Reliability of fine-needle aspiration for thyroid nodules greater than or equal to 4 cm

Abstract

Background

Fine-needle aspiration (FNA) is considered the diagnostic test of choice in the evaluation of thyroid nodules. Some practice recommendations, however, suggest surgical resection of larger thyroid nodules due to concerns of FNA unreliability in the diagnosis of thyroid malignancy. The purpose of this study was to determine the reliability of FNA in thyroid nodules ≥4 cm.

Methods

Retrospective review of prospectively collected data of 1068 consecutive patients who underwent FNA and thyroidectomy at a single tertiary medical center from 2003 to 2010 was performed. Patients were divided into two groups: those patients with a dominant thyroid nodule ≥4 cm (n = 212) and those patients with a dominant thyroid nodule <4 cm (n = 856). Sensitivity, specificity, and negative and positive predictive values were calculated for FNA results and final histopathology after thyroidectomy.

Results

Of 212 patients with lesions ≥4 cm, 35% had thyroid malignancy on final pathology. Conversely, 54% of 856 patients with dominant thyroid nodules <4 cm had a final diagnosis of thyroid cancer after thyroidectomy. FNA demonstrated similar test characteristics among patients with lesions ≥4 cm and <4 cm, with a specificity of 99% (CI: 96%–100%) and 98% (CI: 96%–99.0%), respectively, and a sensitivity of 35% (CI: 23%–49%) and 42% (CI: 37%–46%), respectively. The positive predictive value of FNA was 82% (CI: 75%–100%) for nodules ≥4 cm and 96% (CI: 92%–98%) for nodules <4 cm. Negative predictive value was significantly different, with a value of 82% (CI: 75%–87%) for lesions ≥4 cm and only 59% (CI: 55%–63%) for lesions <4 cm.

Conclusions

The reliability of FNA as a diagnostic test is not affected by the size of thyroid nodules. Routine surgical resection for all thyroid nodules ≥4 cm should not be used as the only independent factor in determining need for surgical resection.

Introduction

Clinically palpable thyroid nodules are present in 4% to 7% of the adult population in the United States [1]. Furthermore, advanced diagnostic imaging has greatly increased the frequency of incidentally discovered thyroid nodules [1]. The clinical relevance of these nodules is related to the concern of underlying thyroid malignancy among patients and clinicians alike. The overall incidence of malignancy in a patient with thyroid nodules and no associated risk factors is 9% to 13% [1], [2]. The incidence of thyroid cancer has increased sharply since the mid-1990s due in part to the discovery of incidental nodules in more frequent imaging studies [3].

Fine-needle aspiration (FNA) is a principal diagnostic test in the evaluation of thyroid nodules [4]. FNA is highly sensitive and specific in the diagnosis of thyroid cancer, with an accuracy approaching 98% [1], [4]. The false-negative rate for benign FNA results is low, with reported rates between 1% and 5% [1]. Some studies, however, suggest routine surgical resection of larger thyroid nodules due to concerns of FNA unreliability in the diagnosis of thyroid malignancy.

There is conflicting evidence regarding the accuracy of FNA in the evaluation of large nodules for thyroid carcinoma. Some clinicians report a FNA false-negative rate as high as 30% in patients with large thyroid nodules [4]. Conversely, some authors report a false-negative rate of FNA in large nodules to be as low as 0.7% [5]. The purpose of this study, therefore, was to determine the reliability of FNA in the evaluation of thyroid nodules ≥4 cm.