CHICAGO — The two most important things to gather from an ultrasound study of thyroid nodules is the solidity and the presence or absence of calcifications, according to one expert.
These characteristics, not size, should guide a physician's decision about whether to perform a fine-needle aspiration to check for cancer, said Mary C. Frates, M.D., of Brigham and Women's Hospital in Boston.
“There is a misconception that larger size and the presence of a solitary rather than multiple nodules are predictors of malignancy, but this is not true,” she told this newspaper.
Speaking at the annual meeting of the Radiological Society of North America, Dr. Frates outlined her prospective study looking at the likelihood of malignancy based on ultrasound characteristics of more than 1,000 thyroid nodules.
All nodules had a diameter of at least 10 mm and were assessed on ultrasound, followed by ultrasound-guided fine-needle aspiration, as well as surgery when necessary.
The study found a malignancy rate of 11%, confirmed by pathology or cytology, among the 1,060 nodules.
The ultrasound characteristics measured included size, solidity, echogenicity, presence or absence of a halo, margins, presence or absence of calcifications, and whether there were single or multiple nodules.
Imaging indicated that the main differences between malignant and benign nodules lay in their solidity and calcifications.
Nodules that were at least 75% cystic had a low malignancy rate of almost 2%, compared with nodules that were at least 75% solid, which had a malignancy rate of 13%.
The presence of calcifications also was a strong predictor of malignancy. Fine punctate calcifications had the highest malignancy rate, at almost 24%, followed by calcifications on the rim only (17%), and coarse calcifications (16%). Nodules with no calcifications had a malignancy rate of 8%.
When the sonographic characteristics were combined, solitary nodules that were mostly cystic and without calcifications had a very low malignancy rate (2%), whereas solitary, mostly solid nodules with calcifications had a high malignancy rate (34%).
The same trend was seen in nonsolitary nodules. Those that were mostly cystic and without calcifications had a malignancy rate of 1%, while those that were mostly solid with calcifications had a malignancy rate of 19%.
Dr. Frates said ultrasound reports that do not include details about a nodule's solidity and calcifications offer little information regarding its malignancy potential. However, she says the ultrasound information must be considered along with the patient's history.
“The clinical evaluation of the patient is also critical,” she told this newspaper. “There are clinical characteristics that determine which patients are at increased risk for thyroid cancer—patients with a family history, patients with enlarged lymph nodes or hard masses, and patients who were radiated as children,” she said. “You have to consider the clinical history and the imaging findings together.”
Although large size should not influence a physician's decision to aspirate a nodule, Dr. Frates added that small size, under 10 mm, does influence her against a biopsy. And she cautioned physicians against doing unnecessary biopsies.
“By doing unnecessary biopsies, you increase your risk of getting insufficient cells. When you get two or three results that are insufficient, most institutions recommend performing a thyroidectomy because a small percentage of nodules that are persistently nondiagnostic turn out to be cancer,” she explained.
The appropriate management of thyroid nodules remains controversial because thyroid cancer is such a slow-growing disease and is not often fatal, she said.