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Hydronephrosis

Hydronephrosis is dilatation of the renal pelvis and calyces caused by impaired drainage of urine. Persistent or severe obstruction can increase pressure within the kidney and lead to progressive renal damage

Also called

Dilatation of the renal collecting system

ICD-10

N13.30

Specialty

Urology

Onset

Acute & Chronic

Reviewed

August 2026
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Overview

-Hydronephrosis occurs when urine cannot drain normally from the kidney, causing dilatation of the collecting system.

 

It may be:

  • Unilateral or bilateral
  • Acute or chronic
  • Mild, moderate, or severe
  • Obstructive or non-obstructive

 

–Common causes include urinary stones, UreteroPelvic Junction obstruction, prostatic enlargement, urethral obstruction, pregnancy, tumors, and congenital abnormalities.

Etiology & Risk Factors

-Etiology:

Hydronephrosis usually results from urinary tract obstruction or impaired urine drainage.

Important causes include:

  • Nephrolithiasis causing ureteric obstruction
  • Ureteropelvic junction obstruction
  • Ureteric stricture
  • Benign Prostatic Hyperplasia (BPH)
  • Urethral obstruction, including Posterior Urethral Valves (PUV)
  • Pelvic or urinary tract tumors
  • Pregnancy-related ureteric compression
  • Neurogenic bladder
  • Vesicoureteral Reflux (VUR)

 

-Risk Factors

  • History of urinary stones
  • Congenital urinary tract abnormalities
  • Benign Prostatic Hyperplasia (BPH)
  • Pelvic malignancy or surgery
  • Pregnancy

Pathophysiology

Impaired urinary drainage → urine accumulates proximal to the obstruction → increased pressure in the renal pelvis and calyces → hydronephrosis → compression of renal tissue and reduced renal blood flow → tubular and nephron damage → reduced kidney function → Acute Kidney Injury (AKI) or Chronic Kidney Disease CKD if severe or prolonged

Clinical Presentation

–Symptoms

  • Hydronephrosis may be asymptomatic, especially when chronic.

    Possible symptoms include:

    • Flank pain
    • Renal colic
    • Abdominal discomfort
    • Nausea and vomiting
    • Difficulty passing urine
    • Reduced urine output
    • Urinary frequency
    • Fever when infection is present
    • Hematuria

 

-Signs:

  • Costovertebral angle tenderness
  • Flank tenderness
  • Palpable kidney in severe cases
  • Distended bladder when lower urinary tract obstruction is present
  • Fever and systemic illness when associated infection is present
Hydronephrosis Overview
Hydronephrosis Overview

History Taking

-Ask about:

  • Flank or abdominal pain
  • Sudden or gradual onset of symptoms
  • Previous urinary stones
  • Hematuria
  • Fever or chills
  • Dysuria
  • Urinary frequency or urgency
  • Difficulty voiding
  • Poor urinary stream
  • Reduced urine output or anuria
  • History of Benign Prostatic Hyperplasia (BPH)

Physical Examination

-General Examination

  • Temperature
  • Blood pressure
  • Hydration status
  • Signs of sepsis
  • Signs of Acute Kidney Injury (AKI) or Chronic Kidney Disease CKD when present

 

-System-Specific Examination:

  • Costovertebral angle tenderness
  • Flank or abdominal tenderness
  • Palpable abdominal mass in severe hydronephrosis
  • Palpable distended bladder in lower urinary tract obstruction

Investigations

-Biochemistry / Specific Tests

  • Serum creatinine and estimated kidney function

  • Serum electrolytes when significant obstruction or kidney impairment is suspected

  • Urinalysis for hematuria, pyuria, and protein

  • Urine culture when urinary tract infection is suspected

 

-Imaging

Renal and Bladder Ultrasound

The usual first-line imaging investigation for detecting Hydronephrosis.

It can assess:

  • Degree of collecting-system dilatation

  • Kidney size

  • Bladder distension

  • Post-void residual urine

  • Some structural abnormalities

 

-Non-Contrast CT

Useful when urinary stones are suspected.

 

-CT Urography or MR Urography

May be used to identify:

  • Level of obstruction

  • Ureteric strictures

  • Tumors

  • Complex urinary tract abnormalities

 

-Special / Confirmatory Tests

Further tests depend on the suspected cause and may include:

  • Diuretic renography to assess functional obstruction

  • Voiding Cystourethrogram (VCUG) when Vesicoureteral Reflux (VUR) or lower urinary tract obstruction is suspected

  • Cystoscopy for selected lower urinary tract causes

Diagnosis

-Diagnosis is based on:

Imaging demonstrating dilatation of the renal pelvis and calyces + identification of the underlying cause of impaired urinary drainage.

Renal function should be assessed in significant, bilateral, prolonged, or symptomatic Hydronephrosis

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Management

1. First-Line / Emergency Management

Urgent treatment is required when Hydronephrosis is associated with infection, sepsis, anuria, severe Acute Kidney Injury (AKI), or obstruction of a solitary functioning kidney.

Emergency management may include:

  • Intravenous fluids when appropriate

  • Analgesia

  • Antibiotics for infection

  • Urgent urinary tract decompression

 

2. Definitive Treatment

Definitive treatment depends on the underlying cause.

Examples include:

  • Stone treatment or removal

  • Correction of ureteropelvic junction obstruction

  • Treatment of ureteric strictures

  • Management of Benign Prostatic Hyperplasia (BPH)

  • Treatment of tumors causing obstruction

  • Correction of congenital abnormalities

 

3. Medical Treatment

Depending on the cause:

  • Analgesics

  • Antibiotics for confirmed or suspected infection

  • Medical expulsive therapy in selected ureteric stone cases

  • Medication for Benign Prostatic Hyperplasia (BPH) when appropriate

 

4. Surgical / Procedural Treatment

Urgent or elective procedures may include:

  • Ureteric stent placement

  • Percutaneous nephrostomy

  • Ureteroscopy

  • Pyeloplasty

  • Stone removal procedures

  • Transurethral or other treatment for bladder outlet obstruction

 

5. Supportive Management

  • Monitor urine output

  • Monitor serum creatinine and electrolytes

  • Treat the underlying cause

  • Follow-up imaging

Complications

  • Urinary tract infection
  • Pyelonephritis
  • Urosepsis
  • Renal atrophy
  • Acute Kidney Injury (AKI)
  • Chronic Kidney Disease CKD
  • Hypertension
  • Permanent loss of renal function

Prognosis

The prognosis depends mainly on the cause, severity, duration of obstruction, presence of infection, and whether one or both kidneys are affected. Acute obstruction relieved promptly may result in substantial recovery of kidney function. Prolonged severe obstruction can cause irreversible renal damage and progressive Chronic Kidney Disease CKD

Key Points / Clinical Pearls

  • Hydronephrosis is dilatation of the renal pelvis and calyces due to impaired urine drainage.
  • It is an anatomical finding rather than a disease by itself.
  • Urinary obstruction is a common cause.
  • Nephrolithiasis is an important cause of acute unilateral Hydronephrosis.
  • Bilateral Hydronephrosis may indicate lower urinary tract obstruction.
  • Renal and bladder ultrasound is the usual first-line investigation.
  • CT is particularly useful when urinary stones or another obstructing lesion are suspected.
  • Kidney function should be assessed in significant or bilateral disease.
  • Hydronephrosis may be asymptomatic when chronic.
  • Flank pain, hematuria, and nausea may occur.
  • Fever with an obstructed kidney suggests infection and requires urgent treatment.
  • An infected obstructed kidney is a urological emergency.
  • Urgent decompression may be performed using a ureteric stent or percutaneous nephrostomy.