Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Access into the portal venous system for interventional procedures has been achieved using a variety of approaches: trans-jugular (by creation of a trans-jugular intrahepatic portosystemic shunt) [4], trans-femoral (through spleno-renal or gastro-renal shunts) [5], trans-hepatic [6–9], trans-splenic [10–24], and percutaneous access through recanalized umbilical vein [25] or abdominal wall varices when available.
Category: