Determination of the optimal time interval for repeat evaluation after a benign thyroid nodule aspiration

Abstract

Introduction: The optimal timing for repeat evaluation of a cytologically benign thyroid nodule greater than 1 cm is uncertain. Arguably, the most important determinant is the disease-specific mortality resulting from an undetected thyroid cancer. Presently there exist no data that evaluate this important end point.

Methods: We studied the long-term status of all patients evaluated in our thyroid nodule clinic between 1995 and 2003 with initially benign fine-needle aspiration (FNA) cytology. The follow-up interval was defined from the time of the initial benign FNA to any one of the following factors: thyroidectomy, death, or the most recent clinic visit documented anywhere in our health care system. We sought to determine the optimal timing for repeat assessment based on the identification of falsely benign malignancy and, most important, disease-related mortality due to a missed diagnosis.

Results: One thousand three hundred sixty-nine patients with 2010 cytologically benign nodules were followed up for an average of 8.5 years (range 0.25-18 y). Thirty deaths were documented, although zero were attributed to thyroid cancer. Eighteen false-negative thyroid malignancies were identified and removed at a mean 4.5 years (range 0.3-10 y) after the initial benign aspiration. None had distant metastasis, and all are alive presently at an average of 11 years after the initial falsely benign FNA. Separate analysis demonstrates that patients with initially benign nodules who subsequently sought thyroidectomy for compressive symptoms did so an average of 4.5 years later.

Conclusions: An initially benign FNA confers negligable mortality risk during long-term follow-up despite a low risk of identifying several such nodules as thyroid cancer. Because such malignancies appear adequately treated despite detection at a mean 4.5 years after falsely benign cytology, these data support a recommendation for repeat thyroid nodule evaluation 2-4 years after the initial benign FNA.

Figure 1.

Distribution of follow-up intervals (years) among 1369 patient with 2010 cytologically benign thyroid nodules. The mean duration of follow-up is 8.5 years.

Figure 2.

Subanalysis of the study cohort. Years of mortality-free follow-up are depicted and grouped by the variable defining the completion of patient follow-up. The bottom row depicts the mean follow-up of the 18 false-negative thyroid cancers.