Proposed ATA Guidelines’ Sonographic Patterns Performance for MTC

NASHVILLE, Tenn. — The new sonographic patterns proposed in the provisional 2014 American Thyroid Association (ATA) guidelines perform well for medullary thyroid cancer (MTC), and interobserver agreement appears to be good overall, according to a new retrospective study presented at the American Association of Clinical Endocrinologists (AACE) 24th Annual Scientific & Clinical Congress. 

At the meeting, the researchers reported that most MTCs have an “intermediate” or “high-suspicion” sonographic pattern and therefore are unlikely to be missed by the new classification.

“It is reassuring to us. It does predict it in the same way, and we think it is important to look at this. We don’t want to miss something,” said study investigator Bryan McIver, MD, who is in the division of endocrine oncology at the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Florida. 

The development of the 2014 provisional ATA guidelines for the management of thyroid nodules was based on the appearance of papillary and follicular thyroid carcinoma. The guidelines provide a specific classification based on the sonographic pattern, and each specific pattern can be associated with an estimated risk for malignancy and ultimately determining a threshold for biopsy. However, the performance of the 2014 provisional ATA guidelines in MTC has been unclear.

McIver and his colleagues evaluated how MTC would be classified by the proposed system, and they also analyzed the agreement between different observers. The analysis included all patients with MTC seen at a single institution between 1998 and 2014. 

For this investigation, five independent reviewers with expertise in ultrasound — four endocrinologists and one radiologist — reviewed the images and each investigator assessed information regarding echogenicity, margins and calcifications. Each investigator also assessed extrathyroidal extension and presence of suspicious lymph nodes.

The researchers considered the shape “taller than wider” in the transverse view to be positive when there was a difference of at least 2 mm in the measurements given to identify the nodule, and this was common to all observers.  

Hetero-echogenic nodules in the absence of other suspicious features were considered “low-suspicion,” and iso-echogenic, hyper-echogenic or hetero-echogenic nodules with at least one suspicious feature were considered “high-suspicion.” The suspicion pattern was specified by the ATA classification and was followed in each situation. 

In 30 MTC cases, 90% to 100% were classified as “intermediate” or “high-suspicion” by all raters. The overall agreement for all categories was 77% with a Kappa coefficient of 0.72, according to the data. 

Although there was overall good agreement, the researchers found the agreement was moderate for the individual features, with the Kappa coefficient ranging from 0.44 for irregular margins to 0.56 for extrathyroidal extension and for presence of suspicious lymph nodes.

In this analysis, six of the 30 nodules evaluated were classified as “low-suspicion” by at least one of the observers. The researchers found that biopsy could have been delayed in one nodule, but a biopsy was warranted in five of the six due to size greater than 1.5 cm or clinical history.  

“This is a different type of cancer than follicular and papillary. We wanted to know if it applied to medullary. If you miss this, it can become an incurable cancer. We didn’t want to be at risk where we were missing a medullary cancer and miss the chance to cure it,” McIver said in an interview with Endocrinology Advisor.

“We need lots more studies in this area and studies done at multiple sites because how one person interprets a person’s ultrasound may be different from how another person interprets an ultrasound. We don’t know what is happening across the country as a whole,” said McIver.

Reference

1. Valderrabano P et al. Abstract #1004. Presented at: American Association of Clinical Endocrinologists (AACE) 24th Annual Scientific & Clinical Congress; May 13-17, 2015; Nashville, Tenn.