Pyelonephritis is an acute inflammatory process of the kidney and its tissues caused by a bacterial infection.

The most common secondary (obstructive) pyelonephritis, develops due to violation of the urine outflow from the kidney. In 85% of cases, it is caused by a stone in the ureter. Various tumor processes can also interfered urinary flow. Sometimes the ureter shrinks during pregnancy as the fetus enlarges.

A kidney cancer is a qualitative change of the organ cells, resulting  the pathological proliferation of its tissues.

Due to the spread of the tumor process, the contralateral kidney, ipsilateral regional lymph nodes, adrenal glands, bones and liver are usually affected.

A kidney cyst is a benign formation, inside of which is a bright clear fluid produced by the walls of the cyst.

Cysts can be single or multiple, develop in one or both of the kidneys. Formation can be congenital, but more often it appears during life. The main version of the cysts origin is an adverse condition for the outflow of urine through the intrarenal urinary ducts.

Hydronephrosis is a gradual atrophy of the kidney  tissues as a result of disturbed outflow of urine and constriction of the pelvic-ureteric junction  (where the kidney pelvis is narrowing and turning into ureter).