In case of IVC obstruction, the collateral which opens up are all except -
Whenever there is an obstruction in superior or inferior vena cava, collateral circulation opens up to connect inferior vena cava and superior vena cava. This helps in circulation being maintained by draining into the right atrium. The veins that can form collaterals include
-        Superior epigastric
-        Internal thoracic
-        Lateral thoracic
-        thoracoepigastric
-        Posterior intercostal
-        Lumbovertebral
-        Superficial epigastric
-        Superficial circumflex iliac
-        Deep circumflex iliac
-        Inferior epigastric
-        External pudendal
-        Azygous
-        Hemizygous
-        Ascending lumbar
Superior epigastric & inferior epigastric vein
Azygos & ascending lumbar vein
Superficial epigastric & ileolumbar vein
Lateral thoracic veins & prevertebral vein