Oncocytic Follicular Neoplasm of the Thyroid: Clinical, Histological, and Ultrasound Characteristics of a Surgical Cohort

Background

Thyroid nodules with a cytological diagnosis of oncocytic follicular neoplasm (FN) are associated with a moderate risk of malignancy of approximately 30%. Management usually involves choosing between diagnostic surgery, typically hemithyroidectomy, and active surveillance. Identification of additional predictors of malignancy could contribute to more accurate risk assessment and personalized management.

Aim

To analyze the histological, clinical, and ultrasound characteristics of oncocytic follicular neoplasms and to assess their association with the risk of malignancy.

Materials And Methods

This observational study included a consecutive series of all surgically treated cases of oncocytic FN (diagnostic category IV according to the Bethesda System) at the Endocrinology Research Centre over a 2-year period (2021–2022). A retrospective review of medical records was performed to assess histological tumor types, patient age and sex, and ultrasound features of the nodules. According to the histological diagnosis, cases were divided into malignant, benign, and low-risk neoplasm groups to identify possible differences in clinical and ultrasound characteristics.

Results

The final cohort included 81 cases with oncocytic FN: 23 malignant lesions, 55 benign lesions, and 3 cases of noninvasive follicular thyroid neoplasm with papillary-like nuclear features. Oncocytic carcinoma was the most common malignant type (n=10), however, a substantial proportion of malignant cases were represented by other histological diagnoses, including classic and oncocytic subtypes of papillary thyroid carcinoma, as well as follicular thyroid carcinoma. Regional lymph node involvement was detected in only one case of papillary thyroid carcinoma. The risk of malignancy in the final cohort was 28.4% (95% CI 19.7–39.0) and was not associated with sex, age, nodule size, or solitary versus multinodular thyroid disease. No ultrasound feature differed significantly or showed a trend toward a difference between the benign and malignant groups. The distribution of EU-TIRADS categories also did not differ between the groups.

Conclusion

This study suggests the absence of reliable ultrasound and clinical predictors of malignancy risk in thyroid nodules with oncocytic FN cytological pattern. These findings indicate that other approaches to risk refinement are needed to guide the choice of optimal management for nodules with this cytological pattern.