DOI: 10.1148/radiol.2473072233
(Radiology 2008;247:602-604.)
© RSNA, 2008
Thyroid Nodules: Is It Time to Turn Off the US Machines?1
John J. Cronan, MD
1 From the Department of Diagnostic Imaging, Rhode Island Hospital, the Warren Alpert Medical School of Brown University, 593 Eddy Street, Providence, RI 02903. Received December 31, 2007; final version accepted January 22, 2008.
Address correspondence to the author (e-mail: jcronan{at}lifespan.org).
Discuss this article online at www.rsna.org/radiology/discuss.
The authors of the article "Benign and Malignant Thyroid Nodules: US Differentiation—Multicenter Retrospective Study" in this issue of Radiology (1) present a well-organized multicenter study evaluating ultrasonographic (US) findings associated with benign and malignant thyroid nodules. I review one to two manuscripts a month from groups throughout the world, looking to establish more specific criteria and ultimately define histologic specificity in distinguishing benign from malignant nodules. These US series are all retrospective evaluations of thyroid nodules that emphasize the overlap between benign and malignant appearance, as well as the need to perform fine needle aspiration (FNA) if a precise diagnosis is the goal.
The degree of overlap in the US appearance of benign and malignant nodules is great enough that a cytologic FNA sample is usually necessary to make the diagnosis of a benign or malignant nodule. The Society of Radiologists in Ultrasound consensus panel acknowledged that, "[a]lthough there are certain trends in the US distinction of benign and malignant thyroid nodules, there is also overlap in their appearances. Because of the inconsistent predictive value of US features, most agree that FNA and cytopathologic evaluation of a thyroid nodule are usually required before a patient undergoes surgical resection for a possible thyroid malignancy" (2).
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WHY ASSESS THYROID NODULES?
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The article by Moon et al (1) continues the struggle to categorize nodules as benign or malignant with US criteria. Whether this will ever be sufficiently practical to avoid performing biopsy of certain nodules because they are clearly benign or malignant is still debatable. However, the article provokes a more important question that has percolated into the US and endocrinology worlds. Should we be searching for nonpalpable thyroid nodules with US and what are we accomplishing by doing so? What is the motivation? Because our technology permits detection of 2–3-mm nodules, should we maintain the chase? I fear we have accepted a sisyphean task in making all thyroid nodules a focus of concern. Is it time to reassess our goals in the detection and characterization of thyroid nodules?
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A NORMAL FINDING
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The prevalence of thyroid nodules in the U.S. population is dependent on the tool used for interrogation of the thyroid. With simple palpation, 4%–7% of the population has a thyroid nodule. At autopsy, 50%–60% of the population is found to have a thyroid nodule. However, the reservoir of clinically silent impalpable nodules is truly expanded when high-resolution US is utilized for thyroid evaluation. Up to 67% of the population evaluated with US will have an incidental thyroid nodule (3). Conservatively, if 50% of the U.S. population (approximately 300 million) has a nodule, we are dealing with a potential reservoir of 150 million Americans with a thyroid nodule. This pool of patients is only awaiting US interrogation in order to classify thyroid nodules requiring diagnostic assessment and categorization as benign or malignant.
Confirming the power of US, there has been a 2.4-fold increase in the reported incidence of thyroid nodules in the past 3 decades that is directly related to the use of US to search for thyroid nodules. Also contributing to this expanding pool of thyroid nodules is the incidental detection of nodules via computed tomography and magnetic resonance imaging (2). This increase in the detection of nodules has been accompanied by a three-fold increase in thyroid aspirates in the decade of 1995–2005 (4). A recent trend in the utilization of in-office US, often by endocrinologists, is accelerating the utilization of US in the general patient population and contributing to the detection of these nonpalpable nodules (5).
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MOST THYROID CANCERS ARE PAPILLARY
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Once a thyroid nodule is detected, the binary question remains, is it benign or malignant? Depending on the published series referenced, 6%–13% of thyroid nodules chosen for FNA will yield malignancy (2,6). Surprisingly, size is not a factor in determining the rate of malignancy. In fact, the incidence of thyroid cancer identified in nonpalpable thyroid nodules is the same as that identified in patients with palpable nodules (3).
The majority of thyroid cancers detected incidentally are papillary in origin. Unlike its malevolent associate anaplastic thyroid cancer, which while accounting for only 1%–2% of thyroid cancers is responsible for over half the cancer deaths, papillary thyroid cancer is very benign (7). The American Cancer Society estimated in 2005 that 25 690 new cancers of the thyroid were reported and 1460 individuals died of thyroid malignancy (8). Since papillary is the dominant thyroid cancer and is well differentiated, the prognosis is remarkably good, with a reported 30-year survival of 95% (8). With these facts in mind, despite the exponential increase in the detection of both nodules and thyroid malignancy, the incidence of thyroid deaths has been stable during the past 40 years. The entire increase in thyroid malignancy is secondary to papillary cancers and is related to the increased diagnostic scrutiny resulting in an apparent increase in incidence of thyroid cancer that is all papillary (5). This nonpalpable thyroid cancer has little biologic significance (9). In fact, in an autopsy series, Harach et al (10) opined that occult papillary cancer might well be a "normal" finding. Utilizing 2–3-mm sections of the thyroid in 101 autopsies, they located papillary cancer in 36% of people—all without any signs or symptoms during their life (10).
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HOW SMALL IS TOO SMALL?
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Left unchecked, this tsunami of thyroid nodules will overwhelm the health care system and have little beneficial outcome. Can we afford to locate and diagnose thyroid nodules in the 150–180 million Americans? With the dispersal of US units into the general medical community, the threshold for nodule evaluation is diminishing. Twenty years ago biopsy was performed only on palpable nodules—those larger than 2 cm. With US, we began to perform FNA for 1–2-cm nodules. Despite consensus articles by national organizations encouraging biopsy only for nodules that are larger than 1 cm, the opportunity to assess nonpalpable nodules smaller than 1 cm has been irresistible (2,9,11). We are now being asked to routinely perform FNA on 5–10-mm nodules because we can.
With every passing year, our US units are better, our biopsy techniques are improved, cytologic interpretation is refined, and we are essentially able to perform FNA on any lesion we can visualize. As Ross (4) pointed out to his endocrinology colleagues, we have an epidemic of thyroid nodules secondary to technology. There is no proof that our intervention on these nonpalpable nodules has any effect on improving the health and welfare of the population.
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THE FINANCES OF HUNTING FOR THYROID NODULES
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If we refuse to accept reality with regard to nonpalpable nodules, finances may well force us to reassess our direction. If we assume 150 million Americans have a thyroid nodule at US, and have a 10% rate of malignancy, we would need to perform biopsy on all and send at least 15 million to the operating room. The standard surgical treatment is a total thyroidectomy, often followed by radioactive iodine ablation (12). The financial costs, assuming biopsy and surgery at $20 000 for the 15 million with a diagnosis of papillary cancer, would conservatively reach 30 billion dollars. This does not include the costs of initial US evaluation, subsequent ablation treatments, follow-up monitoring, and pharmacologic replacement.
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OVERDIAGNOSIS: DO NO HARM
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From the patient perspective, we have hung the psychologic stigma of cancer on these patients, the dependency for daily thyroid supplementation, and the continual need for follow-up in the absence of any data suggesting what to do long term. We accept all these consequences to control a cancer with a 99% 10-year survival. As stated by Ross, "considering the anxiety, costs, and complications suffered by many of these patients, one can reasonably question the benefits of increased cancer detection" (4). These cancers would never have caused symptoms during life; increased diagnostic scrutiny is causing overdiagnosis (5). Our research focus should be the discovery of the small percentage of thyroid cancers that are aggressive and alter life spans.
Note that in this editorial, I am not addressing the palpable thyroid nodule or the nodule associated with metastatic disease. Rather, I am questioning the need to find subpalpable thyroid nodules; 87% of the increase in papillary thyroid malignancy are nodules smaller than 2 cm and 49% are smaller than 1 cm (5). Realizing the outcome of screening the thyroid, it well might be better to turn off the US machines. In summary, we need to develop an evidence-based strategy that will permit us to escape this flood of nodules.
Discuss this article online at www.rsna.org/radiology/discuss.
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FOOTNOTES
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Author stated no financial relationship to disclose.
See also the article by Moon et al in this issue.
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References
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- Moon WJ, Jung SL, Lee JH, et al. Benign and malignant thyroid nodules: US differentiation—multicenter retrospective study. Radiology 2008;247(3):762–770.
- Frates MC, Benson CB, Charboneau JW, et al. Management of thyroid nodules detected at US: Society of Radiologists in Ultrasound consensus conference statement. Radiology 2005;237(3):794–800.[Abstract/Free Full Text]
- Mazzaferri EL. Managing small thyroid cancers. JAMA 2006;295(18):2179–2182.[Free Full Text]
- Ross DS. Editorial: predicting thyroid malignancy. J Clin Endocrinol Metab 2006;91(11):4253–4255.[Free Full Text]
- Davies L, Welch HG. Increasing incidence of thyroid cancer in the United States, 1973–2002. JAMA 2006;295(18):2164–2167.[Abstract/Free Full Text]
- Iannuccilli JD, Cronan JJ, Monchik JM. Risk for malignancy of thyroid nodules as assessed by sonographic criteria. J Ultrasound Med 2004;23(11):1455–1464.[Abstract/Free Full Text]
- McIver B, Hay ID, Giuffrida DF, et al. Anaplastic thyroid carcinoma: a 50-year experience at a single institution. Surgery 2001;130(6):1028–1034.[CrossRef][Medline]
- Jemal A, Murray T, Ward E, et al. Cancer statistics, 2005. CA Cancer J Clin 2005;55(1):10–30. [Published correction appears in CA Cancer J Clin 2005;55(4):259.]
- Ross DS. Nonpalpable thyroid nodules: managing an epidemic. J Clin Endocrinol Metab 2002;87(5):1938–1940.[Free Full Text]
- Harach HR, Franssila KO, Wasenius VM. Occult papillary carcinoma of the thyroid: a "normal" finding in Finland—a systemic autopsy study. Cancer 1985;56(3):531–538.[CrossRef][Medline]
- Cooper DS, Doherty GM, Haugen BR, et al. Management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid 2006;16(2):109–141.[Medline]
- Shaha AR, Tuttle RM, Shah JP. Papillary microcarcinoma of the thyroid. J Surg Oncol 2007;95(7):532–533.[CrossRef][Medline]
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Benign and Malignant Thyroid Nodules: US Differentiation—Multicenter Retrospective Study
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[Abstract]
[Full Text]
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WHY ASSESS THYROID NODULES?
A NORMAL FINDING
