Anatomical variant of large mediastinal veins Incidental findings on MDCT chest The Egyptian Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx Contents lists available at ScienceDirect The[.]
The Egyptian Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx Contents lists available at ScienceDirect The Egyptian Journal of Radiology and Nuclear Medicine journal homepage: www.sciencedirect.com/locate/ejrnm Review Anatomical variant of large mediastinal veins: Incidental findings on MDCT chest Tamer F Taha Ali a,⇑, Abdel-Naser Ghareep b a b Department of Radiodiagnosis, Faculty of Medicine, Zagazig University, Egypt Department of Radiodiagnosis, Faculty of Medicine, Al-Azhar University, Egypt a r t i c l e i n f o Article history: Received 17 October 2016 Accepted 28 November 2016 Available online xxxx Keywords: Chest Venous MDCT Congenital a b s t r a c t Thoracic veins congenital abnormalities are important uncommon developmental anomalies that have a wide range of presentation from isolated incidental findings to a part of more complex anomalies It can be categorized into systemic venous system and pulmonary venous system It is of important value to understand the mediastinal vascular anatomy to help to identify variable vascular anomalies In this study we attempt to describe some incidentally encountered mediastinal large venous anatomical variants in patients undergoing MDCT chest in order to avoid further unnecessary studies Ó 2016 The Egyptian Society of Radiology and Nuclear Medicine Production and hosting by Elsevier This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/) Contents Introduction The superior vena cava (SVC) Azygos vein Pulmonary veins 4.1 Partial anomalous pulmonary venous return (PAPVR) 4.2 Total anomalous pulmonary venous drainage (TAPVR) Pulmonary varix Conclusion Conflict of interest References Introduction Thoracic veins congenital abnormalities are not common, however they are considered as important developmental anomalies Congenital anomalies of thoracic venous system has a wide range of presentation from isolated incidental findings during lung or cardiac imaging to a part of a more complex anomalies especially associated with congenital cardiac diseases [1–4] Venous congen- Peer review under responsibility of The Egyptian Society of Radiology and Nuclear Medicine ⇑ Corresponding author E-mail address: tamerfathi2008@yahoo.com (T.F Taha Ali) 00 00 00 00 00 00 00 00 00 00 ital anomalies can be categorized into systemic venous system (including SVC and the Azygos system) and pulmonary venous system [2,4,5–8] Systemic venous abnormalities are frequent incidental findings, while the pulmonary venous abnormalities are usually manifested with cyanosis due to abnormal blood flow and associated pulmonary venous flow obstruction in some cases [1,2] It is of important value to understand the mediastinal vascular anatomy to help to identify variable vascular anomalies During study interpretation, radiologist should not only consider the various anatomic variants but also to have knowledge of their different classifications, associated anomalies and clinical presentation Proper rule out of these anomalies especially when encountered http://dx.doi.org/10.1016/j.ejrnm.2016.11.011 0378-603X/Ó 2016 The Egyptian Society of Radiology and Nuclear Medicine Production and hosting by Elsevier This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Taha Ali TF, Ghareep A-N Egypt J Radiol Nucl Med (2016), http://dx.doi.org/10.1016/j.ejrnm.2016.11.011 T.F Taha Ali, A.-N Ghareep / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx incidentally has a significant implication on avoiding additional non necessary examinations especially in case of simulation of thoracic disease [2–4] The superior vena cava (SVC) The superior vena cava (SVC) is the largest systemic mediastinal vein It is formed at the right side of superior mediastinum at the level of first costal cartilage by the union of the bilateral (right and left brachiocephalic veins) It runs in caudal direction to end in the right atrium (sinus venosus portion) [9,10] During embryological life, there are right and left anterior cardinal as well as common cardinal veins Normally, the SVC is formed from the right anterior cardinal and common cardinal veins regression of the left anterior cardinal vein occurs [9–12] Concurrent non-regression of the left anterior cardinal vein leads to occurrence of double SVC while if persistent left anterior cardinal vein with regression of the right cardinal vein results in solitary left SVC [9–12] The left SVC has lateral relation to the aortic arch and anterior relation to the left pulmonary hilum, it runs inferiorly to enter the pericardium and finally drain into the coronary sinus [2,11,13] (Fig 1) The accurate incidence of persistent left SVC is difficult to establish Many previous reports showed that 0.1–0.5% is the average prevalence of incidental finding of left SVC in the general population while this prevalence is higher in congenital cardiac disease patients reaching up to 2.1 and 5% [2,12–17] The left SVC is found to be a part of a duplicated SVC in most cases In duplicated SVC, the right SVC is smaller than left in most cases as well as absent left brachiocephalic vein is notable [11,13] (Fig 2) A left SVC is usually asymptomatic incidental finding with no hemodynamic significant effect [11] However, it is of important implications when using the left brachiocephalic the pulmonary vasculature or right heart is accessed through the left subclavian vein The presence of LT side SVC can make some procedures like Swan-Ganz catheter placement, placement of pacemaker or implantable defibrillator difficult [3,18] On radiographs, absence of right SVC can results in the prominence of the ascending aorta which may simulate an abnormal aorta A left SVC can results in left side focal superior mediastinal widening at the aortic knob [3,18,19] Azygos vein Embryologically azygos vein is formed from the right posterior cardinal vein (inferiorly) and the right supracardinal veins (superiorly), while the left supracardinal vein forms the hemiazygos and accessory hemiazygos veins [20–22] The azygos vein is formed mostly at 12th vertebra by the union of the ascending lumbar and right subcostal veins It enters the chest via the aortic hiatus or postero-lateral to the right crus It ascends in the posterior mediastinum before arching over the right main bronchus at the level of T5-T6 to join SVC [21–26] The hemiazygos vein is formed by the union of the left ascending lumbar and subcostal veins It passes through the aortic hiatus or the diaphragmatic crura It ascends on the left aspect of dorsal vertebrae then crosses the midline to join the azygos vein at the level of 8th or 9th dorsal vertebrae [20–22] In extremely uncommon circumstances the azygos vein is absent and this can be a result of failure of the development of the superior segment of the right supracardinal vein It is usually symptom-free as the hemiazygos and accessory hemiazygos veins Fig CT axial images (a–c) shows single LT sided SVC (L) anterior to the left hilum CT volume rendering image (d) shows single LT sided SVC (L) draining into coronary sinus Please cite this article in press as: Taha Ali TF, Ghareep A-N Egypt J Radiol Nucl Med (2016), http://dx.doi.org/10.1016/j.ejrnm.2016.11.011 T.F Taha Ali, A.-N Ghareep / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx its arterial and bronchial supplies arise from the right upper lobe (apical or posterior segments) [22,25,26] (Fig 3) Failure of anastomosis of the right subcardinal vein (precursor of pre-renal IVC) with the hepatic vein during embryogenesis will result in interrupted IVC with azygos or hemiazygos continuation Blood returns to the heart from the post renal neonatal circulation through the supracardinal veins (precursor of azygos and hemiazygos veins) [22–26] In patients with hemiazygos continuation of left sided IVC, blood drains from hemiazygos through azygos or accessory azygos to persistent left SVC or from hemiazygos to superior intercostal veins into normal right sided SVC [22–26] (Fig 4) Fig CT axial images (a and b) Double SVC Right SVC (R) and Left SVC (L) CT coronal reformatted image (c) showing double SVC Right SVC (R) draining into the right atrium and Left SVC (L) draining into coronary sinus will drain the right and left intercostal veins with consequent enlargement [23] The azygos lobe is a normal variant Its incidence on chest X-ray is about 0.4–1% It is formed by penetration of the right posterior cardinal vein to the right lung apex instead of migration over it with two pleural layers that invaginates into the upper portion of upper lobe of right lung [25,26] It is not a true accessory lobe as Fig Azygos fissure CT axial (a) and coronal reformatted images (b and c) shows azygos lobe bounded laterally by azygos arch Please cite this article in press as: Taha Ali TF, Ghareep A-N Egypt J Radiol Nucl Med (2016), http://dx.doi.org/10.1016/j.ejrnm.2016.11.011 T.F Taha Ali, A.-N Ghareep / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx Fig CT axial (a–c), coronal reformatted (d) images showing dilated hemiazygos draining into LT SVC with polysplenia (e: axial CT upper abdomen image) CT axial (a–c), coronal reformatted (d) showing dilated hemiazygos draining into LT SVC with polysplenia (e: CT upper abdomen image) The frequency of azygos continuation is around 0.6% [23] It is more common in patient with polysplenia It is important to identify the azygos anomalies before cardiac catheterisation and interventional procedures such as balloon dilatation or stent and umbrella placement as well as before some surgical interference such as procedures needing azygos ligation [22–26] On chest radiograph azygos continuation can result in right paratracheal stripe focal widening just above the main stem of right bronchus [23–25] Pulmonary veins The superior pulmonary veins drain the upper and middle lobes of the right lung and the upper lobe and lingua of the left lung while the lower lung lobes drain through right and left inferior pulmonary veins At the hilar region, the superior pulmonary veins are located anterior and caudal to the pulmonary arteries while inferior pulmonary vein ostea are more dorsal and medial location Finally the four pulmonary veins drain into the left atrium [27] (Fig 5) Please cite this article in press as: Taha Ali TF, Ghareep A-N Egypt J Radiol Nucl Med (2016), http://dx.doi.org/10.1016/j.ejrnm.2016.11.011 T.F Taha Ali, A.-N Ghareep / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx Embrylogically, the lung buds are derived from the foregut and drained via vascular plexus that has connection to cardinal veins and further to systemic venous system With further development the common pulmonary vein is formed and become connected to the vascular plexus while the connections with the cardinal vein obliterates Failure of obliteration of these connections results in either partial or complete pulmonary venous return anomalous [3,27–33] 4.1 Partial anomalous pulmonary venous return (PAPVR) The overall incidence of partial anomalous pulmonary venous return (PAPVR) is about 0.5–0.7% In this anomaly draining of blood from anomalous pulmonary vein into the systemic circulation establish a right to left shunt [34–40] The abnormal vein can drain into any of the following structures [10,34]: Right Upper lobe: Usually drains into the SVC, it is considered the most common type of PAPVR and is associated with atrial septal defect of sinus venosus type Right lower lobe: usually drains into inferior vena cava (IVC), portal or hepatic veins This can be isolated finding or associated with pulmonary hypoplasia (Scimitar syndrome) (Fig 6) Left upper lobe: 2nd most common type of PAPVR Drains into the brachiocephalic vein (isolated finding) Left lower lobe: This is a rare entity An anomalous vein (scimitar vein) drains a part or total lung into the IVC either above or below the diaphragm or can drain into hepatic, portal or azygos vein or even to coronary sinus or right atrium The right lung is nearly exclusively affected The Scimitar syndrome is characterized also by hypoplasia of the right lung and right pulmonary artery with abnormal systemic arterial supply to right lung This abnormal vein has been described as a ‘‘Scimitar” as it is resemble the Middle Eastern sword A single anomalous vein usually has insignificant hemodynamic effect; however the pulmonary hypoplasia with complicated pulmonary hypertension and chest infections affects the severity of symptoms [10,35] Fig CT axial (a) & coronal (b): showing Scimitar vein (S) draining into IVC 4.2 Total anomalous pulmonary venous drainage (TAPVR) Total anomalous pulmonary venous drainage (TAPVR) is categorized according to the route of venous drainage into types [10] Type I: supracardiac (most common form), drainage to the left brachiocephalic, right SVC or azygos vein Type II intracardiac drainage to the coronary sinus or right atrium, Type III infracardiac drainage to the portal, ductus venosus or right atrium, or mixed type Patient are usually presented in the neonatal period as the presence of an obligatory ASD or patent foramen ovale establish a right to left shunt and cyanosis Fig CT volume rendering Normal pulmonary vein drain into right atrium (RA) Fig CT axial (a) & coronal reformatted (b); pulmonary varix (V) Please cite this article in press as: Taha Ali TF, Ghareep A-N Egypt J Radiol Nucl Med (2016), http://dx.doi.org/10.1016/j.ejrnm.2016.11.011 T.F Taha Ali, A.-N Ghareep / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx Pulmonary varix Pulmonary varix is rare condition characterized by focal enlargement of segmental pulmonary veins It is usually asymptomatic and may be mistaken as lung nodule or mediastinal masses at radiographs 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A multiplane transoesophageal approach Heart 2002;88:634–8 [39] Ibrahim M, Burwash IG, Morton B, Brais M Direct drainage of the right pulmonary into the coronary sinus with intact interatrial septum: a case report Can J Cardiol 2001;17:807–9 [40] Frydrychowicz A, Landgraf B, Wieben O, Franỗois CJ Scimitar syndrome Circulation 2010;121:e4346 [41] Minniti S, Visentini S, Procacci C Congenital anomalies of venae cavae Eur Radiol 2002;12:2040–55 [42] Vanherreweghe E, Rigauts H, Bogaerts Y, Meeus L Pulmonary vein varix: diagnosis with multislice helical CT Eur Radiol 2010;10:1315–7 Please cite this article in press as: Taha Ali TF, Ghareep A-N Egypt J Radiol Nucl Med (2016), http://dx.doi.org/10.1016/j.ejrnm.2016.11.011 ... or mediastinal masses at radiographs [4,41,42] (Fig 7) Conclusion Mediastinal venous vascular anatomical variants can be incidental findings on imaging studies including CT Knowledge of these variants... development the common pulmonary vein is formed and become connected to the vascular plexus while the connections with the cardinal vein obliterates Failure of obliteration of these connections results... Journal of Radiology and Nuclear Medicine xxx (2016) xxx–xxx incidentally has a significant implication on avoiding additional non necessary examinations especially in case of simulation of thoracic