Hydronephrosis (plural: hydronephroses) is defined as dilatation of the urinary collecting system of the kidney (the calyces, the infundibula, and the pelvis) .
Hydronephrosis in fetuses and newborns has specific causes that are covered in a separate article.
The term hydroureteronephrosis (or hydronephroureterosis) may be used when the dilatation occurs in the presence of hydroureter.
Following the identification of hydronephrosis, appropriate further investigations must be undertaken to establish an underlying cause, with potential etiologies including everything from urolithiasis, UPJ obstruction, malignancy such as cervical cancer and retroperitoneal fibrosis.
A nuclear medicine diuretic renogram may be performed to assess for obstruction of urine and differentiate from other causes such as an extra-renal pelvis or parapelvic cysts.
The radiologist may also play a part in procedures to treat the harmful effects of uncorrected hydronephrosis on renal function, such as placement of a percutaneous nephrostomy tube or antegrade ureteric stent insertion.