- Hydronephrosis refers to a structural finding: dilatation of the renal calyces and pelvis.
- Can be accompanied with hydroureter (dilatation of the ureter)
- Hydronephrosis should not be used interchangeably with obstructive uropathy, which refers to the damage to renal parenchyma resulting from urinary tract obstruction (UTO).
- More common in children than adults due to congenital anomalies.
- Hydronephrosis is more common in women for adults <60 years old and in men for adults >60 years old.
Etiology and Pathophysiology
- Hydronephrosis develops with increased pressure in the urinary collecting system, most commonly from some form of obstruction.
- Nonobstructive hydronephrosis can occur in the setting of very high urinary output such as with diabetes insipidus or as a physiologic change in pregnancy.
- Hydronephrosis may be acute/chronic, partial/complete, and uni-/bilateral.
- Obstruction may occur at an level of the GU system:
- Kidney: nephrolithiasis, transitional cell carcinoma, sloughed renal papillae, congenital ureteropelvic junction (UPJ) obstruction, blood clot, fungal ball
- Ureter: nephrolithiasis, transitional cell carcinomas, strictures, sloughed renal papillae, retroperitoneal fibrosis, extrinsic compression
- Bladder: neurogenic bladder, extrinsic compression, posterior urethral valves
- Urethra: prostatic hypertrophy or cancer, strictures
- Hydronephrosis in a transplanted kidney is more common than in native kidneys, due to ureteral reflux, strictures, ureteral compression (from peritransplant lymphoceles, hematomas) and bladder dysfunction.
- Antenatal hydronephrosis is diagnosed in 1–5% of pregnancies, usually by US, as early as the 12th to 14th week of gestation.
- Children with antenatal hydronephrosis are at greater risk of postnatal pathology.
- Postnatal evaluation begins with US exam; further studies, such as voiding cystourethrogram (VCUG), based on the severity of postnatal hydronephrosis
- In neonates, it is the most common cause of abdominal mass.
- Common etiologies in children are VUR, congenital UPJ obstruction, neurogenic bladder, and posterior urethral valves.
- Pediatric diagnostic algorithm differs from adult due to different differential diagnosis necessitating age-appropriate testing.
- Physiologic hydronephrosis in pregnancy is more prominent on the right than left and can be seen in up to 80% of pregnant women.
- Dilatation is caused by hormonal effects, external compression from expanding uterus, and intrinsic changes in the ureteral wall.
- Despite high incidence, most cases are asymptomatic.
- If symptomatic and refractory to medical management, ureteric calculus should be considered and urinary infection must be excluded.
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