Fig. 1
From: Persistent left superior vena cava: clinical importance and differential diagnoses
Developmental stages of primitive venous system and embryology of PLSVC. a In the 5th week of the intrauterine life, there are three paired veins: vitelline veins (VV), umbilical veins (UV), cardinal veins. Right and left superior and inferior cardinal veins ( respectively, RSCV, RICV, LSCV, LICV) combine to form common cardinal veins (CCV) draining into the double horned sinus venosus (SV). The sinus venosus accepts blood, also, from UVs and VVs. Transverse venous canals, called superior and inferior transverse venous plexus (respectively, STVP and ITVP), develop around the primitive aorta and connect RSCV and LSCV. b In the 8th week, the cranial parts of RSCV and LSCV form internal jugular (JV), subclavian (SCV), and brachiocephalic veins. The caudal part of RSCV, together with the right CCV, forms the superior vena cava (SVC). The caudal part of LSCV firstly forms the left superior intercostal vein (LSICV). Then, together with the left CCV, it transforms into the Marshall ligament. RICV forms azygos vein (AzV), and LICV regresses. While the left VV with right and left UV regresses (dashed lines), the right VV forms inferior vena cava (IVC). During this period, the right horn of the sinus venosus joins into the right atrial structure (RA) while the left horn turns into the oblique vein of the left atrium (OV) and the coronary sinus (CS), which drains major cardiac veins. The STVP contributes to the formation of the left brachiocephalic vein (LBCV) while the ITVP regresses (dashed lines) with the compression by the growing aorta and pulmonary artery. c If the STVP regresses (dashed lines) by the highly located aortic arch, such as the right aortic arch, the cervical aortic arch, the ITVP continues to develop and turns into the aberrant left brachiocephalic vein (ALBV). d, e If the left CCV and the caudal part of LSCV do not regress, they will persist as PLSVC. There could be LBCV connecting right SVC (RSVC) and PLSVC, which is also called the bridging vein (d). The STVP, which forms the LBCV, may undergo idiopathic regression (dashed lines) in PLSVC existence, resulting in the absence of the bridging vein (e)