Renal pelvis is the funnel-shaped proximal part of ureter that gathers urine from collecting ducts and passes it on to the ureter (image A) & (image B).
Image C (click on the image above)
Image D (click on the image above)
Similar to the bladder, the pelvis and ureter are lined by urothelium, which consists of umbrella, intermediate and basal cells.
About 2-3 minor calyxes converge into a major calyx, and 2-3 major calyxes converged into the renal pelvis.
Both renal pelvis and ureters contain smooth muscles (muscularis propria) that contracts to force urine from kidney to bladder.
Ureter has a "star-shaped" lumen surrounded by 2 layers of smooth muscle for the proximal 2/3 of its length, and 3 layers of muscle for the final 1/3 of its length to the bladder (image C) & (image D).
Carcinoma from renal pelvis or ureter is staged based on the level of underlying structural invasion.
Non-invasive carcinoma from the pelvis may travel within the collecting duct without renal parenchymal invasion.
Not staged pathologically as kidney invasion (remains carcinoma in situ or not as pT3!).