What are the causes of hydronephrosis in adults and pediatric patients?

Causes of Hydronephrosis

Hydronephrosis results from urinary obstruction or reflux, with urolithiasis being the most common cause in both adults and children (54.1% of cases), followed by vesicoureteral reflux, structural abnormalities, and malignant obstruction. 1, 2

Primary Etiologic Categories

Hydronephrosis can be classified by mechanism (obstructive vs. non-obstructive), laterality (unilateral vs. bilateral), and level of obstruction (intrinsic vs. extrinsic). 1

Obstructive Causes

Stone Disease (Most Common)

• Urolithiasis accounts for 54.1% of all hydronephrosis cases 2
• Stones most commonly lodge at the vesicoureteric junction (25.3%), followed by renal pelvis (21.5%), pelviureteric junction/upper ureter (6.4%), and rarely middle ureter (0.9%) 2
• This is the leading cause even in pediatric populations 2

Structural/Anatomic Abnormalities

• Ureteropelvic junction (UPJ) obstruction—the most common cause in pediatric antenatal hydronephrosis 1, 3
• Strictures (post-surgical, post-radiation, ischemic injury) 1
• Posterior urethral valves in male infants 1
• Primary megaureter 1
• Congenital anomalies such as retrocaval ureter 4

Bladder and Lower Tract Dysfunction

• Bladder outlet obstruction from prostatic hyperplasia 1
• Neurogenic bladder or other bladder dysfunction 1
• Large post-void residual volumes (>350 mL in adults) 5

Malignant Obstruction

• Intrinsic urothelial malignancies 1
• Extrinsic compression from pelvic or retroperitoneal tumors 1

Inflammatory/Infectious

• Retroperitoneal fibrosis 1
• Upper urinary tract infection with pyonephrosis 1, 6
• Schistosomiasis 1

Mechanical Compression

• Enlarged uterus during pregnancy (70-90% of pregnant patients develop asymptomatic hydronephrosis, typically right-sided) 1, 5, 7
• Pelvic organ prolapse 1
• Endometriosis 1

Drug-Induced

• Cyclophosphamide 1
• Ketamine 1

Non-Obstructive Causes

Vesicoureteral Reflux (VUR)

• Accounts for 7.3% of hydronephrosis cases 2
• More common in pediatric populations 1
• Resolution rates: 80% for grades I-II, 30-50% for grades III-V within 4-5 years 5

Age-Specific Considerations

Pediatric Population

• UPJ obstruction is the predominant cause in antenatal hydronephrosis 1, 3
• Vesicoureteral reflux is a major consideration 1
• Posterior urethral valves in males require urgent intervention 1
• Most antenatal hydronephrosis is transient with little long-term significance 1

Adult Population

• Urolithiasis predominates (54.1% of cases) 2
• Chronic non-stone-related hydronephrosis from bladder dysfunction is often detected incidentally 1, 7
• Malignant obstruction becomes increasingly important with age 1
• Upper urinary tract deterioration can be silent and detected incidentally 1

Pregnancy-Related

• Asymptomatic hydronephrosis occurs in 70-90% of pregnant patients due to mechanical compression and progesterone-induced smooth muscle relaxation 1, 5, 7
• Only 0.2-4.7% develop symptomatic hydronephrosis, with higher prevalence in advancing trimesters and multiparous patients 1, 5, 7
• Symptomatic cases may lead to preterm labor or maternal/fetal death if untreated 1, 7

Critical Clinical Pitfalls

Bilateral vs. Unilateral Disease

• Bilateral hydronephrosis is a medical emergency requiring urgent decompression, as serum creatinine will be elevated (unlike unilateral cases where contralateral compensation occurs) 1, 7, 8

Delayed Recognition

• Chronic hydronephrosis can be asymptomatic until significant renal damage occurs 1, 7
• Progressive dilation leads to acute kidney injury and permanent nephron loss if not corrected 1, 7, 9

Infection Superimposed on Obstruction

• Pyonephrosis requires urgent decompression (percutaneous nephrostomy or retrograde stenting) before definitive treatment 8, 6

Pregnancy Mismanagement

• Do not assume all pregnancy-related hydronephrosis is physiologic—symptomatic cases require intervention 1, 7