There may be obstructions due to congenital atresia or to various diseases and neoplasms. The result of such a condition is a dilatation of the ureter above the obstruction and of the kidney (hydronephrosis).

Pyelitis, or inflammation of the pelvis of the kidney, is met with in the course of various infectious diseases, as typhoid fever, scarlet fever, smallpox. In such cases is seldom of any severity. The most important causes are local infection and calculi. Infection may take place through the presence of pyogenic organisms within the urinary apparatus, and according to the degree of severity the inflammation may be catarrhal, hemorrhagic, suppurative, pseudo-membranous, or ulcerative. In the suppurative form there is nearly always an involvement of the renal tissue, a pyelonephritis. If the ulcerated form is severe, perforation may take place and the purulent contents escape into the surrounding tissue, giving rise to a perinephritic abscess, the pus collecting in the areolar and fatty tissue about the kidney. It may remain encapsulated, and compress the kidney, or it may burrow through the deeper tissues and discharge below Poupart's ligament.

In chronic pyelitis the mucous membrane may become much thickened, contain ulcerations, and be covered in places by a precipitation of the salts from the urine. The kidney in this form is often the seat of chronic inflammation, suppuration, or atrophy.

If the ureter becomes obstructed, the pelvis of the kidney may be rilled with pus, a pyonephrosis.

Tuberculosis of the ureter occurs as a rule secondarily to tuberculosis of the kidney, but it may have followed similar disease of the lower portion of the urinary tract.

Fig. 171. - Tuberculous Nodule in the Wall of the Ureter, with Beginning Hydronephrosis (from a specimen in the Museum of the Philadelphia Hospital, Phila.).

Calculi may lodge within the ureter and give rise to varying disturbances, from acute renal colic to obstruction with subsequent hydronephrosis. Hemorrhage may be caused by laceration of the mucous membrane and suppuration is not uncommon.

Parasites at times find their way into the ureters and pass up to the kidney.