PLT05 Cytomorphological Features for Fine Needle Aspiration of Thyroid Nodules Post Radioactive Iodine Treatment

This study investigates the cytomorphological and molecular characteristics of thyroid nodules in patients who underwent radioactive iodine (RAI) treatment for hyperthyroidism.

We analyzed thyroid fine needle aspiration (FNA) cases from RAI-treated patients from 2015-2024. Selected cytological slides were meticulously assessed by two board certified cytopathologists to evaluate the cytomorphological features of the nodules. Subsequently, the data derived from these cases were compared to that of general in-house thyroid FNA cases collected during 2022 and 2023. Furthermore, we compared the surgical resection outcomes between patients who had received RAI treatment and those who had not, in order to gain a comprehensive understanding of the impact of RAI treatment. 

Our study shows that thyroid nodules post RAI exhibit a higher rate of non-diagnostic and indeterminate nodules compared to the general population. This suggests that RAI treatment may cause atrophy and cytologic atypia in thyroid nodules, making it more challenging to make a definitive diagnosis. Therefore, careful examination and additional molecular studies are essential for the clinical management of these patients. Moreover, RAI is also a carcinogenic factor for thyroid malignancy, and our findings highlight the importance of close monitoring and follow-up of these patients to detect any potential malignancy early. Our study provides valuable insights into the cytomorphological and molecular features of thyroid nodules post RAI and can help guide clinical decision-making for the management of these patients. 

45 thyroid FNA reports from 24 patients, predominantly female, were reviewed. FNA biopsies occurred, on average, 16.9 years post-RAI treatment (Table 1). There is a higher malignancy rate in surgically resected nodules following RAI treatment (11/18, 61%) comparing to cases of Graves' disease that had not been treated with RAI (128/375, 34.1%, p=0.03, Table 1).
Additionally, thyroid nodules that developed post-RAI exhibited a significantly higher rate of Bethesda I (17.8%) and indeterminate nodules (28.9% for Bethesda III and 11.1% for Bethesda IV), than the general population (2.2% for Bethesda I, 9.1% for Bethesda III and 1.7% for Bethesda IV, p<0.01, Table 2).
On cytopathology, the thyroid nodules post RAI showed frequently exhibited oncocytic cells, anisonucleosis, nuclear enlargement, metachromatic stroma, and atrophic follicles (Table 3, Figure 1). Metachromatic stroma was more frequently present in indeterminate nodules (p<0.05, Table 3). 

FNA - Thyroid