the left innominate vein usually courses anterior or anterosuperior to the aortic arch to join the right innominate vein , forming the superior vena cava ( svc ) . however , retroaortic course is reported in around 0.2 - 1% of patients with congenital cardiac anomalies such as tetralogy of fallot and right ventricular outflow obstruction . isolated retroaortic innominate vein in situs solitus without cardiac or aortic anomalies is extremely rare with very few reports in literature . contrast - enhanced computed tomography ( ct ) scan of thorax , abdomen , and pelvis was done in dual - energy ct scanner ( somatom definition flash , siemens healthcare , erlangen , germany ) to rule out any underlying neoplasm . incidentally , the left innominate vein had an abnormal course [ figure 1 ] behind the ascending aorta before joining the right innominate vein to form the svc which was normal in position ( on the right side ) . the volume - rendered three - dimensional images obtained by dual - energy based bone removal clearly showed the relationship with the aortic arch [ figure 2 ] . the anomalous course of the retroaortic innominate vein was highlighted in the report because of its clinical implications . ( a , b ) axial and ( c ) coronal post - contrast computed tomography ( ct ) section showing the retroaortic course of left innominate vein ( arrow ) ( a and b ) volume - rendered three - dimensional reconstruction showing the retroaortic course of the left innominate vein ( arrow ) . retroaortic innominate or brachiocephalic vein is an uncommon variant , first described 125 years ago by kershner . it is usually reported in patients with congenital heart diseases , with a reported incidence of 0.2 - 1% . common association is tetralogy of fallot with right aortic arch , with or without pulmonary atresia . chen et al . reported 27 cases of anomalous retroaortic vein on routine scanning of patients with congenital heart disease during a period of 8 years . even after increasing use of cross - sectional imaging , incidental detection of this anomaly only few reports of isolated anomalous innominate vein without cardiac anomalies and with normal left aortic arch exist in literature . nagashima et al . reported only one patient with anomalous vein out of 4805 patients ( without congenital heart disease ) who underwent cardiac surgeries . primitive venous system consists of paired precardinal and postcardinal veins which join to form the common cardinal vein . right common cardinal vein develops into the svc in later life ( the left common cardinal vein and most of left anterior cardinal vein usually disappear ) . the venous channels of the left side of head and neck are directed toward the right precardinal vein through superior and inferior transverse anastomotic channels . normally , the inferior transverse anastomosis which lies beneath the fourth aortic arch regresses and the superior anastomotic channels form the left brachiocephalic vein . presence of high aortic arch and lack of shortening of the aortic arch may exert compression over the superior transverse anastomotic plexus . in such situations , the subaortic space may be widened which facilitates persistence of inferior transverse anastomotic channels that develop into the anomalous innominate or brachiocephalic vein . similarly , pulmonary atresia , hypoplasia , or stenosis also facilitates development of anomalous left brachiocephalic vein . the anomalous retroaortic innominate vein has certain clinical implications , and hence , needs to be highlighted if incidentally detected . on non - contrast axial ct sections , this variant may mimic an enlarged lymph node , although it is easy to appreciate in multiplanar projections . difficulty may be encountered during insertion of central venous catheter through left jugular or subclavian approach . if the surgeon is not aware before surgery , this can be mistaken for absent left brachiocephalic vein after sternotomy . during cardiopulmonary bypass , the cannulation of svc has to be done more caudally as the anomalous vein enters the vena cava more inferior than usual . during surgeries for congenital abnormalities , anomalous innominate vein may obscure the surgical field , causing difficulties in visualization of pulmonary arteries . in conclusion , although extremely rare in isolation , recognition of anomalous left brachiocephalic vein is important for the treating physician before planning any intervention or surgery .
retroaortic innominate vein is an uncommon variant reported in patients with congenital heart disease . however , isolated retroaortic innominate vein without associated cardiac or arch anomalies is extremely rare . 
 we present a case of a 68-year - old man who was found to have this anomalous variant incidentally on computed tomography ( ct ) of the thorax . 
 we also briefly discuss its associations , embryology , and clinical significance .