Radiology: Ultrasound-based risk score predicts thyroid malignancy

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US scan shows irregular margin indicative of malignancy. Source: Radiology.

A relatively simple and practical thyroid imaging reporting and data system (TIRADS) based on the number of suspicious ultrasound (US) features can be applied to risk stratify thyroid nodules, according to a study published in the September issue of Radiology.

Widespread use of ultrasound has resulted in an increase in the detection of thyroid nodules. However, less than 10 percent of these nodules are malignant.

Deciding which patients should undergo fine needle aspiration biopsy (FNAB) presents a diagnostic dilemma as the same nodule may be classified differently using different guidelines. “Appropriate criteria are necessary to avoid an increase of rather unnecessary benign cytologic results in thyroid nodules,” wrote Jin Young Kwak, MD, from the department of radiology, research institute of radiological science at Yonsei University of College of Medicine in Seoul, South Korea.

Previous TIRADS have been complex and difficult to apply in practice, according to the researchers. Thus, they sought to develop a practical TIRADS to stratify malignancy risk and devised a retrospective study of 1,658 thyroid nodules which were biopsied via ultrasound guidance from May 2008 to December 2008. The study population included 1,373 women and 265 men.

Seven radiologists performed real-time ultrasound on the patients and categorized nodules according to the internal component, echogenicity, margins, evidence of calcifications and shape. Following the ultrasound study, the same radiologists performed US-guided FNAB. Results were analyzed and compared according to sex and ultrasound features.

Kwak and colleagues reported 275 malignant nodules. Benign nodules were significantly larger than malignant nodules (mean size, 20.7 mm vs. 15.5 mm, respectively), and patients with benign nodules tended to be older.

According to the univariate analysis, several ultrasound features demonstrated a significant association with malignancy. These were: solid component, hypoechogenicity, marked hypoechogenicity, microlobulated or irregular margins, microcalcification and taller-than-wide shape.

The risk and probability of malignancy increased as the number of suspicious features increased, the researchers said.

The authors used the findings to create TIRADS categories, which were defined as:

  • Category 3—no suspicious features;
  • Category 4a—one suspicious feature;
  • Category 4b—two suspicious features;
  • Category 4c—three or four suspicious features;
  • Category 5—five suspicious features.

The authors acknowledged a few shortcomings to the study. Namely, only a subset of the population was followed, the study was single-site design and limited to nodules that underwent FNAB, researchers did not account for false-negative and false-positive cytologic results and the malignancy probabilities have a fairly wide range. The researchers did not examine cost-effectiveness of the approach. Finally, although TIRADS risk of malignancy is similar to BI-RADS categories, the clinical aggressiveness and prevalence of the two nodule types differs.

Despite these issues, the researchers emphasized the practical utility of the risk score. “This new TIRADS can be easily applied in the clinical field because it is not difficult for those who perform US to count the number of suspicious US features,” wrote Kwak.