carcinoma of the thyroid gland is the most common endocrine malignancy , accounting in the usa for example for 95% of endocrine tumors . over the last 3 decades the incidence of well - differentiated thyroid cancer ( tc ) increased from 4.9 per 100 000 in 1975 to 14.3 per 100 000 in 2009 . in china , the standardized incidence of tc has increased from 1.6 per 100 000 in 1995 to 9.9 per 100 000 in 2010 . others are invasive early on , giving rise to clinical symptoms and metastasizing to lymph nodes . accurate and timely ultrasound ( us ) is the first - choice imaging modality for the diagnosis of tc . the diagnostic sensitivity , specificity , and accuracy rate are 92% , 72.9% , and 62~78% , respectively , for tc [ 57 ] . however , the sonograms of some lesions were overlapped between the benign and malignant as a result of the various ultrasonic appearances among different lesions . therefore , biopsy was relied on to get the final diagnosis , and is considered the diagnostic criterion standard [ 8 , 9 ] , but biopsy is invasive and has some risk for patients . previous studies showed that 4875% of patients who undergo biopsy are subsequently found to have benign lesions , the overall dissatisfaction rate for fna is between 1020% , and 2% of samples obtained by cnb are inadequate for histological diagnosis . how to reduce the number of unnecessary biopsies is an area of current research . contrast - enhanced ultrasound ( ceus ) scanning can detect differences in the distribution of blood and in the hemodynamics between tumors and surrounding tissues . it has found widespread application in many organs , such as the liver , gall bladder , and kidney . its use in assessing diseases of the thyroid gland has been the subject of a number of reports , although its precise role remains uncertain [ 1316 ] . ace / ame / eta ( american association of clinical endocrinologists / associazione medici endocrinology / european thyroid association ) guidelines in 2010 state that contrast agents provide only ancillary data for the diagnosis of malignant thyroid nodules and offer only a modest improvement over the information obtained with traditional color doppler or power doppler examinations , and that the use of us contrast agents should be restricted to defining the size of necrotic areas in lesions after us - guided ablation procedures . the 2013 nccn guidelines did not discuss the role of ceus scanning in diagnosing thyroid lesions . chinese tc diagnosis and therapy guidelines in 2012 state that the diagnostic value of ceus scanning should be explored in future studies . the enhancement patterns of thyroid nodules in previous studies were classified into low - enhancement , iso - enhancement , and high - enhancement , or homogeneous , heterogeneous , ring - enhancing , and no - enhancement , but no combination of them was reported in detail . in fact , variable thyroid nodules were observed during ceus scanning , and it may be that every each scan shows specific pathological changes . the peripheral ring of the lesion has been reported in previous papers , and ring enhancement was considered predictive of benign lesions . however , several kinds of peripheral rings were found in our clinical works , besides the common regular high - enhancement ring ( e.g. , irregular high - enhancement ring and no - enhancement ring ) . we decided to analyze the contrast enhancement patterns of the lesions and its peripheries on the basis of pervious research to assess the diagnostic value of ceus in thyroid nodules . the study was approved by the local ethics committee and those participating gave written informed consent . patients were eligible for inclusion if they were scheduled for thyroid biopsy as a consequence of having a palpable thyroid nodule or an abnormal ultrasound scan of the thyroid gland showing at least 1 of the following characteristics : hypoechogenicity , calcification , irregular or microlobulated margin , intranodular vascularity , and taller than wide . patients were excluded if they were known to be allergic to sulfur hexafluoride microbubbles ( sonovue ) or had a coagulation disorder . a total of 159 patients were identified , but 11 were excluded because no definite diagnosis was available . the mean sd age of the remaining 148 patients was 45.410.5 years ( range , 1671 years ) . between them a sequoia 512 ultrasound machine ( acuson , sequoia 512 encompass , siemens , usa ) and a 15l8w probe ( 814 mhz ) were used to image all patients . the contrast agent used was 59 mg dry powder sonovue ( bracco s.p.a inc . , this has a low mechanical index ( 0.200.23 ) and was administered intravenously at the elbow . the size , position , boundaries , internal structure , and blood supply of lesions were assessed . the ultrasound machine was then switched to ceus mode and the resulting images displayed on the monitor alongside the conventional gray - scale images . the real - time microbubble perfusion within lesions and surrounding tissues were observed for a minimum of 2 minutes and recorded on the ultrasound machine s internal hard drive . the recorded ceus images were reviewed and the degree of enhancement of the thyroid solid lesions was classified as : no - enhancement , low - enhancement , iso - enhancement , and high - enhancement . when enhancement was present , it was further assessed for the degree of homogeneity , producing the following lesion enhancement categories : ( 1 ) homogeneous low - enhancement , ( 2 ) heterogeneous low - enhancement , ( 3 ) homogeneous iso - enhancement , ( 4 ) heterogeneous iso - enhancement , ( 5 ) homogeneous high - enhancement , and ( 6 ) heterogeneous high - enhancement . the peripheral rings of nodules were divided into : ( 1 ) regular high - enhancement ring , ( 2 ) irregular high - enhancement ring , ( 3 ) regular no - enhancement ring , and ( 4 ) irregular no - enhancement ring . conversely , irregular rings were misshapen and their thickness was non - uniform . following ceus , a conventional biopsy of the thyroid lesion was performed on all patients , using an 18-gauge biopsy needle ( biopty ; bard , covington , ga , usa ) powered by an automatic biopsy device . the puncture position and direction were determined and monitored by ultrasound and non - enhancing areas on ceus were avoided . the biopsy specimens were examined by a single specialized thyroid pathologist with more than 15 years of experience . the ultrasonographer , the reviewer of the recorded ceus images , and the pathologist were all blinded to patient history and to each other s findings . all statistical analyses were performed using the statistical package for the social sciences ( spss ) software package , version 11.5 for windows ( spss inc . , the differences between lesion enhancement categories and the diagnostic value of conventional us and ceus were analyzed by pearson s chi - squared test (  ) . the relationship between the size of lesions and the lesion enhancement category was analyzed by f test . the study was approved by the local ethics committee and those participating gave written informed consent . patients were eligible for inclusion if they were scheduled for thyroid biopsy as a consequence of having a palpable thyroid nodule or an abnormal ultrasound scan of the thyroid gland showing at least 1 of the following characteristics : hypoechogenicity , calcification , irregular or microlobulated margin , intranodular vascularity , and taller than wide . patients were excluded if they were known to be allergic to sulfur hexafluoride microbubbles ( sonovue ) or had a coagulation disorder . a total of 159 patients were identified , but 11 were excluded because no definite diagnosis was available . the mean sd age of the remaining 148 patients was 45.410.5 years ( range , 1671 years ) . between them a sequoia 512 ultrasound machine ( acuson , sequoia 512 encompass , siemens , usa ) and a 15l8w probe ( 814 mhz ) were used to image all patients . the contrast agent used was 59 mg dry powder sonovue ( bracco s.p.a inc . , this has a low mechanical index ( 0.200.23 ) and was administered intravenously at the elbow . the size , position , boundaries , internal structure , and blood supply of lesions were assessed . the ultrasound machine was then switched to ceus mode and the resulting images displayed on the monitor alongside the conventional gray - scale images . the real - time microbubble perfusion within lesions and surrounding tissues were observed for a minimum of 2 minutes and recorded on the ultrasound machine s internal hard drive . the recorded ceus images were reviewed and the degree of enhancement of the thyroid solid lesions was classified as : no - enhancement , low - enhancement , iso - enhancement , and high - enhancement . when enhancement was present , it was further assessed for the degree of homogeneity , producing the following lesion enhancement categories : ( 1 ) homogeneous low - enhancement , ( 2 ) heterogeneous low - enhancement , ( 3 ) homogeneous iso - enhancement , ( 4 ) heterogeneous iso - enhancement , ( 5 ) homogeneous high - enhancement , and ( 6 ) heterogeneous high - enhancement . the peripheral rings of nodules were divided into : ( 1 ) regular high - enhancement ring , ( 2 ) irregular high - enhancement ring , ( 3 ) regular no - enhancement ring , and ( 4 ) irregular no - enhancement ring . following ceus , a conventional biopsy of the thyroid lesion was performed on all patients , using an 18-gauge biopsy needle ( biopty ; bard , covington , ga , usa ) powered by an automatic biopsy device . the puncture position and direction were determined and monitored by ultrasound and non - enhancing areas on ceus were avoided . the biopsy specimens were examined by a single specialized thyroid pathologist with more than 15 years of experience . the ultrasonographer , the reviewer of the recorded ceus images , and the pathologist were all blinded to patient history and to each other s findings . all statistical analyses were performed using the statistical package for the social sciences ( spss ) software package , version 11.5 for windows ( spss inc . , chicago , il , usa ) . the differences between lesion enhancement categories and the diagnostic value of conventional us and ceus were analyzed by pearson s chi - squared test (  ) . the relationship between the size of lesions and the lesion enhancement category was analyzed by f test . eighty - two lesions ( from 75 patients ) were malignant : papillary thyroid carcinoma ( 81 lesions ) , and medullary thyroid carcinoma ( 1 lesion ) . seventy - five lesions ( from 73 patients ) were benign : nodular goiter ( 43 lesions ) , follicular thyroid adenoma ( 15 lesions ) , hashimoto thyroiditis ( ht ) ( 10 lesions ) , chronic inflammation ( 3 lesions ) , subacute thyroiditis ( 2 lesions ) , oncocytic thyroid adenoma ( 1 lesion ) , and postoperative stitches ( 1 lesion ) . there were 137 solid lesions , and their contrast enhancement patterns are shown in table 1 . for each enhancement pattern , the difference between the benign and malignant lesions was significant ( =42.1334 ; p=0.000 ) . solid lesions that were malignant were found to have the following enhancement patterns on ceus scanning : 70.37% ( 57/81 ) low - enhancement ( including 75.44% heterogeneous patterns and 24.56% homogeneous patterns ) , 22.22% ( 18/81 ) iso - enhancement ( including 66.67% heterogeneous patterns and 33.33% homogeneous patterns ) , and 7.41% ( 6/81 ) heterogeneous high - enhancement . eighteen of 20 heterogeneous iso - enhancement lesions displayed iso - enhancement with focal low - enhancement regions ; the low - enhancement area comprised < 50% lesion , and 12 ( 66.67% , 12/18 ) lesions were malignant . twenty lesions were cystic - solid mixed ( figure 5 ) . among them , 15 lesions were showed iso - enhancement coexisting with no - enhancement ( 14 benign , 1 malignant ) , and 5 lesion was showed no - enhancement . in this group , all lesions with homogeneous high - enhancement and no - enhancement patterns were benign . with regards to lesions with low - enhancement appearance as malignant , the diagnostic sensitivity , specificity , and accuracy for tc were 84.15% , 65.33% , and 75.16% , respectively , for ceus scanning . no ring enhancement was seen in 117 lesions ( 74 malignant , 43 benign ) that had ill - defined margins . irregular ring high - enhancement was seen in 2 lesions ( figure 4c ) ; both were malignant . regular ring non - enhancement was seen in 6 lesions ( figure 3b ) ; 4 ( 67% ) were benign and the other 2 ( 33% ) were malignant . the differences of peripheral ring enhancement between malignant and benign lesions were significant ( =22.66 , p=0.000 ) . with regards to lesions with irregular rings as malignant , the diagnostic sensitivity , specificity , and accuracy for tc were 100% , 94.12% , and 95% , respectively , for ceus scanning . with regards to lesions with low - enhancement and/or a peripheral irregular ring as malignant criterion , the diagnostic sensitivity , specificity , and accuracy for tc were 88% , 65.33% , and 88.32% , respectively , for ceus scanning , whereas they were 98.88% , 42.67% and 71.97% , respectively , for tc by conventional us . the misdiagnosis rate was 57.33% for conventional ultrasound scanning and 34.67% for ceus scanning ( =7.76 , p=0.005 ) . there was a significant difference in the size of thyroid lesions between low - enhancement , iso - enhancement , high - enhancement , iso - enhancement with no - enhancement area , and no - enhancement ( f=11.44 , p=0.000 ) ( table 2 ) . no significant difference was found between lesions with high - enhancement and iso - enhancement with a non - enhancing area ( p>0.05 ) . eighty - two lesions ( from 75 patients ) were malignant : papillary thyroid carcinoma ( 81 lesions ) , and medullary thyroid carcinoma ( 1 lesion ) . seventy - five lesions ( from 73 patients ) were benign : nodular goiter ( 43 lesions ) , follicular thyroid adenoma ( 15 lesions ) , hashimoto thyroiditis ( ht ) ( 10 lesions ) , chronic inflammation ( 3 lesions ) , subacute thyroiditis ( 2 lesions ) , oncocytic thyroid adenoma ( 1 lesion ) , and postoperative stitches ( 1 lesion ) . there were 137 solid lesions , and their contrast enhancement patterns are shown in table 1 the difference between the benign and malignant lesions was significant ( =42.1334 ; p=0.000 ) . solid lesions that were malignant were found to have the following enhancement patterns on ceus scanning : 70.37% ( 57/81 ) low - enhancement ( including 75.44% heterogeneous patterns and 24.56% homogeneous patterns ) , 22.22% ( 18/81 ) iso - enhancement ( including 66.67% heterogeneous patterns and 33.33% homogeneous patterns ) , and 7.41% ( 6/81 ) heterogeneous high - enhancement . eighteen of 20 heterogeneous iso - enhancement lesions displayed iso - enhancement with focal low - enhancement regions ; the low - enhancement area comprised < 50% lesion , and 12 ( 66.67% , 12/18 ) lesions were malignant . twenty lesions were cystic - solid mixed ( figure 5 ) . among them , 15 lesions were showed iso - enhancement coexisting with no - enhancement ( 14 benign , 1 malignant ) , and 5 lesion was showed no - enhancement . in this group , all lesions with homogeneous high - enhancement and no - enhancement patterns were benign . with regards to lesions with low - enhancement appearance as malignant , the diagnostic sensitivity , specificity , and accuracy for tc were 84.15% , 65.33% , and 75.16% , respectively , for ceus scanning . no ring enhancement was seen in 117 lesions ( 74 malignant , 43 benign ) that had ill - defined margins . irregular ring high - enhancement was seen in 2 lesions ( figure 4c ) ; both were malignant . regular ring non - enhancement was seen in 6 lesions ( figure 3b ) ; 4 ( 67% ) were benign and the other 2 ( 33% ) were malignant . the differences of peripheral ring enhancement between malignant and benign lesions were significant ( =22.66 , p=0.000 ) . with regards to lesions with irregular rings as malignant , the diagnostic sensitivity , specificity , and accuracy for tc were 100% , 94.12% , and 95% , respectively , for ceus scanning . with regards to lesions with low - enhancement and/or a peripheral irregular ring as malignant criterion , the diagnostic sensitivity , specificity , and accuracy for tc were 88% , 65.33% , and 88.32% , respectively , for ceus scanning , whereas they were 98.88% , 42.67% and 71.97% , respectively , for tc by conventional us . the misdiagnosis rate was 57.33% for conventional ultrasound scanning and 34.67% for ceus scanning ( =7.76 , p=0.005 ) . there was a significant difference in the size of thyroid lesions between low - enhancement , iso - enhancement , high - enhancement , iso - enhancement with no - enhancement area , and no - enhancement ( f=11.44 , p=0.000 ) ( table 2 ) . no significant difference was found between lesions with high - enhancement and iso - enhancement with a non - enhancing area ( p>0.05 ) . ceus enhancement patterns were found to be different in benign and malignant thyroid lesions , but its contribution to the diagnosis of thyroid cancer is controversial . in our study , we found a variety of patterns of contrast enhancement in benign and malignant thyroid lesions . two of these patterns , iso - enhancement with a focal low - enhancement region within the lesion and a non - enhancing ring in the periphery of the lesion , have not been reported previously . we found the pattern of iso - enhancement with a focal low - enhancing area to be common with malignant lesions . on biopsy , both the focal low - enhancing area and the surrounding part of the lesion showing iso - enhancement contained malignant cells , and the focal low - enhancing area also showed evidence of interstitial fibrosis . hypo - vascularity is often observed in focal ht , which is associated with focal hypothyroidism with severe follicular degeneration . twenty lesions were benign , including 2 that were ht , 2 that were chronic inflammation , 1 case of subacute thyroiditis , and 1 postoperative suture . these lesions demonstrated heterogeneous low - enhancement within the lesion , without a peripheral ring . . the enhancement pattern in the periphery of lesions may provide useful diagnostic information , especially for those lesions with internal iso - enhancement appearances . regular high - enhancing rings were only found in benign lesions , especially in adenoma and nodular goiter . the vascularity of the surface capsule or the compressed tissue around lesion is the explanation for the high - enhancement ring at the periphery of the lesion . the ability of ceus to detect these features is useful in differentiating cancer from benign lesions . regular no - enhancement could be found both in benign and malignant nodules . in this group , 6 nodules had peripheral regular no - enhancement rings , in which 4 were benign ( 2 were adenoma ) and 2 malignant ( all were ptc ) . the presence of a non - enhancing ring in the periphery of lesions may reflect changes in tissues adjacent to the lesion , which might be a consequence of inflammatory exudate , interstitial edema , or mucoid degeneration because of strong pressure from the nodule . the pathological cause for an irregular non - enhancing peripheral ring is unclear , but it is possible that it reflects irregular invasion of cancerous tissue into adjacent tissues . peripheral irregular high - enhancement rings may result from interstitial angiogenesis hyperplasia caused by the cancerous cells invasion . generally , the visible range of lesions was larger on ceus than on gray - scale us in lesions with irregular high - enhancement ring . one of 15 cystic - solid mixed lesions in this group was ptc , and it showed iso - enhancement with non - enhancing areas . on conventional us , some tiny  spots of blood signals were shown in the solid component of the lesion . with ceus scanning , the solid component showed heterogeneous iso - enhancement without a peripheral ring . the other 14 benign lesions showed homogeneous iso - enhancement in solid component with regular high - enhancing rings or non - enhancing rings . all lesions that failed to show any enhancement were benign . on conventional us scanning , they had a cystic - solid appearance . pathological results showed that many of these lesions were nodular goiters with areas of hemorrhage and the ceus appearances , suggesting that the apparently solid areas were not perfused by contrast agent . was related to the size of lesions , which is in agreement with a previous report . in our study , most malignant lesions showing low - enhancement were papillary thyroid microcarcinomas , perhaps due to the small or immature vascular network in microcarcinomas . the compression of blood vessels by cancer cells can increase resistance to blood flow and impair blood supply . conventional us detected tc with a high sensitivity , so the misdiagnosis rate is our concern . this study showed that ceus can clearly reduce the misdiagnosis rate compared with conventional us ( p<0.01 ) . our study shows that : ( 1 ) with ceus , the appearances of ht and other inflammatory disorders of the thyroid gland overlap with those of malignant thyroid disease . ( 2 ) ceus appearances of homogeneous hyper- , iso- , and no- enhancement within lesions and/or regular high - enhancement ring in the peripheries of lesions are suggestive of benign thyroid lesions . if there is doubt , conventional us scanning these appearances on ceus scanning may be helpful pre - operatively . ( 3 ) lesions showing iso - enhancement with a focal low - enhancement region should be considered malignant if inflammatory disease has been excluded . in patients with suspicious us characteristics , ceus had high specificity and contributed to establishing the diagnosis .