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Duplication of the internal jugular vein is a rare congenital anomaly. Embryologically, the origin of the internal Jugular vein is from the precardial vein. It has been postulated that, duplication may result from derangement from early development between the third and sixth gestational week 6.The common association with Phlebectasia suggests abnormal development of venous wall, possibly involving incomplete formation of the muscular layer.
Three theories have been put forward to explain duplication 2. The vascular theory is the one that is usually accepted 2. This theory suggests that duplication is thought to result from the appearance of a secondary venous ring at a lower level surrounding the spinal accessory nerve. The persistence of this secondary ring adult life may be important in the aetiology of venous duplication2
A bifurcated IJV is one of the many possible manifestations of CCSVI.