Original Article pissn 1738-2637 / eissn 2288-2928 J Korean Soc Radiol 2013;69(4):269-273 http://dx.doi.org/10.3348/jksr.2013.69.4.269 CT Detection of Thyroid Pyramidal Lobe in Preoperative Patients with Thyroid Tumors Gi Won Shin, MD, Dong Wook Kim, MD Department of Radiology, Busan Paik Hospital, Inje University College of Medicine, Busan, Korea Purpose: Thyroid pyramidal lobe (TPL) is a normal variant of the thyroid gland, but few imaging studies of TPL have been published. The purpose of this study is to investigate the frequency, location, size (length, maximal AP diameter, maximal transverse diameter), and upper end level of TPL with its separation from the main thyroid gland on preoperative neck CT and to compare them with operative findings in order to assess the diagnostic accuracy of neck CT for detection TPL. Materials and Methods: 46 patients, who underwent preoperative neck CT before thyroidectomy, were included in the study. The frequency, location, size, and upper end level of TPL with its separation from the main thyroid gland on the neck CT was analyzed by a single radiologist. Results: The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of neck CT for detecting TPL was 77.8%, 89.5%, 91.3%, 73.9% and 82.6%. There was a significant difference in maximal AP diameter, location, upper end level, and its separation from main thyroid gland between CT and operative findings (p < 0.05), but there was no significant difference in the length and maximal transverse diameter of TPL (p > 0.05). Conclusion: Diagnostic accuracy of neck CT for detecting TPL was high, and the neck CT may be useful for evaluating TPL in the suprahyoid neck. Index terms Thyroid Gland Pyramidal Lobe Preoperative Period Neck CT Diagnostic Index Received June 19, 2013; Accepted July 16, 2013 Corresponding author: Dong Wook Kim, MD Department of Radiology, Busan Paik Hospital, Inje University College of Medicine, 75 Bokji-ro, Busanjin-gu, Busan 614-735, Korea. Tel. 82-51-890-6549 Fax. 82-51-896-1085 E-mail: dwultra@lycos.co.kr This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 서론 갑상선암은최근한국에서유병률이급격히증가하고있으며, 여성에서가장흔한암종으로, 갑상선암의발견및치료의빈도가급속히증가되었다 (1). 갑상선유두암은적절한치료후에매우높은완치율을보이고예후가좋음에도불구하고적지않은빈도에서재발을보인다 (2, 3). 갑상선유두암의 TNM 병기결정에따라서수술범위를결정하게되지만, 갑상선전절제술후방사성동위원소치료를하는경우는흔하다 (4). 방사성동위원소치료는정상적인갑상선세포가남아있는경우, 방사성동위원소가갑상선암세포보다정상갑상선세포에대한친화력이높아치료효과가떨어질수있다 (5). 특히, 갑상선으로부터멀리떨어진피라미드엽은전체갑상선조직을제거하는갑상선전절제술시에도남겨질수있는데, 이는갑상선전절제술후이어지는방사성동위원소치료에영향을줄수있다 (5). 갑상선피라미드엽은기존의갑상선해부학적연구에서 15~ 75% 까지다양하게보고된다 (6, 7). 최근전산화단층촬영을이용한피라미드엽의빈도, 위치, 크기등에관한연구에서전산화단층촬영이피라미드엽의진단에유용하다고보고하였다 (8, 9). 하지만, 지금까지전산화단층촬영에서피라미드엽의빈도를조사한소수의연구만있을뿐전산화단층촬영과수술장에서의피라미드엽을조사및비교한연구는없다. 따라서, 본연구의목적은경부전산화단층촬영에서피라미드엽의빈도, 위치, 크기 ( 길이, 최대전후직경, 최대횡경 ), 상연및주갑상선과의분리여부를조사하여그결과를수술소견과비교하여피라미드엽에대한경부전산화단층촬영의진단정확성을알아보는것이다. 대상과방법 2013 년 1 월부터 2 월까지, 본원에서갑상선절제술을시행받 Copyrights 2013 The Korean Society of Radiology 269
았던환자중에서갑상선수술에대한기왕력이없으며, 내시경수술이아닌고식적인갑상선수술을받고, 수술전경부전산화단층촬영을받았던환자를대상으로하였다. 갑상선암 (n = 45) 의치료와양성갑상선결절의제거 (n = 1) 를이유로갑상선수술이시행되었다. 전산화단층촬영기기는 Aquillion One (Toshiba, Tokyo, Japan) 을사용하였고, 3 mm 두께슬라이스로비조영증강축면영상, 조영증강축면영상및조영증강관상면재구성영상을얻었다. 10 년이상의두경부영상판독경력을가진한명의영상의학과전문의가수술결과에대한정보없이 picture archiving and communication system 을이용하여경부전산화단층촬영에서갑상선피라미드엽의존재여부와위치, 크기, 상연, 주갑상선과의분리여부에대하여평가하였다. 경부전산화단층촬영에서갑상선피라미드엽은주갑상선으로부터위쪽으로돌출하는갑상선조직이적어도세개이상의축상면영상에서보일때로정의하였다. 위치는피라미드엽의기 시부위에따라서다음의그룹으로분류되었다 : 1) 우측성, 2) 중심선, 3) 좌측성, 4) 양측성. 피라미드엽의크기는길이, 전후직경, 횡경으로나누어서조사하였으며각각의최대직경을측정하였다 (Fig. 1). 피라미드엽의상연은위치에따라 1) 혀기저부, 2) 설골, 3) 갑상설골막, 4) 갑상연골의 4개의그룹으로분류하였다. 축상면전산화단층영상에서피라미드엽이주갑상선으로부터시작되어한슬라이스이상보이지않을때를피라미드엽이분리되어있다고정의하였다. 한명의외과의가갑상선수술을하였으며, 갑상선과피라미드엽을절개한직후계측기를이용하여피라미드엽의크기를측정하였다. 갑상선수술을통하여조사된피라미드엽에대한결과를기준으로하여, 경부전산화단층촬영을이용한피라미드엽의진단에대한민감도, 특이도, 양성예측도, 음성예측도및정확도를계산하였다. 또한 Fisher s exact test 를이용하여빈도, 위치, 크기, 상연및주갑상선과의분리여부에따른진단정확도를비교분석하였다. p값이 0.05 보다낮을때통계적으로유의한것으로간주하였고데이터분석은 SPSS 를통해이뤄졌다 (version 17.0.1; SPSS Inc., Chicago, IL, USA). 결과 Fig. 1. Size measurement of thyroid pyramidal lobe in CT image on a picture archiving and communication system. Maximal anteroposterior (A) and transverse (B) diameters of thyroid pyramidal lobe are measured in axial images. The length of thyroid pyramidal lobe are determined according to the number of axial images showing thyroid pyramidal lobe. 총 46명 ( 여성 43명, 남성 3명 ; 연령범위 31~70 세 ; 평균연령 48.0세 ) 이아래목깃절개술 (low-collar incision) 을통한갑상선수술을받았으며, 45명에서갑상선유두암이확진되었고 1 명에서결절성비후가확진되었다. 경부전산화단층촬영과수술에서는각각 23명 (50%) 과 27명 (58.7%) 에서피라미드엽이확인되었다 (Fig. 2). 경부전산화단층촬영의피라미드엽의발견 (detection) 에대한진단에서진양성, 진음성, 위양성및위음성률은각각 77.8%, 89.5%, 8.6% 및 26.0% 였으며, 82.6% 의진단정확도를보였다 (Table 1). A B C Fig. 2. A 52-year-old man with a right pyramidal lobe detected on neck CT and in surgery. Nonenhanced axial (A) and contrast-enhanced axial (B) CT images show the right pyramidal lobe (arrow) with the same attenuation and enhancement as the main thyroid gland (arrowheads). The right pyramidal lobe (C) is observed during thyroid surgery (arrow). 270 대한영상의학회지 2013;69(4):269-273 jksronline.org
신기원외 경부전산화단층촬영과수술에서조사된피라미드엽의빈도, 위치, 크기, 상연, 그리고주갑상선과의분리여부의결과는 Table 2에요약하였다. 피라미드엽의전후직경에있어서는경부전산화단층촬영과수술결과가서로유의한차이를보였으나 (p = 0.009, Fisher s exact test), 피라미드엽의길이와횡경에있어서는차이를보이지않았다 (p > 0.05, Fisher s exact test). 또한, 피라미드엽의위치, 상연, 주갑상선과의분리여부에있어서는경부전산화단층촬영과수술결과가통계학적으로유의한차이를보였다 (p < 0.05, Fisher s exact test). 경부전산화단층촬영과수술결과모두에서 1예의부갑상선 (accessory thyroid) 이관찰되었다. 고찰 갑상선암의술전평가에서전산화단층촬영의역할은갑상선암의주위중요장기에대한침범유무를판별하고목이나종격동의림프절전이가있는지평가하는것이다 (10). 특히, 갑상선유두암환자에서술전초음파검사나전산화단층촬영등의영상연구나조직검사에서림프절전이가의심되면광범위경부림프절절제술을병행한갑상선전절제술을시행받는다. 또한, 수술로제거되는갑상선주위림프절의갑상선암의전이나고위험환자여부에따라술후방사성동위원소치료를시행한다 (11). 방사성동위원소치료에서투여된방사성동위원소는악성갑상선 세포보다는정상갑상선세포에더높은친화력을보이며, 따라 서술후남아있는정상갑상선세포가없을때효과적이므로 (12), 술후시행하게될지모르는방사성동위원소치료를위해 서갑상선전절제술시정상갑상선세포가남아있지않도록해야 한다. 특히, 피라미드엽이나다른갑상선변이에대한적절한술 전평가가되지않으면수술후불필요한정상갑상선세포가남 아있을수있다. 갑상선은전방경부하부에위치한내분비기관으로경부 5 번에서흉부 2 번척추레벨에있으며, 갑상선의변이에는이소 성갑상선, 피라미드엽, 부갑상선등이포함된다. 피라미드엽은 발생과정에서인두의기저부에서갑상선게실이형성되어하강 하는과정에서생긴갑상설관낭의하부를반영하며 (13), 발생 빈도는보고자에따라 15% 에서 75% 까지다양하다 (6, 7). 최 근경부전산화단층촬영에서의갑상선피라미드엽을조사한연 Table 1. The Diagnostic Index of Neck CT for the Detection of Thyroid Pyramidal Lobe Sensitivity 77.8% (21/27) Specificity 89.5% (17/19) Positive predictive value 91.3% (21/23) Negative predictive value 73.9% (17/23) Accuracy 82.6% (38/46) Table 2. Comparison in Size and Upper End of Pyramidal Lobe between CT and Surgical Findings in 46 Patients CT Surgery p Value* Frequency (N) 50% (23/46) 58.7% (27/46) Size (mean ± SD) Length (mm) 26.0 ± 8.9 27.7 ± 10.4 0.444 Anteroposterior diameter (mm) 3.1 ± 1.7 2.4 ± 0.8 0.009 Transverse diameter (mm) 7.7 ± 2.7 7.1 ± 2.9 0.833 The level of upper end (N) 0.002 Tongue base 0 0 Hyoid bone 8 6 Thyrohyoid membrane 3 8 Thyroid cartilage 12 13 Location (N) < 0.001 Right pyramidal lobe 6 9 Midline pyramidal lobe 5 4 Left pyramidal lobe 12 14 Bilateral 0 0 Separation (N) 0.001 Separation 1 2 No separation 22 25 Note. Data presented in parentheses are the percentage of each item. *p value in each items difference between male and female. N = number jksronline.org 대한영상의학회지 2013;69(4):269-273 271
구에따르면피라미드엽은미만성갑상선질환의동반여부와관계없이주갑상선과같은감쇠 (attenuation) 와조영증강을보인다고하였다 (8, 9). 본연구에서조사된피라미드엽의빈도는경부전산화단층촬영과수술에서각각 50% 와 58.7% 로관찰되었는데, 경부전산화단층촬영을이용한다기관연구에서발견된 44.6%(981/2200) 보다높았다 (9). 168 구의한국성인시신을대상으로조사한연구에서는 76.8% 에서피라미드엽이관찰되어, 본연구의수술소견에서보인 58.7% 보다높았으며 (14), 이러한차이는본연구에포함된환자의수가적은것과관련이있을수있다. 보고자에따라피라미드엽의빈도가다른것은피라미드엽의정의에있어서의차이가주된원인일것이라생각되며, 본연구에서는장경이 9 mm 이하인경우는포함되지않았다. 저자들이조사한바로는수술소견을기준으로하여경부전산화단층촬영의피라미드엽의발견에대한진단정확도를산출한연구는없었으며, 수술소견을기준으로한본연구에서는 82.6% 의진단정확도를보였다. 본연구에서비교적높은위양성및위음성률을보였는데, 이는크기 ( 특히, 전후직경 ) 가작은피라미드엽의경우는경부전산화단층촬영에서작은혈관과의구별이어렵기때문일것이다. 또한, 전산화단층촬영에서측정된항목중전후직경, 위치, 상연, 그리고주갑상선과의분리여부에있어서는수술결과와서로차이가있음이확인되었다. 이러한차이의원인은전후직경에서는측정오차일가능성이높으며, 위치는전산화단층촬영과수술시목의자세에있어서의작은차이때문일수있겠다. 피라미드엽의상연은일반적인갑상선수술을통해서는설골수준이상을잘관찰하지못하기때문에전산화단층촬영에서보다낮은수준의피라미드엽만관찰된것으로생각되나, 주갑상선과의분리여부의차이는증례수가너무작아큰의미는없을것으로생각된다. 본연구의제한점은다음과같다. 첫째, 본연구에포함된환자군의수가적었다. 둘째, 한명의영상의학과전문의에의해경부전산화단층촬영이분석되었다. 따라서여러명의연구자가참여하고환자군의수가많은다기관연구가필요할수있다. 셋째, 본연구에서는 3 mm 두께슬라이스의경부전산화단층촬영기법이사용되었으나보다작은슬라이스두께를사용한다면좀더정확한관찰이가능할수도있다. 더욱이조영증강관상면재구성영상은연구에포함되었으나조영증강시상면재구성영상이연구에이용되지않았다. 마지막으로, 환자군의대다수가갑상선암으로수술을받았기때문에일반인을대표하지는못할수있다. 결론적으로, 갑상선피라미드엽에대한경부전산화단층촬영은비교적높은진단정확성을보이며, 설골수준이상의평가에유용할수있다. 참고문헌 1. Moon WJ, Baek JH, Jung SL, Kim DW, Kim EK, Kim JY, et al. Ultrasonography and the ultrasound-based management of thyroid nodules: consensus statement and recommendations. Korean J Radiol 2011;12:1-14 2. Hay ID, Thompson GB, Grant CS, Bergstralh EJ, Dvorak CE, Gorman CA, et al. Papillary thyroid carcinoma managed at the Mayo Clinic during six decades (1940-1999): temporal trends in initial therapy and long-term outcome in 2444 consecutively treated patients. World J Surg 2002;26:879-885 3. Mazzaferri EL, Kloos RT. Clinical review 128: Current approaches to primary therapy for papillary and follicular thyroid cancer. J Clin Endocrinol Metab 2001;86:1447-1463 4. Pacini F. Follow-up of differentiated thyroid cancer. Eur J Nucl Med Mol Imaging 2002;29 Suppl 2:S492-S496 5. Hollinshead WH. Anatomy for surgeons, vol 2. The head and the neck. NewYork: Hoeber-Harper, 1961:517-531 6. Ranade AV, Rai R, Pai MM, Nayak SR, Prakash, Krisnamurthy A, et al. Anatomical variations of the thyroid gland: possible surgical implications. Singapore Med J 2008;49: 831-834 7. Joshi SD, Joshi SS, Daimi SR, Athavale SA. The thyroid gland and its variations: a cadaveric study. Folia Morphol (Warsz) 2010;69:47-50 8. Park JY, Kim DW, Park JS, Kang T, Kim YW. The prevalence and features of thyroid pyramidal lobes as assessed by computed tomography. Thyroid 2012;22:173-177 9. Kim DW, Jung SL, Baek JH, Kim J, Ryu JH, Na DG, et al. The prevalence and features of thyroid pyramidal lobe, accessory thyroid, and ectopic thyroid as assessed by computed tomography: a multicenter study. Thyroid 2013;23:84-91 10. Andersen PE, Kinsella J, Loree TR, Shaha AR, Shah JP. Differentiated carcinoma of the thyroid with extrathyroidal extension. Am J Surg 1995;170:467-470 11. Tsang RW, Brierley JD, Simpson WJ, Panzarella T, Gospodarowicz MK, Sutcliffe SB. The effects of surgery, radioiodine, and external radiation therapy on the clinical outcome of patients with differentiated thyroid carcinoma. Cancer 1998;82:375-388 12. Pacini F, Schlumberger M, Harmer C, Berg GG, Cohen O, 272 대한영상의학회지 2013;69(4):269-273 jksronline.org
신기원외 Duntas L, et al. Post-surgical use of radioiodine (131I) in patients with papillary and follicular thyroid cancer and the issue of remnant ablation: a consensus report. Eur J Endocrinol 2005;153:651-659 13. Moore KL, Persaud TVN. The developing human: clinically oriented embryology. Philadelphia: WB Saunders Company, 1993:200-203 14. Won HS, Chung IH. Morphologic variations of the thyroid gland in Korean adults. Korean J Phys Anthropol 2002;15: 119-125 신기원 김동욱 목적 : 갑상선피라미드엽은정상변이로아직까지이에관한영상의학적연구는적다. 본연구의목적은경부전산화단층촬영에서피라미드엽의빈도, 위치, 크기 ( 길이, 최대전후직경, 최대횡경 ), 상연및주갑상선과의분리여부를확인하고이를수술과정에서확인한것과비교하여이를통해피라미드엽의평가에있어서경부전산화단층촬영의정확성에대해서알아보는것이다. 대상과방법 : 갑상선수술전경부전산화단층촬영을받았던 46명을대상으로하였다. 한명의영상의학과전문의가피라미드엽의경부전산화단층촬영에서의빈도, 위치, 크기, 상연및주갑상선과의분리여부를조사하였다. 결과 : 46명을대상으로피라미드엽의발견에있어서전산화단층촬영의민감도, 특이도, 양성예측도, 음성예측도및정확도는 77.8%, 89.5%, 91.3%, 73.9% 및 82.6% 였다. 피라미드엽의전후직경, 위치, 상연, 주갑상선과의분리여부에있어서는전산화단층촬영과수술결과가서로유의한차이를보였으나 (p < 0.05), 피라미드엽의길이와횡경에있어서는차이를보이지않았다 (p > 0.05). 결론 : 갑상선피라미드엽에대한경부전산화단층촬영은비교적높은진단정확성을보이며, 설골수준이상의평가에유용할수있다. 인제대학교의과대학부산백병원영상의학과학교실 jksronline.org 대한영상의학회지 2013;69(4):269-273 273