The portal venous system develops between the 4th and 10th weeks of gestation. During the 4th week, two vitelline veins emerge from the anterior portion of the yolk sac, connecting to and draining into the sinus venosus (Papamichail et al. 2018). Within the septum transversum, vitelline plexuses develop that connect to the vitelline veins, creating a network of veins that surround the primitive liver, later becoming hepatic sinusoids (Schoenwolf et al. 2020). By the end of the third month of development the left vitelline vein has regressed, causing blood from the left side of the abdominal viscera to drain to the right vitelline vein via transverse anastomoses (Schoenwolf et al. 2020). The portion of the right vitelline vein that remains, just caudal to the liver, becomes the portal vein and superior mesenteric vein (Schoenwolf et al. 2020). Left-to-right remodeling of the vitelline anastomoses leads to the formation of the inferior mesenteric vein (IMV), draining the embryo’s hindgut (Schoenwolf et al. 2020).