patients who were diagnosed with papillary carcinoma or microcarcinoma and underwent surgery at severance hospital from january to june 2011 were included in this study . ten cases of total thyroidectomy specimens with papillary carcinoma or microcarcinoma were randomly selected in age- ( 3rd to 7th decades ) and sex - matched pairs . a representative hematoxylin and eosin ( h&e ) all of these patients had neither a medical history of hypertension or diabetes , nor a history of surgery for vascular diseases . the study design and case selection were identical to the retrospective study , but in the prospective study , the entire unilateral thyroid gland containing the papillary carcinoma or microcarcinoma was serially dissected , sampled , and evaluated for each patient . we defined the location of vessels as either extrathyroid or intrathyroid by drawing imaginary lines in uncertain areas . the thyroid tissue sections that were 3 m in thickness , fixed in 10% formalin , and embedded in paraffin blocks , were used for histological analysis with routine h&e staining , along with special and immunohistochemical stains of elastic van gieson ( evg ) and s-100 protein . using h&e stain to identify the types of vessels as either arteries or veins , the number of arteries was counted , and the arterial wall thickness between the intimal lining and external elastic lamina was precisely measured and eventually corrected for errors of sectioning and analysis . we performed a special staining of evg,15 and an additional immunohistochemical staining of s-100 protein was completed to confirm the absence of nerve tissue in the thyroid parenchyma , as performed in previous studies.2 for comparing the extrathyroid and intrathyroid arterial and arteriolar wall thicknesses , we initially counted and measured the entire detectable artery . however , several large arteries in the thyroid gland could be a part of the branching arteries penetrating the thyroid along the interlobular spaces.2 in addition , diagnostic problems , that is whether the cancer extended to the extrathyroid tissue or was confined to the intrathyroid region , occurred when the cancer locations were not definitive . as a result , definite arteries and arterioles located in the intrathyroid and interlobular areas were excluded . therefore , we decided not to include arteries or arterioles in the thyroid parenchyma that were greater than 2 mm from the surface . we measured the arterial and arteriolar wall thicknesses , the distance between the intimal endothelium and external elastic lamina , which refers to the sum of the tunica intima and tunica media15 using the image j program , a computer - based morphometric analysis programs ( fig . 1).16 to avoid bias , we randomly measured the thicknesses six times , for example , at 12 , 2 , 4 , 6 , 8 , and 10 o'clock , in each blood vessel17,18 and we then used the mean thicknesses as statistical data , as shown in fig . a two - tailed independent student 's t - test and pearson 's simple correlation coefficient were used for the continuous variables of the two independent groups in both of the studies . patients who were diagnosed with papillary carcinoma or microcarcinoma and underwent surgery at severance hospital from january to june 2011 were included in this study . ten cases of total thyroidectomy specimens with papillary carcinoma or microcarcinoma were randomly selected in age- ( 3rd to 7th decades ) and sex - matched pairs . a representative hematoxylin and eosin ( h&e ) all of these patients had neither a medical history of hypertension or diabetes , nor a history of surgery for vascular diseases . the study design and case selection were identical to the retrospective study , but in the prospective study , the entire unilateral thyroid gland containing the papillary carcinoma or microcarcinoma was serially dissected , sampled , and evaluated for each patient . we defined the location of vessels as either extrathyroid or intrathyroid by drawing imaginary lines in uncertain areas . the thyroid tissue sections that were 3 m in thickness , fixed in 10% formalin , and embedded in paraffin blocks , were used for histological analysis with routine h&e staining , along with special and immunohistochemical stains of elastic van gieson ( evg ) and s-100 protein . using h&e stain , we were able to screen sections of thyroid tissue . to identify the types of vessels as either arteries or veins , the number of arteries was counted , and the arterial wall thickness between the intimal lining and external elastic lamina was precisely measured and eventually corrected for errors of sectioning and analysis . we performed a special staining of evg,15 and an additional immunohistochemical staining of s-100 protein was completed to confirm the absence of nerve tissue in the thyroid parenchyma , as performed in previous studies.2 for comparing the extrathyroid and intrathyroid arterial and arteriolar wall thicknesses , we initially counted and measured the entire detectable artery . however , several large arteries in the thyroid gland could be a part of the branching arteries penetrating the thyroid along the interlobular spaces.2 in addition , diagnostic problems , that is whether the cancer extended to the extrathyroid tissue or was confined to the intrathyroid region , occurred when the cancer locations were not definitive . as a result , therefore , we decided not to include arteries or arterioles in the thyroid parenchyma that were greater than 2 mm from the surface . we measured the arterial and arteriolar wall thicknesses , the distance between the intimal endothelium and external elastic lamina , which refers to the sum of the tunica intima and tunica media15 using the image j program , a computer - based morphometric analysis programs ( fig . 1).16 to avoid bias , we randomly measured the thicknesses six times , for example , at 12 , 2 , 4 , 6 , 8 , and 10 o'clock , in each blood vessel17,18 and we then used the mean thicknesses as statistical data , as shown in fig . a two - tailed independent student 's t - test and pearson 's simple correlation coefficient were used for the continuous variables of the two independent groups in both of the studies . a total of 297 and 19,843 arteries were counted in ten retrospective and ten prospective analyses , respectively . in the retrospective study , the extrathyroid arteries and arterioles ( n=164 ) outnumbered the intrathyroid ones ( n=133 ) . in the prospective study , the extrathyroid arteries and arterioles ( n=6,020 ) were fewer in number than the intrathyroid ones ( n=13,823 ) . the mean wall thicknesses of the extrathyroid arteries ( 26.88 m and 35.24 m , respectively , from the retrospective and prospective studies ) were thicker ( p=0.000 ) than the intrathyroid arteries and arterioles ( 15.07 m and 16.52 m , respectively , from the retrospective and prospective studies ) . the respective ranges of the mean thicknesses of the blood vessels in the extrathyroid and intrathyroid tissues were 3.84 to 226.43 m and 3.25 to 67.93 m , respectively from the 20 total patients ( table 1 ) . the wall thickness comparison between the sexes according to the location of the arteries is shown in table 2 . counting the number of the observed total arteries and arterioles demonstrated that male patients ( n=11,535 ) had more arteries than female patients ( n=8,605 ) . this discrepancy was also seen in the number of extrathyroid ( m , 3,217 ; f , 2,967 ) and intrathyroid ( m , 8,318 ; f , 5,638 ) arteries for all of the cases . in male patients , the mean extrathyroid arterial walls ( 23.47 m and 32.11 m ) were thicker than the intrathyroid arterial walls ( 14.33 m and 14.22 m ) in the preliminary ( p=0.001 ) and prospective studies ( p= 0.000 ) , respectively . likewise , the female patients revealed similar results , with the mean extrathyroid arterial walls ( 29.83 m and 38.66 m ) being thicker than the intrathyroid arterial walls ( 15.78 m and 19.93 m ) in the preliminary ( p=0.000 ) and prospective studies ( p=0.000 ) , respectively . table 3 shows that there was no significant difference in the mean extrathyroid ( p=0.083 ) or intrathyroid ( p=1.000 ) arterial wall thicknesses between the male and female patients in the preliminary study . however , in the prospective study , a comparison between the paired mean extrathyroid ( p=0.000 ) and intrathyroid ( p=0.000 ) arterial wall thicknesses demonstrated that the male arteries ( 32.11 m and 14.22 m ) were thinner than female arteries ( 38.66 m and 19.93 m ) , respectively . we identified the correlations between the arterial wall thicknesses and age groups in the prospective cases ( table 4 ) . all five age groups ( 3rd to 7th decades ) revealed that the mean arterial wall thicknesses in the extrathyroid tissue was thicker than the mean arterial wall thicknesses in the intrathyroid tissue ( p=0.000 ) . in each age group , the mean wall thicknesses of the arteries in the extrathyroid and intrathyroid tissues exhibited significant differences ( p=0.000 ) in ascending order ( from 3rd to 7th decades ) as follows : 36.15 vs. 18.71 , 34.30 vs. 17.99 , 32.68 vs. 17.20 , 34.59 vs. 14.89 , and 37.44 vs. 15.25 . when comparing among the age groups , a decreasing tendency in the intrathyroid arterial wall thickness with increasing age was seen ( p=0.01 ) . on the other hand , the extrathyroid arterial wall thicknesses did not exhibit any significant relationship to age ( p=0.09 ) . in addition , nerve tissues were not identified in the thyroid parenchyma itself , but in all of the cases , some nerve tissues in the interlobular septum were identified by using immunohistochemical staining for s-100 protein ( fig . through the practice of surgical pathology , we found many difficulties in determining the extent of the tumors for diagnosing papillary carcinomas or papillary microcarcinomas of the thyroid gland . according to the primary tumor stage ( t ) , the t3 stage classification was determined when the tumor size was greater than 4 cm in size in its greatest dimension , was limited to the thyroid parenchyma , or had any cancer with minimal ete . even though the anatomic stage / prognostic groups for papillary carcinomas in the patients younger than 45 years included had only two stages ( i , ii ) whether metastasis was present or not , the t stage could be an important parameter for determining the prognostic groups of patients 45 years and older.7 - 10 because of this significance , pathologists should discretely judge whether tumors are limited to the thyroid . searching previous articles and textbooks , however , we could not find discrete clarifying parameters of minimal ete . therefore , we focused on the aspect of " sizable blood vessels " in determining minimal ete.5 in this study , we found that the mean thickness of the extrathyroid arteries were greater than that of the intrathyroid arteries in both retrospective and prospective studies . in all of the cases , the extrathyroid arteries were 1.78 and 2.13 times thicker than the intrathyroid arteries in the retrospective and prospective studies , respectively . the thinnest extrathyroid artery was 3.84 m in thickness , while the thickest intrathyroid artery was 67.93 m in thickness . in the male group , the extrathyroid arteries were 1.64 and 2.26 times thicker than the intrathyroid arteries in the retrospective and prospective studies , respectively . in the female group , the extrathyroid arteries were 1.89 and 1.94 times thicker than the intrathyroid arteries in the retrospective and prospective studies , respectively . in other words , the arteries in the extrathyroid tissue were about two times thicker than arteries in thyroid parenchyma . the retrospective study revealed that extrathyroid arteries ( n=164 ) were greater in number than the intrathyroid arteries ( n=133 ) , but the prospective study revealed the opposite results ( 6,020 vs. 13,823 ) for extrathyroid and intrathyroid arteries , respectively . one potential reason for this was that each representative slide in the ten prospective cases included papillary carcinomas or papillary microcarcinomas . as a result , the area of thyroid parenchyma that could be examined decreased . comparing the number of arteries between the sexes we also found that the extrathyroid and intrathyroid arteries exhibited no differences based on sex in the retrospective study . however , the prospective study revealed that the arteries in the female were 1.20 and 1.40 times thicker than those in males in the extrathyroid and intrathyroid tissues , respectively . a correlation was not identified in the age differences in the retrospective study due to the limited number of cases . in the prospective study , the total number of arteries revealed that the 6th decade group had the most arteries ( n=4,903 ) , while the 3rd decade group exhibited the fewest number of arteries ( n= 2,797 ) . the relationships among age groups in the 3rd , 4th , 5th , 6th , and 7th decades were analyzed in the prospective study as follows : 1 ) all five age groups revealed that the arteries in the extrathyroid tissue were thicker than in the intrathyroid tissue , 2 ) in each decade , the results of the differences of the arterial wall thicknesses between the location of the arteries increased in ascending order of age with the extrathyroid arteries being 1.93 , 1.90 , 1.90 , 2.32 , and 2.43 times thicker than the intrathyroid arteries , respectively . for all of the cases , a two - fold difference in thickness of the extrathyroid and intrathyroid arterial walls was seen . in addition , we confirmed that nerve tissue did not exist in the thyroid parenchyma , in agreement with previous studies.3 previous studies have only mentioned the " sizable blood vessels " as one of the factors determining the boundary between intrathyroid and extrathyroid tissues , whereas our study presented the " sizable blood vessels " numerically . however , the number of patients was insufficient to establish numeric criteria for sizable blood vessels . we also calculated the mean thicknesses of the arteries and arterioles by randomly measuring each artery and arteriole a total of six times , as performed in previous studies.17,18 further larger studies are required in order to establish new criteria for sizable blood vessels and should include more precise measurement methods . with the publication of investigations about the prognostic differences according to minimal ete , the demand for realistic criteria of sizable blood vessels will increase . in conclusion , the retrospective study exhibited differences between extrathyroid and intrathyroid arterial and arteriolar wall thicknesses regardless of sex . the prospective study revealed that extrathyroid arteries were thicker than intrathyroid arteries in all 20 cases regardless of sex or age group . of the total 20 patients , the ranges of the mean thicknesses of the blood vessels in the extrathyroid and intrathyroid tissues were 3.84 to 226.43 m and 3.25 to 67.93 m , respectively . therefore , we suggest that the sizable blood vessel of extrathyroid arteries can be expected to be greater than 67.93 m in thickness .
backgroundto define the exact boundary of the intrathyroid and extrathyroid aspects of a gland when determining the extent of cancer invasion , we plan to clarify the definition of sizable vascular structures , which is one of the helpful histologic clues in determining a minimal extrathyroid extension . 
 we hypothesized that arterial wall thicknesses in extrathyroid soft tissue would be significantly different from the arteries in the thyroid parenchyma.methodstwenty cases of papillary carcinoma were selected . 
 the numbers and wall thicknesses of the arteries and arterioles in intrathyroid and extrathyroid tissue were evaluated . 
 the absence of nerve tissue in the thyroid gland was confirmed using the s-100 protein immunohistochemical stain.resultsthe comparison of the mean thicknesses of the total arteries between the extrathyroid and intrathyroid tissues in the retrospective study ( 26.88 m vs. 15.07 m , respectively ) and the prospective study ( 35.24 m vs. 16.52 m , respectively ) revealed significant differences ( p=0.000 ) . 
 the greatest thickness of the intrathyroid arteries was 67.93 m.conclusionsaccording to our results , the study showed that the extrathyroidal arteries were significantly thicker than the intrathyroidal arteries . 
 we suggest that the sizable blood vessels of extrathyroidal arteries should be greater than 67.93 m in thickness .