Assessment of malignancy rate in thyroid nodules according to the Bethesda system of fine-needle aspiration. Report from a tertiary center in the Southwestern region of Saudi Arabia.

Objective: To determine the rates of malignancy of thyroid nodules in each standard cytologic diagnostic category of the Bethesda system.

Methods: In a retrospective cohort study from October 1998 to April 2007 at the Department of Pathology, Aseer Central Hospital, Southwestern region of Saudi Arabia, all cases of thyroid nodules that underwent preoperative cytologic examination by fine-needle aspiration (FNA) and concurrent postoperative histopathologic examination were included. All FNA diagnoses were reclassified using the thyroid FNA Bethesda reporting system, including non-diagnostic (insufficient), benign, atypical follicular lesion of undetermined significance (AFLUS), neoplasm, suspicious of malignancy, and malignant groups. The rate of malignancy based on final histopathologic evaluation was analyzed for each of these cytologic groups.

Results: A total of 323 thyroid fine needle aspiration cytology (FNAC) diagnoses were reclassified into non-diagnostic 6.2%, benign 57.3%, AFLUS 13.6%, follicular and Hurthle cell neoplasms 16.1%, suspicious of malignancy 1.5%, and malignant 5.3% groups. The corresponding rate of malignancy on histopathologic examination was as follows: 35% in the non-diagnostic group, 10.3% in the benign group, 15.9% in AFLUS group, 32.7% in follicular and Hurthle cell neoplasms, 60% in the suspicious of malignancy group, and 94% in the malignant group.

Conclusion: Applying a standard terminology reporting system for thyroid FNA may enhance the communication between pathologists and clinicians, assists them to find out the rate of malignancy in each cytologic group, and facilitating a more consistent approach for patients' management.