CLINICAL THYROIDOLOGY FOR PATIENTS
A publication of the American Thyroid Association
Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
Table of Contents
FNAB fine-needle aspiration biopsy
Sensitivity is the probability of a positive test among patients with disease
Specificity is the probability of a negative test among patients without disease
Positive Predictive Value (PPV) is the proportion of patients with positive test results who have tumor
Negative predictive value (NPV) is the proportion of patients with a negative test who do not have tumor
What is the study about? Preoperative neck ultrasound examination accurately identifies most malignant nodules in patients with fine-needle aspiration cytology results that are suspicious for malignancy
The full article title: “Role of ultrasound in thyroid nodules with a cytology reading of suspicious for papillary thyroid carcinoma.” It is in the April Issue of Thyroid (Volume 18 Issue 5 pages 517-22.) The authors are JY Kwak, EK Kim, MJ Kim, SW Hong, SH Choi, EJ Son, KK Oh, CS Park, WY Chung, and KW Kim. To view the abstract of this article see:
What is the problem being studied? Malignancy is found in up to 80% of FNAB cytology specimens interpreted as suspicious for papillary thyroid cancer. Current guidelines suggest that patients with this finding should undergo surgery but it is possible that neck ultrasound might identify the few patients with benign tumors, thus avoiding unnecessary surgery.
What was the aim of the study? To investigate the role of ultrasound in nodules with suspicious cytology on FNAB
Who was studied? 303 patients with 10,497 thyroid nodules who had neck ultrasound and FNAB
How was the study done? Ultrasound was performed by three radiologists with extensive thyroid ultrasound experience who also performed the ultrasoundguided- FNAB. Each nodule was determined to be either ultrasonographically consistent with malignancy or probably benign.
What were the results of the study? The diagnostic sensitivity of ultrasound in identifying malignant nodules was 96%, the specificity was 75%, the PPV was 95% and the NPV was 81%, and overall accuracy was 93%. (See Box)
How does this compare with other studies? A few studies report that about 80% of nodules yielding cytology that is suspicious for papillary thyroid carcinoma are found at surgery to be papillary thyroid cancers. Still, the studies are small and frequently mix several types of thyroid cancers, making the interpretation of the findings difficult. This study involved only ultrasound-guided FNAB after the ultrasound diagnosis had been established.
What are the Limitations of this study? The ultrasound examinations were done by three very experienced radiologists who performed the ultrasound-guided FNAB after the ultrasound diagnosis had been established, which may have played a role in increasing the accuracy of the cytology findings. A greater number of biopsies may have been done on nodules that appeared ultrasonographically malignant. An ultrasound examination done in the hands of less experienced ultrasonographers would yield less accurate information.
What are the implications of this study? The American Thyroid Association cancer guidelines advise either lobectomy or total thyroidectomy if a thyroid nodule yields cytology that is suspicious for papillary cancer. Even with excellent ultrasonographers, there is a small risk (~4%) of missing a diagnosis of thyroid cancer when the FNAB cytology is positive. One must know this risk when opting to forgo surgery when the cytology diagnosis is suspicious for papillary thyroid cancer and the ultrasound exam is negative.
To review the American Thyroid Association guidelines see: http://www.thyroid.org/professionals/publications/documents/Guidelinesthy2006.pdf