Cavernous transformation describes the perihilar vascular sequelae of a portal vein thrombus, which may develop as soon as 6-20 days after the acute thrombotic event. The new collateral vessels may be porto-systemic in nature (ie. via left gastric or perisplenic veins) or porto-portal (ie. formation of new intrahepatic branches).
For an interesting look at the hemodynamics of cavernous transformations, check out the link to this 1995 article in Am J Roentgenol.