This is not caput medusa. This is collateral circulation. Caput medusa is varicose periumbilical veins. This veins are going from lower abdomen to upper abdomen
In a relatively skiny person, we can see the tortuosity of the veins extending all the way to the umblicus ( like in the image u posted ) and in an obese patient the fat distribution becomes more pronounced as we get closer to the umblicus and hence the tortuosity appears to fade. Additionally the more larger or distended the abdomen is - the more parallel (than radiating) the veins seem to each other as we move away from the umblicus thereby giving the impression of collateral circulation.
Thanks so much, friend Neo_Star. I have never heard such an accurate explanation, just wow, excellent!!