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Letters Three-Tiered System for Incidental Thyroid Nodules: Do Not Forget the Calcifications We read with great interest the article by Hobbs et al. [1], “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?” in the January 2014 issue of the AJR. The authors emphasize that using the Society of Radiologists in Ultrasound recommendations with the three-tiered system may reduce the workup of incidental thyroid nodules by one third compared with current practice without specific guidelines. In our experience, some benign thyroid nodules (oncocytomas) display significant 18F-FDG PET uptake, whereas some papillary carcinomas show no uptake, probably owing to their strong stromal fibrous reaction. Excessive host desmoplastic reaction, in limiting tumor growth, may decrease both tumor feeding vascularization and FDG uptake. Thus, the absence of FDG uptake should not definitively exclude malignancy. However, we agree with Hobbs et al. [1] that PET uptake should indicate prompt ultrasound characterization, especially because this finding indicates a tumor presenting with aggressive biologic behavior [2]. With regard to the three-tiered system, we think that some important items are lacking. Indeed, the presence of calcifications incidentally detected on CT may evoke the diagnosis of thyroid papillary or medullar malignancies because both tumors harbor calcifications (Figs. 1 and 2). Those CT features should eventually lead to further ultrasound characterization to distinguish benign calcifications from malignant microcalcifications. Indeed, the detection of microcalcifications

is clinically relevant because their presence (psammoma bodies) may be a sign of thyroid papillary malignancy of worse prognosis [3]. Although rare, calcifications may be involved in the mechanism of amyloidosis deposition, classically reported in medullary thyroid carcinomas. When there is a finding of thyroid incidentaloma, the radiologist should ask for serum thyrocalcitonin when the nodule displays Thyroid Imaging Reporting and Data System (TIRADS) 4A features, namely when located at the upper mid third junction of the thyroid lobe (C cell nest). The new TIRADS system classification of thyroid nodules is currently used by radiologists in Europe who have expertise in thyroid imaging and may help in classifying thyroid nodules from benign to malignant by use of five malignant criteria: nodule taller than wide, marked hypoechogenicity, presence of microcalcifications, stiffness, and irregular margins. Each specific TIRADS group corresponds with a probability of thyroid malignancy that leads to precise treatment selection from follow-up to fine-needle aspiration biopsy (FNAB) [4]. MRI may also provide important information enabling further characterization. Restriction of thyroid nodule diffusion is strongly correlated with hypercellularity and thyroid carcinoma. We think that whatever the size or age of the patient, thyroid nodules presenting with low apparent diffusion coefficient may also benefit from ultrasound characterization [5]. In conclusion, thyroid intranodular calcifications may be a sign of a clinically relevant thyroid malignancy and should be included in the three-tiered system, indicating further ultrasound exploration, FNAB (according to the TIRADS classification), and assess-

ing serum thyrocalcitonin level. Adding a diffusion-weighted MRI sequence may enable differentiation of benign from clinically relevant malignant thyroid nodules. Alexis Lacout Centre d’imagerie Médicale, Aurillac, France Mostafa El Hajjam Hôpital Ambroise PARE (APHP), Billancourt, France Pierre-Yves Marcy Polyclinique Les Fleurs, Ollioules, France DOI:10.2214/AJR.14.12595 WEB—This is a web exclusive article.

References 1. 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 2. Lang BH. The role of 18F-fluorodeoxyglucose positron emission tomography in the prognostication, diagnosis, and management of thyroid carcinoma. J Thyroid Res 2012; 2012:198313 3. Bai Y, Zhou G, Nakamura M, et al. Survival impact of psammoma body, stromal calcification, and bone formation in papillary thyroid carcinoma. Mod Pathol 2009; 22:887–894 4. Russ G, Bigorgne C, Royer B, Rouxel A, ­Bienvenu-Perrard M. The Thyroid Imaging Reporting and Data System (TIRADS) for ultrasound of the thyroid. J Radiol 2011; 92:701–713 5. Nakahira M, Saito N, Murata S, et al. Quantitative diffusion-weighted magnetic resonance imaging as a powerful adjunct to fine needle aspiration cytology for assessment of thyroid nodules. Am J Otolaryngol 2012; 33:408–416 (Figures start on next page)

AJR 2014; 203:W451 0361–803X/14/2034–W451 © American Roentgen Ray Society

AJR:203, October 2014 W451

Letters

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Fig. 1—68-year-old man with papillary thyroid carcinoma. A and B, CT (A) and ultrasound (B) images show calcified thyroid nodule (arrows) incidentally found on CT and proven to be papillary thyroid carcinoma. Thyroid nodule shows strong hypoechogenicity, psammoma microcalcifications, and ill-defined margins on ultrasound image. Thus, it should be classified into Thyroid Imaging Reporting and Data System category 5 (malignant).

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Fig. 2—77-year-old woman with thyroid medullary carcinoma who presented with left thyroid mass with calcifications. A and B, CT (A) and ultrasound (B) images show left thyroid mass with calcifications (thin arrows) and ipsilateral adenopathy (thick arrows). Small calcifications were better shown on ultrasound. High serum thyrocalcitonin level was consistent with medullar thyroid malignancy that was proven histologically.

AJR:203, October 2014

Three-tiered system for incidental thyroid nodules: do not forget the calcifications.

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