To investigate the diagnostic value of computed tomography（CT）histogram analysis for thyroid malignant solitary coarse calcification nodules（MSCN）.
A total of 89 thyroid solitary coarse calcification nodules（coarse calcification ≥5 mm, no definite soft tissue around calcification）confirmed either by surgery or histopathological examination in 86 patients enrolled in this study from Jan. 2009 to Dec. 2015 were evaluated, including 33 MSCN from 32 patients and 56 benign solitary coarse calcification nodules （BSCN）from 56 patients. Overall, 27 cut-off values were calculated by N（4≤N≤30）times of 50 Hounsfield units （HU）in the range of 200 HU to 1500 HU, and each cut-off value and the differences in the corresponding area percentages in the CT histogram were recorded for MSCN and BSCN. The optimal cut-off value and the corresponding area percentage were established by receiver operating characteristic（ROC）curve analysis.
In the 24 groups with an ROC area under the curve（AUC）of more than 0.7, at a cut-off value of 1150 HU and at an area percentage of no less than 98.4%, the ROC AUC reached a maximum of 0.86, and the accuracy, sensitivity, and specificity were 70.8%, 93.9%, and 57.1%, respectively. At a cut-off value of 450 HU and at an area percentage of no less than 46.3%, the accuracy, sensitivity, and specificity were 76.4%, 48.5%, and 92.9%, respectively. At a cut-off value of 550 HU and at an area percentage of no less than 81.5%, the accuracy, sensitivity, and specificity were 75.3%, 33.3%, and 100%, respectively.
In comparison with the cut-off value of 1150 HU with an area percentage of no less than 98.4%, the sensitivities for the cut-off value of 450 HU with an area percentage of no less than 46.3% and for the cut-off value of 550 HU with an area percentage of no less than 81.5% were lower; however, the specificities increased significantly, providing an important basis for reducing the misdiagnosis of MSCN.
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Calcification is a common radiographic sign of thyroid nodules, and it is often accidentally discovered during ultrasonography or computed tomography（CT）of the neck as well as in chest CT or plain radiographic examination. The discovery of microcalcifications in thyroid nodules by ultrasonography is suggestive of malignancy[1,2,3,4,5]. However, because of obvious echo attenuation caused by coarse calcifications and different classification methods used by different researchers for coarse calcification subtypes, there exist great differences in the conclusions regarding their diagnostic value[6,7]. Although fine-needle aspiration biopsy （FNAB）has been regarded as the optimal method for differentiating benign from malignant thyroid nodules[1, 8,9], it is hard for the fine needle to penetrate the hard, thick calcified nodules; further, even if penetration is achieved, it is difficult to obtain adequate histological specimens, rendering the diagnosis difficult[6,7]. CT examination is not restricted by echo attenuation and can fully show the size, shape, and density of the calcification, and this density is an important parameter. Holtz et al[10] considered that certain differences existed in the density of calcifications between benign nodules and malignant nodules in the thyroid, with greater density observed in benign nodules than in malignant ones. For solitary coarse calcifications of uneven density, it is hard to accurately gauge the density using the density of one or more points. Our previous studies have shown that calcification artifacts were more common in high-density benign solitary coarse calcifications; however, the specificity of the diagnosis of benign solitary coarse calcification nodules （BSCN）was only 76.9%[11], and this judgment was likely to be influenced by certain subjective factors. The CT histogram can reflect the pixel densities of various areas of interest, this study aimed to analyze CT histograms in malignant solitary coarse calcification nodules（MSCN）and BSCN and explore the diagnostic value of CT histograms in differentiating between MSCN and BSCN.
