Incidental Thyroid Nodule: OK, Now What?

Gordon H. Sun, MD, MS

Disclosures

December 13, 2016

Detecting Incidental Thyroid Nodules

According to the American Cancer Society, the incidence of thyroid cancer is increasing by over 5% annually in both US men and women, making this one of the fastest-growing cancers from an epidemiologic standpoint. Whether this is due to an actual rise in thyroid cancer cases or reflects improved diagnostic tools and closer surveillance remains controversial, although a growing body of evidence suggests the latter.[1,2,3] A national screening program for cancer, combined with a relatively low "add-on" cost for thyroid ultrasound, was believed to be a major driver in the 15-fold increase in thyroid cancer incidence, without change in mortality rates, from 1993 to 2011 in South Korea.[4]

Black and Welch[5] reported that advances in diagnostic imaging have permitted the ability to visualize increasingly smaller abnormalities, directly increasing disease prevalence. They also concluded that therapeutic effectiveness may be exaggerated by lead-time and length biases, in which earlier diagnosis may have no actual effect on the length of survival or may detect slowly progressing, non-clinically apparent disease. As Dr David Terris, Regents Professor of Otolaryngology and Endocrinology at Augusta University, stated in a phone interview, "We have to be careful about overdoing it. A little less ultrasound might not be so bad [since] follow-up has gotten so good."

Although a substantial proportion of new thyroid cancer diagnoses stem from nationally enacted programs such as Korea's, many other lesions are detected incidentally. An incidentally discovered thyroid nodule (ITN, or more colloquially, "thyroid incidentaloma") can be defined as a nodule not previously detected or suspected clinically, but identified through an imaging study in the course of investigating an unrelated condition. A 1955 study of 1000 consecutive individuals undergoing autopsy found that one half of the patients with no clinical history of thyroid disease had thyroid nodules.[6] Prevalence of ITNs varies by imaging modality: 1%-2% in PET, about 15% in CT and MRI of the neck, up to 25% in contrast-enhanced chest CT, and 67% in newer-generation ultrasound.[7,8]

In 2015, Hoang and colleagues[7] coauthored a white paper on behalf of the American College of Radiology to provide guidance on how to best manage ITNs detected during CT, MRI, or PET. Their approach was based on a three-tiered system developed at Duke University, in which further evaluation of ITNs should be considered in patients with high-risk imaging findings (eg, suspicious lymph nodes, local invasion, PET-avid nodule), those < 35 years of age with nodules ≥ 1 cm, and patients ≥ 35 years of age with nodules ≥ 1.5 cm.[9]

A single-institution case series of 107 patients undergoing fine-needle aspiration (FNA) of ITNs identified 21 of 60 (35%) patients whose ITNs were found on CT, MRI, or PET-CT and who would not have undergone FNA had the three-tiered system been implemented.[10] None of these 21 patients was later diagnosed with cancer.

The same group also published a larger retrospective study of 672 asymptomatic patients found to have cancer after undergoing thyroid surgery.[11] The study included 101 patients with ITNs, 64 of whom were identified using CT, MRI, or PET-CT and had available imaging. Eight patients with thyroid cancer would have been excluded from further diagnostic workup had the three-tiered system been utilized, representing 13% (8 of 64) of patients whose lesions were first seen on CT, MRI, or PET-CT and 1.2% (8 of 672) of all patients with thyroid cancers in the study cohort.

A third analysis applied the three-tiered system to the Surveillance, Epidemiology, and End Results cancer databases from January 1983 to December 2009, capturing 84,720 persons with thyroid cancer.[12] The 10-year relative survival rate and 10-year thyroid cancer-specific survival rate of patients who would have been excluded from diagnostic workup under the three-tiered system were 99.9% and 99.5%, respectively.

Case Continued: Is It Cancer?

The patient had no breathing, voice, or swallowing symptoms and no history of thyroid disease or radiation exposure to the neck. He had no immediate family members with thyroid disease. The patient did not demonstrate thyromegaly or neck masses on examination. Thyroid function testing was within normal limits.

Although the patient was given the option of surveillance ultrasound, he instead chose ultrasound-guided FNA of the thyroid nodules "just to be sure" and was referred to a pathologist. The 0.9-cm nodule sampling was interpreted as "follicular lesion of undetermined significance (FLUS)," whereas the 0.7-cm nodule was benign. The patient declined repeat FNA.

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