The two types of pyelosinus extravasation

There are two types of extravasation into the renal sinus from the fornices of the calyces; one due to transudation through an intact mucosa and the other due to an actual defect in the calyx. It is suggested that extravasation from the fornices into the renal sinus can occur spontaneously in the absence of obstruction and without a rise in pressure. Truly spontaneous extravasation can occur whether ureteric compression is used or not.