Prevalence and prediction of malignancy in cytologically indeterminate thyroid nodules

Controversy surrounds the evaluation of nodules with indeterminate cytology results. Malignancy rates in these nodules are not low. We examined the malignancy rates in nodules that showed follicular neoplasm or atypical cells on cytology and attempted to predict malignancy based on ultrasonographic features.

We retrospectively analysed 5 years' cytopathology results of fine-needle aspiration biopsy (FNAB) specimens of indeterminate follicular thyroid lesions prior to thyroidectomy. The prevalence of malignancy on final histology was determined. The sonographic features of the thyroid nodules with respect to size, echogenicity, echo structure, border shape and presence of calcification were analysed.

A total of 86 patients (15 men, 61 women; mean age 52.1 +/- 12.5 years) with indeterminate cytology underwent thyroidectomy and had histopathological diagnoses. The average nodule was 18.9 +/- 12.3 mm. The prevalence of malignancy in patients with atypical cell cytology was 51.7% (30 of 59), and the prevalence of malignancy in patients with follicular neoplasm cytology was 15% (4 of 27). Malignancy prevalence was higher in patients who had follicular neoplasm cytology with atypical cells than in those without atypical cells (2 of 7 and 2 of 20, respectively). We found no significant correlations between sonographic or clinical features and malignancy in this patient group. Sonographic features and nodule size are not useful predictors of malignancy.

Until better molecular markers for malignancy are developed, surgical consultation remains necessary after examination of cytologically indeterminate FNAB specimens in patients with follicular thyroid lesions. But in follicular lesions without atypical cells the malignancy rate is low and reassessment later on could be an alternative approach.