Ultrasound useful for risk stratification after nondiagnostic thyroid biopsy

1. Among patients with a nondiagnostic fine needle aspiration biopsy (FNAB) of thyroid nodules, the use of an ultrasound-based evaluation tool appropriately stratified patients according to malignancy risk. 

2. Results suggest that thyroid nodules with two or more suspicious ultrasound features should undergo repeat FNAB, while those with fewer than two suspicious features can be followed with ultrasound. 

Evidence Rating Level: 3 (Average)        

Study Rundown: Evaluation of patients with thyroid nodules typically includes FNAB, an approach critical for the detection of cancer. Although the majority of biopsies are adequate for a cytological diagnosis, up to 21% will be nondiagnostic. These biopsies represent a significant problem, and the management of thyroid nodules in which FNAB is nondiagnostic remains controversial. This study examined the usefulness of repeat FNAB in detecting malignancy in nondiagnostic thyroid nodules in relation to the thyroid imaging reporting and data system (TIRADS), a classification scheme for malignancy risk based on abnormalities and suspicious features detected via ultrasound. Nondiagnostic thyroid nodules were evaluated retrospectively according to TIRADS, and malignancy risk was calculated for nodules in each TIRADS categories. Results of the investigation suggest that TIRADS can appropriately stratify patients according to their risk of thyroid malignancy. Based on this, the authors suggested that for nodules with fewer than two suspicious features can be followed with ultrasound, while those with two or more may benefit from repeat FNAB. This study is limited in its retrospective nature, which may have introduced selection bias when considering how nodules were categorized in the analysis. Additionally, the number of nodules across each TIRADS category varied, which may have impacted the significance of the findings.

Click to read the study in Radiology

Relevant Reading: Thyroid imaging reporting and data system for US features of nodules: a step in establishing better stratification of cancer risk

In-Depth [retrospective cohort]: The medical records of 530 patients (430 women, 100 men) with nondiagnostic thyroid FNABs were retrospectively reviewed, with a total cohort of 548 nodules (7.3% malignant, 92.7% benign). Malignancy risk for the nodules was stratified into TIRAD categories based on suspicious ultrasonography findings such as hyper- and hypo- echogenicity, atypical internal variation, calcifications, irregular margins and abnormal shape. The malignancy risks of categories 3 and 4a nodules were 0.8% and 1.8%, respectively, while malignancy risks for higher TIRADS categories of 4b, 4c, and 5 nodules were 6.1%, 14.4%, and 31%. Researchers in this study also classified nodules according to size (294 larger than 10mm, 254 10mm or smaller). Among nodules >10mm, the malignancy risks of categories 3, 4a, 4b, 4c, and 5 nodules were 0.9%, 1.3%, 0%, 15%, and 33%, respectively. Among nodules ≤10 mm, the malignancy risks of categories 3, 4a 4b, 4c, and 5 nodules were 0%, 2.7%, 14%, 14.3%, and 31%.

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