Thyroid nodules are diagnosed more often incidentally on radiologic exams, such as CT scans of the chest, MRI scans, PET scans and ultrasounds of the carotid arteries in the neck.
There is a conundrum of what to do with a thyroid nodule, especially when it is found incidentally. It depends on the size. If it is over one centimeter, usually it is biopsied by fine needle aspiration (FNA).
While most are asymptomatic, if there are symptoms, these might include difficulty swallowing, difficulty breathing, hoarseness, pain in the lower portion of the neck and a goiter.
FNA biopsy is becoming more common. There was a greater than 100 percent increase in thyroid FNAs performed from 2006 to 2011. This resulted in a 31 percent increase in thyroidectomies, surgeries to remove the thyroid, either partially or completely.
However, the number of thyroid cancers diagnosed with the surgery did not rise in this same period. In addition, the mortality rate has remained relatively stable over several decades at about 1,500 patients per year.
Thyroid nodules are least likely to be cancerous when the initial diagnosis is by incidental radiologic exam.
Treating borderline results
As much as 25 percent of FNA biopsies are indeterminate. We are going to look at two modalities to differentiate between benign and malignant thyroid nodules when FNA results are equivocal: a PET scan and a molecular genetics test.
A meta-analysis of PET scan results showed that it was least effective in resolving an unclear FNA biopsy. The PET scan was able to rule out patients who did not have malignancies but did not do a good job of identifying those who did have cancer.
On the other hand, a molecular-based test was able to potentially determine whether an indeterminate thyroid nodule by FNA was malignant or benign. In a study, researchers were able to not only rule out the majority of malignancies but also to rule them in.
It was not perfect, but 94 percent were ruled out and 74 percent were ruled in. The combination test improved the predictive results of previous molecular tests by 65 to 69 percent. This is important to help decide whether or not a patient needs surgery to remove at least part of the thyroid.
Significance of calcification on ultrasound
Microcalcifications in the nodule can be detected on ultrasound. Patients with microcalcifications are more likely to have malignant thyroid nodules than those without them, according to a small study involving 170 patients.
This does not mean necessarily that a patient has malignancy with calcifications, but there is a higher risk.
As I mentioned above, most thyroid nodules are benign. The results of one study go even further, showing that most asymptomatic benign nodules do not progress in size significantly after five years.
The factors that did contribute to growth of about 11 percent of the nodules were age (people under 45 years old had more growth than those over 60 years old), multiple nodules and greater nodule volume at baseline. Men were also at greater risk.
The authors’ suggestion is that, after the follow-up scan, the next ultrasound scan might be five years later instead of three years. However, they did discover thyroid cancer in 0.3 percent after five years.
Thyroid function may contribute to risk
In considering risk factors, it’s important to note that those who had a normal thyroid stimulating hormone (TSH) were less likely to have a malignant thyroid nodule than those who had a high TSH, implying hypothyroidism.
There was an almost 30 percent prevalence of cancer in the nodule if the TSH was greater than 5.5 mU/L.
The bottom line is, fortunately, most nodules are benign and asymptomatic. Still, it’s important to be checked if you have symptoms or if you have nodules discovered incidentally.