What causes Hydrouretero nephrosis?

Causes of Hydroureteronephrosis

Hydroureteronephrosis results from obstruction at any level of the urinary tract, with the specific etiology varying by age: urolithiasis predominates in adults, while ureteropelvic junction (UPJ) obstruction is the leading cause in pediatric and antenatal cases. 1

Primary Etiologic Categories by Mechanism

Obstructive Causes (Most Common)

Intrinsic Obstruction:

• Urolithiasis is the most common cause in adults, creating mechanical blockage of the ureter 1
• Ureteropelvic junction (UPJ) obstruction is the predominant cause in antenatal and pediatric hydronephrosis 1
• Urothelial malignancies (transitional cell carcinoma of ureter or renal pelvis) can cause intrinsic obstruction 1
• Ureteral strictures from prior instrumentation, infection, or inflammation 1
• Posterior urethral valves in males require urgent intervention and are a critical pediatric cause 1
• Primary megaureter represents functional obstruction at the ureterovesical junction 1

Extrinsic Compression:

• Pelvic or retroperitoneal tumors compressing the ureters (cervical, ovarian, colorectal, prostate cancers) 1
• Retroperitoneal fibrosis can cause functional obstruction while allowing some drainage 2
• Pregnancy-related compression becomes pathologic when anteroposterior diameter exceeds 27.5mm in third trimester with symptoms 3

Bladder Outlet Obstruction:

• Prostatic hyperplasia (benign or malignant) is increasingly important with age 1
• Neurogenic bladder from spinal cord injury or neurologic disease 1

Non-Obstructive Causes

Vesicoureteral Reflux:

• A major consideration in pediatric populations causing dilation without true obstruction 1
• Approximately 80% of mild to moderate pediatric cases resolve without intervention 3

Congenital Nephrotic Syndromes:

• Cause hydroureteronephrosis due to hypoproteinemia in fetal/neonatal period 4
• Surviving infants may have massive proteinuria at birth and develop renal failure in childhood 4

Ruptured Collecting System:

• Ruptured bladder or renal collecting system may cause urinary ascites and mimic hydroureteronephrosis 4

Age-Specific Diagnostic Approach

Antenatal/Pediatric Population:

• UPJ obstruction accounts for the majority of cases 1
• Most antenatal hydronephrosis is transient with little long-term significance 1
• Isolated mild hydronephrosis in a fetus carries minimal aneuploidy risk 3
• Vesicoureteral reflux must be excluded as a major differential 1
• 24% of pediatric cases resolve completely without intervention 3

Adult Population:

• Urolithiasis is the predominant acute cause 1
• Chronic non-stone-related hydronephrosis from bladder dysfunction is often detected incidentally 1
• Malignant obstruction becomes increasingly important with advancing age 1
• Hematuria and weight loss are poor predictive factors suggesting malignancy (malignancy rate 100% with weight loss vs 17.6% without) 5

Critical Clinical Pitfalls to Avoid

Emergent Situations Requiring Immediate Recognition:

• Bilateral hydroureteronephrosis is a medical emergency requiring urgent decompression, as serum creatinine will be elevated 1
• Pyonephrosis (infected obstructed system) requires urgent decompression before definitive treatment 1
• Posterior urethral valves in males demand urgent intervention to prevent irreversible renal damage 1

Diagnostic Errors:

• A distended bladder must be decompressed before re-evaluation, as it can cause false-positive hydronephrosis 3
• Chronic hydroureteronephrosis can be asymptomatic until significant renal damage occurs 1
• Progressive dilation leads to acute kidney injury and permanent nephron loss if not corrected 1, 6
• Intermittent or positional obstruction may not be present during imaging studies, leading to false negative results 2

Malignancy Considerations:

• Despite further investigations, etiology cannot be determined in approximately 5% of cases, warranting continued surveillance 5
• The frequency of malignancy in patients with hematuria is two times higher than in those without (33% vs 17.6%) 5
• Giant hydronephrosis with concurrent malignancy is easily misdiagnosed and requires histopathologic examination 7