OVERVIEW

What is hydronephrosis?

The urinary system consists of the kidneys, ureters, bladder, and urethra. The renal pelvis, calyces, ureters, bladder, and urethra form what we commonly refer to as the urinary tract, which is the pathway for urine excretion.

When the urinary tract becomes obstructed due to various reasons, poor drainage can occur, leading to dilation and fluid accumulation in the renal pelvis and calyces. Common causes of hydronephrosis include stones, tumors, infections, and congenital malformations of the urinary system. It can develop after acute obstruction or progress chronically. Acute obstruction often results in milder hydronephrosis but can cause significant damage to kidney function in a short period.

Hydronephrosis can affect one kidney or both. In chronic cases, early symptoms are often absent, but late-stage symptoms may include back pain. If both kidneys are affected, reduced urine output may also occur.

Treatment for hydronephrosis focuses on draining urine, preserving kidney function, and addressing the underlying cause, often requiring surgical intervention.

Is hydronephrosis common?

Clinically, hydronephrosis caused by various factors is relatively common overall.

SYMPTOMS

What are the common manifestations of hydronephrosis?

The clinical manifestations of hydronephrosis vary depending on the cause, location, duration, and severity of the obstruction.

• If the obstruction occurs in the upper urinary tract (the part above where the ureter enters the bladder), it directly affects the kidneys, and hydronephrosis or related symptoms often appear earlier. If the obstruction is below the bladder outlet (urethra), due to the buffering effect of the bladder, it may take longer for the kidneys to show signs, such as hydronephrosis or impaired renal function. In such cases, both kidneys and ureters (upper urinary tract) are usually affected simultaneously.
• If the urinary tract obstruction occurs acutely, symptoms are often more pronounced, such as renal colic, nausea, vomiting, hematuria, and tenderness in the kidney area. However, if the onset is slow, or if only one kidney is affected, there may be no obvious clinical manifestations in the early stages of hydronephrosis. As the disease progresses, back or abdominal pain may occur, but these symptoms are nonspecific and often overlooked.
• If the obstruction involves both upper urinary tracts or the single functioning kidney, reduced urine output or even complete anuria may occur. Without timely drainage, this can lead to renal impairment or kidney failure.
• Urinary tract obstruction can easily trigger infections, leading to symptoms such as fever, nausea, frequent urination, urgency, and dysuria. However, in cases of complete obstruction, if the infection occurs above the obstruction, urine in the bladder may come from the unaffected kidney, resulting in no urinary abnormalities or even normal urine test results.
• Hydronephrosis can be caused by conditions such as stones, tumors, or tuberculosis, often presenting with symptoms of these underlying diseases.

What are the manifestations of unilateral and bilateral hydronephrosis?

• If only one kidney is affected by hydronephrosis, the other kidney can compensate for the impaired function, so overall renal function (measured by blood tests such as creatinine and urea nitrogen) may remain unchanged. However, as the disease progresses, symptoms like back pain on the affected side may appear.
• Bilateral hydronephrosis or hydronephrosis in a solitary kidney can lead to overall renal impairment, resulting in reduced urine output or even anuria, eventually progressing to kidney failure.

How does hydronephrosis develop?

The human urinary system consists of four main parts: the kidneys, ureters, bladder, and urethra. The renal pelvis, ureters, bladder, and urethra form the urinary tract, which is the pathway for urine excretion.

The kidneys' primary function is to filter metabolic waste and excess water from the body, forming urine that is excreted through the urinary tract. Obstruction due to various causes prevents urine from flowing smoothly from the kidneys to the bladder or allows urine in the bladder to reflux into the kidneys. This leads to urine accumulation in the renal pelvis and calyces (the internal structures of the kidneys), causing dilation of the renal pelvis and calyces, atrophy of the renal parenchyma, and ultimately hydronephrosis.

Additionally, urethral obstruction, if prolonged, can also prevent urine from draining from the kidneys into the bladder, leading to hydronephrosis.

What diseases can hydronephrosis cause?

Complications of hydronephrosis include:

• Increased susceptibility to infections, presenting as fever, chills, back pain, frequent urination, urgency, dysuria, hematuria, or cloudy urine. However, in cases of complete unilateral upper urinary tract obstruction, infected urine may not enter the bladder, and urine from the unaffected kidney may appear normal, showing no urinary abnormalities or even normal test results.
• Renal impairment: Symptoms may include fatigue, loss of appetite, edema, reduced urine output, and darker urine. As the condition worsens, kidney failure may occur, leading to oliguria or anuria. Without proper excretion of waste, immediate hemodialysis is required to prevent life-threatening complications.

CAUSES

What Causes Hydronephrosis?

Any condition that causes urinary tract obstruction can lead to hydronephrosis. Common causes include congenital diseases, infectious diseases, acquired obstructive diseases, and others.

• Congenital diseases: Primarily involve congenital anatomical abnormalities or functional disorders of the urinary system, such as segmental absence of peristalsis in the ureteropelvic junction, ureteral strictures, ectopic vascular compression of the ureter, or vesicoureteral reflux.
• Infectious diseases: Infections can cause strictures in the ureter, ureteral orifice, or urethra, particularly certain infections like tuberculosis.
• Acquired diseases: Conditions such as urinary stones, tumors, benign prostatic hyperplasia, trauma, as well as extraurinary factors like abdominal or pelvic tumors, and even certain physiological phenomena, can lead to urinary tract obstruction.

Who Is Prone to Hydronephrosis?

Hydronephrosis can occur in anyone, with no specific high-risk group.

Is Hydronephrosis Contagious or Hereditary?

There is currently no evidence that hydronephrosis itself is contagious or hereditary. However, the underlying conditions causing hydronephrosis may be hereditary or potentially infectious.

DIAGNOSIS

What tests are needed to diagnose hydronephrosis?

• Urine and blood tests: These can assess kidney function and check for concurrent infections, helping identify systemic diseases that may cause hydronephrosis.
• Urinary tract ultrasound: A key diagnostic tool for hydronephrosis. This simple, non-invasive, and cost-effective test can reveal kidney morphology and basic urinary tract conditions, such as stones or tumors, identifying most causes of hydronephrosis.
• CT and MRI: These can evaluate the kidneys and urinary tract while also detecting abnormalities in adjacent organs (e.g., prostate, cervix, colon) to determine the underlying cause of hydronephrosis.
• Intravenous pyelography (IVP): This may be performed when necessary to directly observe kidney and urinary tract structures, roughly assess kidney function based on contrast imaging, and guide treatment planning.
• Renal scintigraphy or dynamic renal imaging: These can separately evaluate the functional status of both kidneys.
• Retrograde pyelography: A catheter is inserted through the urethra or ureter to inject contrast dye for urinary tract visualization. This invasive procedure carries risks like infection.
• Endoscopy (e.g., cystoscopy, ureteroscopy): Helps identify obstruction causes and enables treatments like stone removal, stricture incision, or tumor resection.

Why are these tests necessary for hydronephrosis? What precautions should be taken?

• Urine/blood tests preliminarily assess kidney dysfunction, UTIs, hematuria, or proteinuria. Midstream urine samples should be collected to avoid contamination.
• Ultrasound screens for hydronephrosis. While routine urinary ultrasounds require a full bladder, suspected hydronephrosis cases should avoid bladder filling to prevent worsening.
• CT/MRI evaluates urinary and adjacent tissues to identify underlying causes. Patients with metal implants must inform doctors before MRI. Remove all ferromagnetic/electronic items during scans.
• IVP clearly shows urinary obstructions, aiding severity assessment and treatment planning. Iodine contrast is used; caution needed for those allergic to iodine, with kidney dysfunction, or hyperthyroidism.
• Retrograde pyelography risks infections. Avoid if patients show infection signs like fever or abnormal urine.

What diseases can hydronephrosis be confused with?

Hydronephrosis itself is detectable via imaging (ultrasound/CT) but may resemble renal cysts or abscesses. More crucially, the underlying cause requires accurate diagnosis and differentiation.

TREATMENT

Which department should I visit for hydronephrosis?

For hydronephrosis, you should visit the urology or nephrology department.

What are the current treatment options for hydronephrosis?

The general treatment principles for hydronephrosis are to ensure unobstructed urine drainage, protect kidney function, and address the underlying cause.

• Removing the cause: Conditions such as stones, tumors, or congenital abnormalities often require surgical intervention.
• Temporary drainage: For patients with identifiable causes who cannot undergo surgery immediately, options include percutaneous nephrostomy (direct drainage from the kidney to the outside) or ureteral stenting (internal drainage from the kidney to the bladder). These methods provide temporary relief until surgery is feasible, though some patients may need long-term drainage tubes.
• Medication: Depending on the cause or complications (e.g., infections), antibiotics or other drugs may be prescribed.

• Dialysis: Severe hydronephrosis may lead to kidney failure, necessitating dialysis to remove metabolic waste and excess fluids, which can be life-threatening if untreated.

Can hydronephrosis resolve on its own?

Mild hydronephrosis may improve if the underlying cause is addressed promptly. However, in some cases, while further damage can be halted, the existing condition may not fully reverse. Early treatment reduces the risk of kidney failure or life-threatening complications.

What are the common risks of surgery for hydronephrosis?

Risks include anesthesia-related complications, bleeding, infection, acute organ injury, and the possibility that hydronephrosis may persist post-surgery.

What is the prognosis after treatment for hydronephrosis?

• Patients with mild hydronephrosis and treatable causes often recover fully without significant complications.
• Prognosis varies by cause; for example, hydronephrosis due to malignant tumors may involve complications like chemotherapy side effects or metastasis.
• Advanced cases with irreversible kidney damage may progress to kidney failure, requiring lifelong dialysis and posing life-threatening risks.

Is follow-up necessary for hydronephrosis? How is it done?

Yes, follow-up is essential. The schedule depends on the underlying cause and should follow medical advice. Key assessments include kidney function tests and imaging to evaluate structural changes.

Can hydronephrosis be cured?

Some causes, like pregnancy or urinary stones, can be fully resolved, leading to a cure. However, irreversible causes or severe cases with kidney failure may require long-term management without a complete cure.

DIET & LIFESTYLE

What should patients with hydronephrosis pay attention to in their diet?

Patients with hydronephrosis have different dietary requirements depending on the underlying cause.

• Patients with urinary stones should drink plenty of water and avoid foods high in oxalates, such as chocolate and nuts.
• Patients with existing renal insufficiency should control salt and protein intake, opting for high-quality protein sources.
• Maintain a balanced diet and avoid spicy or irritating foods.
• Depending on the specific cause, there may be additional dietary restrictions. Follow medical advice or consult a nutrition professional for a tailored diet plan.

What should patients with hydronephrosis pay attention to in daily life?

• Engage in moderate exercise, combining aerobic and strength training, as long as physical condition allows. Avoid excessive intensity.
• Ensure sufficient daily sleep, avoid staying up late, and maintain a regular schedule.
• Learn to manage stress and emotional tension.
• Seek medical attention promptly if discomfort occurs. Follow up with regular check-ups as advised by the doctor.

Does hydronephrosis affect normal life, study, or work?

If treated promptly without complications, hydronephrosis generally does not interfere with daily activities. However, severe cases may lead to acute kidney failure, causing reduced or no urine output. If the underlying condition remains untreated, it may disrupt normal life, study, or work.

PREVENTION

Can Hydronephrosis Be Prevented? How to Prevent It?

Depending on the cause of hydronephrosis, some cases can be prevented to a certain extent. For example, patients with kidney stones can prevent stone formation by drinking more water and adjusting their diet. However, for most causes, such as tumors or congenital malformations, there are no definitive preventive methods.

How Can Hydronephrosis Patients Avoid Serious Complications?

Patients with hydronephrosis should regularly undergo follow-up examinations, including urinary system ultrasounds, kidney function tests, and urine tests. In daily life, if physical changes occur—such as back pain, fever, high blood pressure, or changes in urination—they should seek medical attention promptly to avoid complications.