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Letters Reply to “Three-Tiered System for Incidental Thyroid Nodules: Do Not Forget the Calcifications” We thank Lacout et al. [1] for their interest in our article [2] and sharing their experience of additional findings on imaging that help to predict malignancy. Their comments were regarding PET metabolic uptake, thyroid calcifications, the Thyroid Imaging Reporting and Data System (TIRADS), and diffusion-weighted imaging. We agree with their comment that increased metabolic activity on PET should lead to further workup. For this reason 18F-FDG uptake in a thyroid nodule of any size meets the criteria of the three-tiered system. We appreciate their description of two anecdotal cases in which there was an absence of metabolic activity on PET in some histologic types of thyroid malignancy. Lacout et al. [1] also stated that calcifications on CT should be a finding that warrants workup. When we developed the three-tiered system, we considered morphologic features of thyroid nodules but did not find any evidence to suggest that calcifications on CT were associated with malignancy in incidental thyroid nodules [3, 4]. A recent article found the malignant rate to be higher in calcified nodules on CT, but the cohort was a malignancy-rich population of patients undergoing CT before thyroid surgery [5]. The study did not include patients with incidental thyroid nodules, which was the patient population of our study and the ideal target group for the three-tiered system. A study by Shetty et al. [6] did evaluate CT findings in incidental thyroid nodules and found calcifications to be present in 12% of thyroid nodules and no significant correlation between punctate calcifications on CT and malignant or potentially malignant histology. Lacout et al. [1] submitted two imaging examples of calcifications on CT in malignant nodules. The second example would have met the three-tiered system criteria for workup on the basis of the nodule size and presence of metastatic lymph nodes. There are far more studies evaluating malignant findings in thyroid nodules on ultrasound than on CT [3, 7–9]. These studies can provide insight into calcifications on CT, which correspond most closely to coarse calcifications on ultrasound. A large populationbased case-control study by Smith-Bindman et al. [7] that evaluated sonographic signs of
thyroid nodules found that there was a small association of coarse calcifications with malignancy in single-predictor modeling but no statistically significant association with multiple-predictor modeling. We agree that the presence of microcalcifications is a sensitive sign for malignancy, and thus it appears in the Society of Radiologists in Ultrasound (SRU) recommendations with a lower size threshold than a solid nodule without microcalcifications [7–9]. Unfortunately, microcalcifications are too small to be seen on CT. Lacout et al. [1] also propose the use of the TIRADS classification for thyroid nodules seen on ultrasound. We believe that such a system to standardize reporting is needed for thyroid nodules. However, to date, the American College of Radiology has not formally accepted the classification system. Thus, we did not apply the TIRADS classification to our cohort of thyroid nodules, but this could be a topic of future research. The final comment by Lacout et al. [1] was regarding the use of diffusion-weighted imaging to differentiate malignant from benign thyroid nodules on MRI. Several small studies have found lower apparent diffusion coefficient values in malignant thyroid nodules [2, 10], but these sequences are not obtained at all centers for neck MRI and are not part of the cervical spine MRI protocol. At our institution, we do not expect our technologists to review the MRI for incidental findings and add additional diffusion-weighted sequences. Given that this sign would be relatively rare, we did not include it in the three-tiered system. In conclusion, we acknowledge that neither the SRU recommendation nor the three-tiered system will be foolproof in diagnosing all cancers [11, 12]. The aim was not to diagnose all cancers but to diagnose cancers that have reached clinical significance while reducing workup in benign nodules. Our study showed that applying the SRU recommendations and the three-tiered system to incidental thyroid nodules can reduce incidental thyroid nodule workup by almost one third compared with current practice without specific guidelines. Jenny K. Hoang Duke University Medical Center, Durham, NC DOI:10.2214/AJR.14.12650 WEB—This is a web exclusive article.
References 1. Lacout A, El Hajjam M, Marcy PY. Three-tiered system for incidental thyroid nodules: do not forget the calcifications. (letter) AJR 2014; 203:[web] W451–W452 2. Hobbs HA, Bahl M, Nelson RC, et al. Incidental thyroid nodules detected at imaging: can diagnostic workup be reduced by use of the Society of Radiologists in Ultrasound recommendations and the three-tiered system? AJR 2014; 202:18–24 3. Hoang JK, Raduazo P, Yousem DM, Eastwood JD. What to do with incidental thyroid nodules on imaging? An approach for the radiologist. Semin Ultrasound CT MR 2012; 33:150–157 4. Nguyen XV, Choudhury KR, Eastwood JD, et al. Incidental thyroid nodules on CT: evaluation of 2 risk-categorization methods for work-up of nodules. AJNR 2013; 34:1812–1817 5. Wu CW, Dionigi G, Lee KW, et al. Calcifications in thyroid nodules identified on preoperative computed tomography: patterns and clinical significance. Surgery 2012; 151:464–470 6. Shetty SK, Maher MM, Hahn PF, Halpern EF, Aquino SL. Significance of incidental thyroid lesions detected on CT: correlation among CT, sonography, and pathology. AJR 2006; 187:1349–1356 7. Smith-Bindman R, Lebda P, Feldstein VA, et al. Risk of thyroid cancer based on thyroid ultrasound imaging characteristics: results of a population-based study. JAMA Intern Med 2013; 173:1788–1796 8. 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; 237:794–800 9. Frates MC, Benson CB, Doubilet PM, et al. Prevalence and distribution of carcinoma in patients with solitary and multiple thyroid nodules on sonography. J Clin Endocrinol Metab 2006; 91:3411–3417 10. Shi HF, Feng Q, Qiang JW, Li RK, Wang L, Yu JP. Utility of diffusion-weighted imaging in differentiating malignant from benign thyroid nodules with magnetic resonance imaging and pathologic correlation. J Comput Assist Tomogr 2013; 37:505–510 11. Erdem G, Erdem T, Muammer H, et al. Diffusionweighted images differentiate benign from malignant thyroid nodules. J Magn Reson Imaging 2010; 31:94–100 12. Bahl M, Sosa JA, Nelson RC, Hobbs H, Wnuk NM, Hoang JK. Incidental imaging-detected thyroid cancers in a ten-year period: how many cancers would be missed using the recommendations from the Society of Radiologists in Ultrasound? Radiology 2014; 271:888–894
AJR 2014; 203:W453 0361–803X/14/2034–W453 © American Roentgen Ray Society
AJR:203, October 2014 W453
Letters Reply to “Three-Tiered System for Incidental Thyroid Nodules: Do Not Forget the Calcifications” We thank Lacout et al. [1] for their interest in our article [2] and sharing their experience of additional findings on imaging that help to predict malignancy. Their comments were regarding PET metabolic uptake, thyroid calcifications, the Thyroid Imaging Reporting and Data System (TIRADS), and diffusion-weighted imaging. We agree with their comment that increased metabolic activity on PET should lead to further workup. For this reason 18F-FDG uptake in a thyroid nodule of any size meets the criteria of the three-tiered system. We appreciate their description of two anecdotal cases in which there was an absence of metabolic activity on PET in some histologic types of thyroid malignancy. Lacout et al. [1] also stated that calcifications on CT should be a finding that warrants workup. When we developed the three-tiered system, we considered morphologic features of thyroid nodules but did not find any evidence to suggest that calcifications on CT were associated with malignancy in incidental thyroid nodules [3, 4]. A recent article found the malignant rate to be higher in calcified nodules on CT, but the cohort was a malignancy-rich population of patients undergoing CT before thyroid surgery [5]. The study did not include patients with incidental thyroid nodules, which was the patient population of our study and the ideal target group for the three-tiered system. A study by Shetty et al. [6] did evaluate CT findings in incidental thyroid nodules and found calcifications to be present in 12% of thyroid nodules and no significant correlation between punctate calcifications on CT and malignant or potentially malignant histology. Lacout et al. [1] submitted two imaging examples of calcifications on CT in malignant nodules. The second example would have met the three-tiered system criteria for workup on the basis of the nodule size and presence of metastatic lymph nodes. There are far more studies evaluating malignant findings in thyroid nodules on ultrasound than on CT [3, 7–9]. These studies can provide insight into calcifications on CT, which correspond most closely to coarse calcifications on ultrasound. A large populationbased case-control study by Smith-Bindman et al. [7] that evaluated sonographic signs of
thyroid nodules found that there was a small association of coarse calcifications with malignancy in single-predictor modeling but no statistically significant association with multiple-predictor modeling. We agree that the presence of microcalcifications is a sensitive sign for malignancy, and thus it appears in the Society of Radiologists in Ultrasound (SRU) recommendations with a lower size threshold than a solid nodule without microcalcifications [7–9]. Unfortunately, microcalcifications are too small to be seen on CT. Lacout et al. [1] also propose the use of the TIRADS classification for thyroid nodules seen on ultrasound. We believe that such a system to standardize reporting is needed for thyroid nodules. However, to date, the American College of Radiology has not formally accepted the classification system. Thus, we did not apply the TIRADS classification to our cohort of thyroid nodules, but this could be a topic of future research. The final comment by Lacout et al. [1] was regarding the use of diffusion-weighted imaging to differentiate malignant from benign thyroid nodules on MRI. Several small studies have found lower apparent diffusion coefficient values in malignant thyroid nodules [2, 10], but these sequences are not obtained at all centers for neck MRI and are not part of the cervical spine MRI protocol. At our institution, we do not expect our technologists to review the MRI for incidental findings and add additional diffusion-weighted sequences. Given that this sign would be relatively rare, we did not include it in the three-tiered system. In conclusion, we acknowledge that neither the SRU recommendation nor the three-tiered system will be foolproof in diagnosing all cancers [11, 12]. The aim was not to diagnose all cancers but to diagnose cancers that have reached clinical significance while reducing workup in benign nodules. Our study showed that applying the SRU recommendations and the three-tiered system to incidental thyroid nodules can reduce incidental thyroid nodule workup by almost one third compared with current practice without specific guidelines. Jenny K. Hoang Duke University Medical Center, Durham, NC DOI:10.2214/AJR.14.12650 WEB—This is a web exclusive article.
References 1. Lacout A, El Hajjam M, Marcy PY. Three-tiered system for incidental thyroid nodules: do not forget the calcifications. (letter) AJR 2014; 203:[web] W451–W452 2. Hobbs HA, Bahl M, Nelson RC, et al. Incidental thyroid nodules detected at imaging: can diagnostic workup be reduced by use of the Society of Radiologists in Ultrasound recommendations and the three-tiered system? AJR 2014; 202:18–24 3. Hoang JK, Raduazo P, Yousem DM, Eastwood JD. What to do with incidental thyroid nodules on imaging? An approach for the radiologist. Semin Ultrasound CT MR 2012; 33:150–157 4. Nguyen XV, Choudhury KR, Eastwood JD, et al. Incidental thyroid nodules on CT: evaluation of 2 risk-categorization methods for work-up of nodules. AJNR 2013; 34:1812–1817 5. Wu CW, Dionigi G, Lee KW, et al. Calcifications in thyroid nodules identified on preoperative computed tomography: patterns and clinical significance. Surgery 2012; 151:464–470 6. Shetty SK, Maher MM, Hahn PF, Halpern EF, Aquino SL. Significance of incidental thyroid lesions detected on CT: correlation among CT, sonography, and pathology. AJR 2006; 187:1349–1356 7. Smith-Bindman R, Lebda P, Feldstein VA, et al. Risk of thyroid cancer based on thyroid ultrasound imaging characteristics: results of a population-based study. JAMA Intern Med 2013; 173:1788–1796 8. 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; 237:794–800 9. Frates MC, Benson CB, Doubilet PM, et al. Prevalence and distribution of carcinoma in patients with solitary and multiple thyroid nodules on sonography. J Clin Endocrinol Metab 2006; 91:3411–3417 10. Shi HF, Feng Q, Qiang JW, Li RK, Wang L, Yu JP. Utility of diffusion-weighted imaging in differentiating malignant from benign thyroid nodules with magnetic resonance imaging and pathologic correlation. J Comput Assist Tomogr 2013; 37:505–510 11. Erdem G, Erdem T, Muammer H, et al. Diffusionweighted images differentiate benign from malignant thyroid nodules. J Magn Reson Imaging 2010; 31:94–100 12. Bahl M, Sosa JA, Nelson RC, Hobbs H, Wnuk NM, Hoang JK. Incidental imaging-detected thyroid cancers in a ten-year period: how many cancers would be missed using the recommendations from the Society of Radiologists in Ultrasound? Radiology 2014; 271:888–894
AJR 2014; 203:W453 0361–803X/14/2034–W453 © American Roentgen Ray Society
AJR:203, October 2014 W453
