Hydronephrosis (plural: hydronephroses) is defined as dilatation of the urinary collecting system of the kidney (the calyces, the infundibula, and the pelvis) 1.
Hydronephrosis in fetuses and newborns has specific causes that are covered in a separate article.
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Terminology
The term hydroureteronephrosis (or hydronephroureterosis) may be used when the dilatation occurs in the presence of hydroureter.
Radiographic features
Following the identification of hydronephrosis, appropriate further investigations must be undertaken to establish an underlying cause, with potential etiologies including everything from urolithiasis, pelviureteric junction obstruction, malignancy such as cervical cancer, and retroperitoneal fibrosis.
Ultrasound
Ultrasound imaging of hydronephrosis will demonstrate a dilated pelvicalcyceal system. The severity is often classified into mild, moderate or severe hydronephrosis. Thinning of the renal cortex in the context of hydronephrosis usually implies chronicity. Of note, bladder outflow obstruction (or simply a very full bladder) may result in a bilaterally prominent pelvicalyceal system. This can be assessed by rescanning the kidneys post-void to assess for change in the degree of pelvicalyceal dilatation.
CT
CT will readily show hydronephrosis, and can also help identify the cause.
Unenhanced CT is often used to look for urinary tract calculi.
Contrast enhanced CT in the portal venous phase can help to delineate other causes of hydronephrosis, such as retroperitoneal fibrosis and pelvic malignancies.
Delayed phase contrast enhanced CT imaging is useful for intrinsic assessment of the collecting system, and can more clearly demonstrate ureteric strictures or carcinomas, bladder malignancies and non-calcified stones.
Nuclear medicine
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.
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