Need help understanding ct of abdomen... liver: portal vein is patent, retroaortic left renal vein, a normal variant. can it be caused from injuries?

No: This is what we call a 'normal variant' and is of no consequence unless you need surgery on your aorta (such as in the case of an aneurysm). In this situation, it is important that you tell the vascular surgeon that you have this as the left renal vein can be an important landmark during surgery.

Vascular : This is a normal finding. Most left renal veins cross anterior to the aorta. A retrospective vein means it crosses behind the aorta to drain into the inferior vena cava. It is of no clinical significance to you unless you have certain surgeries in the future.

Patent means open : "portal vein patent" means the portal vein (which flows from the GI tract and spleen into the liver) is open and flowing. This does not say which direction it flows- it can reverse with severe liver problems like cirrhosis. But, it means they did not see any clot in it.