How does pyelonephritis affect the renal pelvis?

Bad effects on it: Acute pyelonephritis is an infection of the renal pelvis (collecting system) and the kidney as a whole. There can be kidney abscesses (suppurative necrosis), containing pus material. Kidney tubules are damaged by the infectious process, and may have "casts" of white blood cells and exudate. In the early stages, kidney glomeruli are not affected, but can get damaged if the infection continues.

Pyelonephritis: Although pyelonephritis may affect all areas of the renal parenchyma, the question addresses the pelvis. One can get papillary necrosis with some of the necrotic papillae breaking off and either obstructing the pelvis, or fragments (micro or macro) of material may appear in the urine. Radiologically there may be classic calyceal deformities seen. This usually involves both kidneys.