Original Article pISSN 1738-2637 / eISSN 2288-2928 J Korean Soc Radiol 2017;76(4):264-272 https://doi.org/10.3348/jksr.2017.76.4.264 True Tracheal Bronchus: Classification and Anatomical Relationship on Multi-Detector Computed Tomography 참기관기관지: Multi-Detector Computed Tomography를 이용한 분류 및 해부학적 관계 Hyunjeong Kim, MD, Young Tong Kim, MD*, Sung Shick Jou, MD, Woong Hee Lee, MD Department of Radiology, Soonchunhyang University Cheonan Hospital, Soonchunhyang University College of Medicine, Cheonan, Korea Purpose: To propose the imaging classification of true tracheal bronchus (TTB) on Index terms multi-detector computed tomography (MDCT), and to evaluate its anatomical relation- Multidetector Computed Tomography ship with surrounding structures. Bronchus Materials and Methods: This study included 44 patients who were diagnosed with Congenital Abnormalities TTB on MDCT for 6 years. We classified TTB into five types, based on the existence of Classification the right upper lobe bronchus originating from the right main bronchus and the num- ber of segmental bronchi of TTB. We analyzed the site of origin and the running direc- Received June 1, 2016 tion of TTB based on its anatomical relationship with surrounding structures and some Revised August 17, 2016 ancillary findings. Accepted September 6, 2016 Results: The imaging classification of TTB included Type I (47.7%), Type II (13.6%), Type *Corresponding author: Young Tong Kim, MD Department of Radiology, Soonchunhyang University III (11.4%), Type IV (25.0%), and Type V (2.0%). According to the site of origin of TTB, be- Cheonan Hospital, Soonchunhyang University College low the aortic arch (52.3%) and at the level of the aortic arch (43.1%) were the two of Medicine, 31 Suncheonhyang 6-gil, Dongnam-gu, main sites of origin, whereas the frequency of the site of origin above the azygos arch, Cheonan 31151, Korea. Tel. 82-41-570-3515 Fax. 82-41-579-9026 at the level of the azygos arch, and below the azygos arch was 27.3%, 38.6%, and E-mail: [email protected] 34.1%, respectively. Considering both aortic and azygos arches, below the aortic arch and below the azygos arch were the most common sites of origin (27.3%). With respect This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial to the running direction of TTB, in all cases, TTB passed below the azygos arch to the License (http://creativecommons.org/licenses/by-nc/4.0) right upper lobe. There was no statistically significant p( > 0.05) difference in age or sex which permits unrestricted non-commercial use, distri- between types of TTB. Ancillary findings included tracheal stenosis n( = 2), narrowing of bution, and reproduction in any medium, provided the original work is properly cited. the right main bronchus (n = 2), luminal narrowing of TTB and bronchiectasis at the distal portion (n = 1), and a highly located azygos arch above the aortic arch (n = 2). Conclusion: The proposed imaging classification of TTB and its anatomical relation- ship with surrounding structures will improve our understanding of various imaging features and embryological development of TTB. Radiologists should pay careful at- tention to evaluation of the airway including the trachea on thoracic imaging. INTRODUCTION The incidence of tracheal bronchus has been reported to range from 0.001% to 2% based on a bronchoscopy, autopsy, or radio- Tracheal bronchus is a congenital anomaly of bronchial divi- logical study. Tracheal bronchus may also be associated with oth- sion. A variety of bronchial anomalies originate from the tra- er congenital anomalies such as Down’s syndrome and congeni- chea or main bronchus and are directed to the upper lobe terri- tal heart disease (5). Pig bronchus is an anomaly of the entire tory (1). Tracheal bronchus usually originates from the main right upper lobe bronchus arising from the trachea. Tracheal bronchus or trachea within 2 cm from the carina, and it supplies bronchus can be divided into displaced type or supernumerary the entire upper lobe or apical segment of the upper lobe (2-4). type, with the displaced type being more frequent than the super- 264 Copyrights © 2017 The Korean Society of Radiology Hyunjeong Kim, et al numerary type. The supernumerary bronchi may end blindly. to a slice thickness of 1.25 mm and an interval of 1.25 mm. Using They are called tracheal diverticulum (1-8). In tracheal bron- three-dimensional image analysis program (Portal workstation chus, an anomaly that originates only from the trachea is called V2.6.0.32, Philips Medical Systems), we acquired coronal views, true tracheal bronchus (TTB), which has a great clinical signifi- minimum intensity projection, and three- dimensional volume cance. It can be easily confirmed by surgery or bronchoscopy rendering (VR) images. CT images were reviewed by two radi- (2). Therefore in this study, we only focused on TTB. ologists (K.Y.T and K.H.J) with 26 and 3 years of experience in Recently, CT findings of TTB have been studied using multi- interpreting thoracic CT in consensus. We did not formally as- detector computed tomography (MDCT) with multiplanar re- sess interobserver agreement. construction and three-dimensional images (3, 5, 8, 9). Most ar- In this article, TTB was defined as an anomalous bronchus ticles on CT findings of TTB have focused on its incidence, arising from the trachea and directed to the right upper lobe. classification, or accompanying anomalies. To the best of our TTB was classified by analyzing axial, coronal and minimum knowledge, studies illustrating the anatomical relationship be- intensity projection images, multi-planar reformation images, tween TTB and the surrounding structures have been rarely re- and VR images. We classified TTB into five types (Type I to ported (3, 6, 9). Therefore, the purpose of this study was to clas- Type V) according to the existence of right upper lobe bronchus sify TTB radiologically using multiplanar reconstruction and originating from the right main bronchus and the number of three-dimensional images obtained by MDCT and to evaluate branches of segmental bronchus originating from TTB (Fig. 1). the anatomical relationship between TTB and the surrounding We evaluated the sites of origin and running directions of structures. Because it is difficult to perform precise differentia- TTB based on its anatomical relationship with surrounding tion of displaced type or supernumerary type at the lung pe- structures. The sites of origin of TTB were classified as follows: riphery only by CT, we tried a new subspecialized classification Type I (n = 21) Type II (n = 6) of TTB according to the existence of right upper lobe bronchus originating from the right main bronchus, and the number of segmental bronchi originating from the trachea in this study. MATERIALS AND METHODS This retrospective study was approved by the Institutional Re- Type III (n = 5) Type IV (n = 11) Type V (n = 1) view Board of our hospital. The requirement for obtaining in- formed patient consent was waived. Patients This study included 44 patients (2–80 years old, 24 males and 20 females; mean age of 51.3 years) who underwent MDCT ex- Fig. 1. Imaging classification of true tracheal bronchus on MDCT. amination between January 2010 and August 2015 at a single Type I: Anomalous one segmental bronchus arising from the lower trachea to the right upper lobe with existence of the right upper lobe tertiary center in Korea. bronchus originating from the main bronchus. Type II: Anomalous two segmental bronchi arising from the lower trachea to the right up- per lobe with existence of the right upper lobe bronchus originating CT Analysis from the main bronchus. Type III: The entire right upper lobe bron- All chest CTs were performed with a 64-channel multidetec- chus arising from the lower trachea without existence of the right up- per lobe bronchus arising from the main bronchus. Type IV: Anoma- tor scanner (LightSpeed VCT; GE Medical Systems, Milwau- lous bronchus arising from the lower trachea with a blind end. Type V: kee, WI, USA) and a 256-channel multidetector scanner (Bril- Anomalous segmental bronchus arising from the lower trachea to the right upper lobe without existence of the right upper lobe bronchus liance iCT; Philips Medical Systems, Cleveland, OH, USA). CT arising from the main bronchus. images were restored as DICOM files after being reconstructed MDCT = multi-detector computed tomography jksronline.org J Korean Soc Radiol 2017;76(4):264-272 265 True Tracheal Bronchus above the aortic arch, at the level of the aortic arch, below the and the surrounding structures. However, we were able to ana- aortic arch, above the azygos arch, at the level of azygos arch, and lyze the relationship with gender and age. We used Fisher exact below the azygos arch. The associations between the types of test for gender and Kruskal-Wallis test for age. Statistical signif- TTB and gender, age, or the anatomical relationships were de- icance was attained when p value was less than 0.05. Type 5 was termined. We also reviewed ancillary findings such as changes excluded from the statistical analysis because there was only in the diameter of the trachea and main bronchus. one such case. Statistical Analysis RESULTS The patient group for each type was too small to perform a sta- tistical analysis of the anatomical relationship between each type Based on the imaging classification of TTB, Type I occurred A B C Fig. 2. True tracheal bronchus (Type I) in an asymptomatic 35-year-old man. A. Axial CT image showing a highly located azygos arch (arrowhead) at the level of site of origin of thoracic great vessels. B, C. Axial CT (B) and coronal minimum intensity projection (C) images showing true tracheal bronchus (open arrow) originating at the level of the azygos arch and running below the azygos arch.