Management of Nonpalpable Thyroid Nodules
ABSTRACT & COMMENTARY
Synopsis: Patients with nonpalpable thyroid nodules who have a family history of medullary thyroid cancer or radiation should receive an ultrasound-guided fine-needle aspiration. Without such a history, nodules less than 1.5 cm require only careful observation.
Source: Tan GH, Gharib H. Ann Intern Med 1997;126:226-231.
The prevalence of thyroid incidentalomas (otherwise known as nonpalpable thyroid nodule) is unknown. However, we do know that the general population has a prevalence of palpable thyroid nodules on the order of 4-7%. This percentage is higher in patients with risk factors, such as age, female gender, iodine deficiency, or exposure to external radiation. With the advent of sophisticated, highly sensitive imaging techniques, such as ultrasonography or scintigraphy of the thyroid, clinicians have discovered that thyroid incidentalomas occur in asymptomatic patients.
Physicians have long known that clinical exam of the thyroid is fraught with problems. No clear standards for examination exist, including where to stand (in front of or behind the patient), having them swallow, or what position the neck should be in. We only know that clinical palpation is not a precise tool for picking up nodules. It is the best we have on the history and physical.
Somewhere in the area of 30% of patients who die have thyroid nodules. It is unknown how many have been undetected or worked up, but I suspect few.
Ultrasonography of the thyroid has resulted in high resolution images that can pick up nodules not clinically palpable. Studies published using either ultrasonography or scintigraphy indicate that thyroid incidentalomas occur in both normal glands and in glands with palpable solitary nodules. These incidentalomas are often completely missed on clinical palpation. The prevalence of thyroid incidentalomas detected on ultrasonography varied from 17% to 67% based on the study.
What is the risk of malignancy with these incidentalomas? Although accurate data do not exist, we do know that papillary thyroid cancer has an excellent prognosis because of its long course and its response to treatment. Almost all the occult thyroid carcinomas are papillary; therefore, not surprisingly, most think missing them when they are smaller than 1 cm doesn’t truly affect morbidity and mortality. Less than 1% of benign nodules increase in size during follow-up, and one can be assured that most benign nodules remain benign.
An excellent algorithm included in the article succinctly and efficiently tells us what to do with thyroid incidentalomas. After asking for a family history of thyroid cancer or history of childhood neck or head radiation or medullary cancer, those with positive responses need ultrasound-guided fine-needle aspiration (FNA). If the answers are negative, the ultrasound size less than 1.5 cm should reassure the clinician, and they should observe in a careful fashion over time. If the nodule is greater than 1.5 cm, it should be suspected to be malignant and then possibly undergo an ultrasound-guided FNA. They do not suggest thyroid suppression therapy and remind us that we do not need to immediately treat most non-palpable nodules found on the ultrasonographic and scintigraphic methods now available.
COMMENT BY LEN SCARPINATO, DO
As an active clinician, I’ve often wondered what to do about thyroid nodules that I palpate. So, you can imagine how confused I am by the ones I can’t feel but am told about by ultrasound or scintigraphic imaging. With the development of these very sensitive ways to pick up nonpalpable nodules, it is not surprising that clinicians would become confused on how to take care of them. Tan and Gharib give us a viable algorithm for the approach of these patients. They reassure us that nodules smaller than 1.5 cm can be followed. Those larger than that follow the usual scenario of fine-needle aspiration, which we are generally accustomed to doing with palpable thyroid nodules or with patients who have any risk factor.
The hidden caveat of this article is close and accurate follow-up. Patients need to be assessed for the potential of malignancy, which is low (< 1%) but real. Also, at no point do the authors address the issue of a thyroid function study, which is traditionally ordered when nodules are found palpably. The studies are probably being ordered when nodules are found on an ultrasound or scintigraphy. You probably need them even less in that scenario.