Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis is considered to be physiologic in pregnant women. Clinical presentation depends on the acuity and extent of the obstruction. Patients can present with flank pain, dysuria, urgency, fever, a palpable abdominal mass, fever, and hypertension. Diagnosis includes imaging with ultrasonography, CT, or intravenous pyelography. Management is guided by the cause and degree of obstruction. Treatment includes pain control, fluid replacement, and relief of the obstruction, which may require surgery, depending on the cause.

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Hydronephrosis is defined as the dilation of the renal pelvis and calyces due to obstruction of urine outflow.


  • Incidence: about 3.1%
  • Hydronephrosis resolves spontaneously in 50% of cases.
  • Children:
    • Most often a transient and physiologic state
    • Most cases resolve spontaneously by 2 years of age.
  • Adults:
    • Men = women before age 20
    • Women > men between 20 and 60 years of age:
      • Due to pregnancy and gynecologic malignancy
      • Hydronephrosis is seen in 80% of pregnant women.
    • Men > women after 60 years of age, due to prostate disease


  • Children:
    • Transient/physiologic
    • Ureteropelvic junction obstruction:
      • Intrinsic stenosis of the proximal ureter
      • Extrinsic compression by an aberrant or accessory renal artery
    • Multicystic dysplastic kidney
    • Vesicoureteral reflux
    • Megaureter
    • Ureterocele
    • Posterior urethral valves
  • Adults:
    • Kidney:
      • Nephrolithiasis (most common cause in young adults)
      • Renal cysts
      • Cancer
    • Urinary system:
      • Ureteral stricture
      • Iatrogenic injury to ureters
      • Neurogenic bladder
      • Cystocele
      • Urethral stricture
    • Pelvis:
      • Ureteropelvic obstruction
      • Malignancy of the renal pelvis, ureter, bladder, or prostate
      • Benign prostatic hyperplasia
    • Extrinsic causes:
      • Pregnancy
      • Peripelvic cysts
      • Retroperitoneal fibrosis
      • Gynecologic malignancies
      • Retroperitoneal masses


  • Obstruction of the outward flow leads to urine accumulation and increased pressure in the urinary tract.
  • The GFR persists initially, contributing to increased pressure within the urinary tract.
  • High pressure is transmitted upward, leading to dilation of the collecting tubules and calyces.
  • Increased hydrostatic pressure inside the collecting system → compression of the renal and especially inner medullary vasculature, which causes:
    • Impaired concentrating ability
    • Ischemic tubular atrophy
    • Interstitial fibrosis
  • Recovery of renal function depends on the duration and extent of the obstruction.

Clinical Presentation

Clinical manifestations vary depending on the acuity of symptom onset, the degree, and the site of the obstruction.

  • Asymptomatic:
    • Slowly developing or partial obstruction
      • Tumor
      • Congenital ureteropelvic junction obstruction
    • Pregnancy
  • Pain:
    • Caused by acute complete or incomplete obstruction
    • Determined by site of obstruction
    • Upper urinary tract obstruction causes flank pain.
    • Lower urinary tract obstruction results in suprapubic pain with radiation to the labia or testicle.
  • Changes in urine volume:
    • Anuria is seen with bilateral complete hydronephrosis.
    • Polyuria:
      • Due to impaired concentrating ability
      • Seen with partial bilateral obstruction
  • Hypertension:
    • Most common in acute unilateral hydronephrosis
    • Occurs through activation of the renin-angiotensin system
  • Decreased GFR is seen in partial or complete bilateral hydronephrosis.
  • Hematuria
  • Fever: if urinary stasis causes infection
  • Urinary retention
  • Palpable bladder



  • Fever
  • Hematuria
  • Symptoms of lower urinary tract obstruction:
    • Hesitancy
    • Dribbling
    • Prolonged micturition
    • Weak stream
  • Pain:
    • Location
    • Quality 
    • Duration
    • Radiation
  • Symptoms of urinary tract infection:
    • Dysuria
    • Urgency
    • Incontinence
  • Nausea and vomiting

Physical exam findings

  • Costovertebral angle tenderness
  • Abdominal examination:
    • Palpable kidney or bladder
    • Tenderness
  • Digital rectal examination:
    • Prostatic enlargement
    • Prostatic nodules
    • Sphincter tone

Diagnostic testing

Laboratory studies:

  • Urinalysis:
    • Pyuria suggests the presence of inflammation.
    • Leukocyte esterase or nitrites indicate infection.
    • Hematuria may indicate the presence of stones, malignancy, or infection.
  • CBC: shows leukocytosis
  • Basic metabolic panel:
    • ↑ BUN and creatinine are seen in bilateral hydronephrosis and indicate renal failure.
    • Hyperkalemia and acidosis indicate severe renal insufficiency.


  • Imaging in adults:
    • Ultrasonography:
      • Preferred over CT for pregnant women
      • Not as sensitive as CT in detecting ureteral stones
    • CT: best imaging method to diagnose stones
    • IV pyelography:
      • Has low false positive rate compared to ultrasonography
      • Differentiates renal cysts from hydronephrosis
      • Used for follow-up of stones or assessment of anatomy after stone removal
    • Diuretic renography:
      • Performed in patients with hydronephrosis and no signs of obstruction
      • A diuretic is administered before renal scanning → increased urine flow → dilation of the collecting system and decreased washout of the contrast material
      • May worsen the pain
      • Pain and positive diuretic renogram suggest surgical correction
  • Imaging in children:
    • Ultrasonography: can also be done prenatally
    • Voiding cystourethrography: best imaging study to diagnose suspected vesicoureteral reflux
    • Diuretic renography
    • Magnetic resonance urography:
      • Better defines the anatomy
      • Used for surgery planning
    • Grading of antenatal hydronephrosis has been developed for prenatal and postnatal ureteropelvic-junction–type hydronephrosis.
Table: The Onen Grading System for hydronephrosis
IRenal pelvic dilation
IIGrade I + calyceal dilation
IIIGrade II + thinning of the medulla
IVGrade III + cortical thinning + no corticomedullary differentiation
Anterograde pyelography demonstrates Grade III left-sided hydronephrosis

Anterograde pyelography demonstrates grade III left-sided hydronephrosis with obstruction at the ureterovesical junction.

Image: “Antegrade pyelogram of grade III hydronephrosis with obstruction at the ureterovesical junction” by Erkan Efe, Murat Bakacak, Salih Serin, Eyüp Kolus, Önder Ercan, and Sefa Resim. License: CC BY 4.0


Management depends on the cause of obstruction, the degree of metabolic abnormality, and the presence of infection.

General recommendations

  • Analgesia:
    • NSAIDs
    • Acetaminophen
    • Oxycodone
    • Hydrocodone
  • Fluid replacement
  • Antibiotics if infection present:
    • Trimethoprim–sulfamethoxazole
    • Nitrofurantoin
    • Cephalosporins
    • Fluoroquinolone
  • Correction of metabolic abnormalities
  • Management of the underlying cause:
    • Nephrolithiasis:
      • Alpha and calcium channel blockers
      • Extracorporeal shockwave lithotripsy
      • Percutaneous nephrolithotomy
      • Laparoscopic/open surgery
    • Benign prostatic hyperplasia:
      • α1-receptor blockers (e.g., tamsulosin)
      • 5α-reductase inhibitors (e.g., finasteride)
    • Retroperitoneal fibrosis: corticosteroids
    • Ureteropelvic junction obstruction: pyeloplasty

Relief of obstruction

The goal is to decrease the pressure in the collecting system.

  • Indications:
    • Complete obstruction
    • Presence of infection
  • Lower urinary tract obstruction:
    • Urethral catheterization
    • Suprapubic catheterization
  • Upper urinary tract obstruction:
    • Placement of retrograde ureteric stents
    • Percutaneous nephrostomy: subsequent antegrade stenting can be done.


  • Chronic hydronephrosis causes ischemic injury, resulting in cortical and medullary atrophy, and permanent loss of renal function.
  • Hydronephrosis is reversible if the obstruction is promptly relieved.

Differential Diagnosis

  • Peripelvic cyst: cyst arising from renal hilus. A peripelvic cyst is contiguous to the renal pelvis and calyces; its exact etiology is not known. These cysts are thought to be congenital or to arise from lymphatic obstruction. Peripelvic cysts are asymptomatic, but they can distort the renal pelvis on the imaging. Diagnosis is with imaging, usually contrast-enhanced CT. Management includes percutaneous drainage or marsupialization.
  • Pyelonephritis: bacterial infection resulting in kidney inflammation. Patients may present with fever, flank pain, nausea, vomiting, and costovertebral angle tenderness. Diagnosis is based on history, physical examination findings, urinalysis, and urine cultures. Other diagnostic workup includes CBC, imaging, and blood cultures. Pyelonephritis can be managed in the outpatient or inpatient setting depending on the presence of risk factors and the severity of the disease. Management includes the administration of analgesics, antibiotics, and antipyretics.
  • Congenital megacalyces: rare, usually unilateral, condition caused by the underdevelopment of medullary pyramids resulting in the dilation of the calyces. Patients with congenital megacalyces are asymptomatic, but they can present with a urinary tract infection due to stasis. Diagnosis is based on imaging with ultrasonography, IV pyelography, or CT scan with contrast. Stones and infections are treated appropriately. Surgery is not required. 


  1. Ilgi, M., et al. (2020). Rare causes of hydronephrosis in adults and diagnosis algorithm: analysis of 100 cases during 15 years. Cureus 12(5):e8226. https://doi.org/10.7759/cureus.8226
  2. Lusaya, D.G. (2020). Hydronephrosis and hydroureter. Medscape. Retrieved June 9, 2021, from https://emedicine.medscape.com/article/436259-overview
  3. Fisher, J.S. (2020). Urinary tract obstruction. Medscape. Retrieved June 9, 2021, from https://emedicine.medscape.com/article/438890-overview
  4. Zeidel, M.L., O’Neill, W.C. (2019). Clinical manifestations and diagnosis of urinary tract obstruction and hydronephrosis. UpToDate. Retrieved June 29, 2021, from https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-urinary-tract-obstruction-and-hydronephrosis

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