Hydronephrosis and obstructive uropathy !

Hydronephrosis is swelling of the kidney's collecting system when urine cannot drain, usually from a blockage such as a stone or an enlarged prostate.

Updated 2026-11-01

Structures involved

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In the clinical exam

Kidney palpation: bimanual palpation and ballottement

Why it happens

What it is

Hydronephrosis is dilation of the renal pelvis and calyces; when the ureter is also dilated it is called hydroureteronephrosis. Obstructive uropathy is the blockage of urine flow anywhere from the kidney to the urethra, and obstructive nephropathy is the kidney damage it causes. Obstruction can be one-sided or both-sided, acute or chronic, partial or complete.

Who gets it

Found at all ages. In infants it is often detected on prenatal ultrasound (pelvi-ureteric junction obstruction, vesicoureteral reflux, posterior urethral valves in boys). In young adults stones dominate; in older men, prostate enlargement; in women, pregnancy and pelvic tumours such as cervical cancer, which remains a frequent cancer in Colombia and Latin America and a classic cause of bilateral ureteric obstruction.

Causes

Kidney or ureteric stones
Benign prostatic hyperplasia, prostate cancer or urethral stricture (bladder outlet obstruction)
Pelvic tumours: cervical, bladder, colorectal or ovarian cancer; retroperitoneal fibrosis or lymph nodes
Congenital: pelvi-ureteric junction obstruction, posterior urethral valves, vesicoureteral reflux
Neurogenic bladder (spinal cord injury, diabetes, multiple sclerosis)
Pregnancy (physiological dilation, more on the right) and ureteric injury after pelvic surgery
Blood clots, sloughed papillae or ureteric strictures

Risk factors

Previous kidney stones
Male sex and older age (prostate disease)
Pelvic cancer, radiotherapy or surgery
Neurological disease affecting bladder emptying
Pregnancy
Single functioning kidney (any obstruction is critical)

Pathophysiology

Blocked outflow raises pressure in the ureter and pelvis, which is transmitted back to the tubules and lowers glomerular filtration. Early on, renal blood flow rises, then falls as vasoconstriction follows. Prolonged pressure causes tubular atrophy, interstitial inflammation and fibrosis, so function lost after weeks may not return. Stagnant urine also favours infection and stone formation. After relief of a bilateral obstruction, the damaged tubules may lose large amounts of water and salt (post-obstructive diuresis).

Classification

Unilateral versus bilateral (or obstruction of a single kidney)
Acute versus chronic; partial versus complete
Upper tract (kidney, ureter) versus lower tract (bladder outlet, urethra)
Ultrasound grading of dilation (mild, moderate, severe) and, in infants, the SFU or UTD systems

Symptoms and signs

Acute: colicky flank pain radiating to the groin, nausea and vomiting (stones)
Chronic: often silent, or a dull flank ache
Reduced or absent urine output (bilateral or bladder outlet obstruction)
Weak stream, hesitancy, frequency and incomplete emptying (prostate)
Palpable bladder or flank mass
Haematuria, fever and dysuria when infection is present
Hypertension or signs of kidney failure in long-standing obstruction

Diagnosis

Clinical: Pain pattern, urinary symptoms, palpable bladder, digital rectal examination in men and pelvic examination in women; review of past stones, cancers, surgery and neurological disease.
Tests: Creatinine, urea and electrolytes (potassium); complete blood count; urinalysis and urine culture; post-void residual volume by bladder scan; PSA where relevant.
Imaging: Kidney and bladder ultrasound is the first test (no radiation, safe in pregnancy and kidney failure). Non-contrast CT identifies stones and the level of blockage; contrast CT or MRI urography for tumours; diuretic renography (MAG3) measures split function and true obstruction; voiding cystourethrogram in children.

Differential diagnosis

Physiological dilation in pregnancy
Vesicoureteral reflux without obstruction
Extrarenal pelvis (a normal variant)
Parapelvic kidney cysts
Polycystic kidney disease

Goal of treatment

Relieve the obstruction quickly, treat infection, protect kidney function and correct the cause so it does not return.

Treatment

Acute: Infected obstruction is an emergency: intravenous antibiotics plus urgent drainage. Pain relief with NSAIDs or opioids and antiemetics for colic.
Procedure: Drainage: urinary catheter for bladder outlet obstruction; ureteric stent or percutaneous nephrostomy for upper tract obstruction.
Surgical: Definitive treatment of the cause: ureteroscopy, lithotripsy or percutaneous removal of stones; prostate surgery; pyeloplasty for pelvi-ureteric junction obstruction; oncological treatment of pelvic tumours.
Medical: Medical expulsive therapy with alpha-blockers for small distal ureteric stones; alpha-blockers and 5-alpha-reductase inhibitors for prostate enlargement.
Follow-up: Nursing care: urine output and fluid balance, care of catheters and nephrostomy tubes, signs of infection, and electrolytes during post-obstructive diuresis.

Complications

Acute kidney injury and chronic kidney disease
Pyelonephritis, pyonephrosis and urosepsis
Post-obstructive diuresis with dehydration and electrolyte loss
Hyperkalaemia and metabolic acidosis
Hypertension
Stone formation

Prognosis

Function usually recovers if obstruction is relieved within days to a few weeks. Long-standing complete obstruction can cause permanent loss of the affected kidney. Bilateral obstruction from advanced pelvic cancer carries a poor outlook driven by the cancer.

Prevention

Prevention of stone recurrence (fluids, diet, treating metabolic causes)
Early evaluation of urinary symptoms in men
Follow-up of prenatal hydronephrosis in infants
Cervical cancer screening and HPV vaccination

Test yourself

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What is the first-line imaging test for suspected hydronephrosis?

Kidney and bladder ultrasound.

Why is an obstructed, infected kidney a urological emergency?

It can rapidly cause urosepsis; it needs intravenous antibiotics plus urgent drainage by stent or nephrostomy.

What is the most common cause of bilateral hydronephrosis in an older man?

Bladder outlet obstruction from benign prostatic hyperplasia.

What should nurses watch for after relieving a bilateral obstruction?

Post-obstructive diuresis: very high urine output with dehydration and loss of sodium and potassium.

Which congenital cause of hydronephrosis affects only boys?

Posterior urethral valves.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Obstructive uropathy: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); Bilateral hydronephrosis: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2025).

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Representative model, for educational purposes only.

Renal pelvis highlighted on the Durgical 3D model