), the malignancy rate was 43.8%. The average age of those with thyroid cancer was 53.5 vs 56.2 years for those with benign disease. The nodule size was similar (24.5mm vs 27.6mm).

In this study, one in three patients with Thy3 cytology was diagnosed with thyroid cancer. We urge local units to analyse their data, to aid patients' informed decision-making. Within the subgroups, there was no significant difference in average nodule size or patients' age.