In IVC obstruction, all of the following collaterals help EXCEPT:

In IVC obstruction, collaterals open up to drain blood into SVC and then to the hea (right atrium). Since, superficial epigastric and iliolumbar vein both drain into IVC, they are not helping the cause. Superior epigastric and inferior epigastric form collateral in rectus sheath. Superior epigastric drain into internal thoracic then into SVC which open into right atrium, hence blood can be drained from IVC into SVC . Superficial Epigastric vein forms collaterals with Lateral Thoracic vein thoracoepigastric vein in case of either IVC or SVC obstruction