Hydronephrosis and Pyonephrosis

 

Pyonephrosis (Infected Hydronephrosis)

Pyonephrosis is a serious condition that occurs when a hydronephrotic (dilated and obstructed) kidney becomes infected, leading to the accumulation of pus within the renal collecting system. It is essentially an abscess within an obstructed kidney and represents a urological emergency requiring prompt drainage and antibiotic therapy. The stagnant urine in hydronephrosis provides an ideal medium for bacterial growth. Symptoms of pyonephrosis are often more severe than uncomplicated hydronephrosis and include high fever, chills, severe flank pain, tenderness, and signs of systemic sepsis. The urine may be cloudy and foul-smelling.

 

Diagnosis of Hydronephrosis and Pyonephrosis

The diagnosis of hydronephrosis and its underlying cause, as well as the detection of pyonephrosis, involves several diagnostic modalities:

• Medical History and Physical Examination: Including assessment of symptoms, risk factors, and palpation for an enlarged kidney or bladder.
• Urinalysis: To check for infection (pyuria, bacteriuria, positive nitrites), hematuria, proteinuria, or crystals.
• Blood Tests: To assess kidney function (creatinine, BUN, eGFR), electrolytes, and signs of infection (white blood cell count, C-reactive protein).
• Kidney Ultrasound (Renal Ultrasound): This is often the initial imaging test. It can readily detect dilation of the renal pelvis and calyces (pyelocaliceal system) and assess the degree of renal parenchymal atrophy. It can also identify some causes of obstruction like large stones or tumors, and can show debris within the collecting system suggestive of pyonephrosis.
• Excretory Urography (Intravenous Pyelogram - IVP): (Less commonly used now with the advent of CT urography). This X-ray study involves injecting intravenous contrast material that is excreted by the kidneys. It can identify the expansion of the pelvicalyceal system, delineate the site of obstruction, and indirectly assess the function of the affected kidney (e.g., delayed excretion of contrast).
• Computed Tomography (CT) Scan: A CT urogram provides detailed images of the urinary tract and is excellent for identifying the cause and level of obstruction (stones, tumors, strictures, extrinsic compression), assessing kidney anatomy, and detecting complications like pyonephrosis (which may show as dense fluid/debris in the collecting system, perinephric stranding, or gas).
• Magnetic Resonance Imaging (MRI): MRI urography can be used as an alternative to CT, especially in patients who cannot receive iodinated contrast or require radiation avoidance (e.g., pregnant women, children).
• Radionuclide Renography (e.g., MAG3 or DTPA scan): A nuclear medicine scan that assesses differential renal function and can help determine the functional significance of an obstruction by evaluating drainage patterns after diuretic administration (diuretic renography).
• Voiding Cystourethrography (VCUG): Primarily used in children to diagnose vesicoureteral reflux or posterior urethral valves.
• Retrograde or Antegrade Pyelography: Invasive procedures where contrast is injected directly into the ureter/renal pelvis (retrograde, via cystoscopy) or percutaneously into the kidney (antegrade) to precisely define the anatomy of an obstruction. These are often done in conjunction with therapeutic interventions.

 

Treatment of Hydronephrosis and Pyonephrosis

General Principles

The primary goal of treating hydronephrosis is to relieve the obstruction to the normal outflow of urine from the kidney, thereby preserving or improving kidney function and alleviating symptoms. For pyonephrosis, urgent drainage of the infected collecting system and systemic antibiotic therapy are paramount.

 

Surgical Management

Surgical or procedural intervention is often required for hydronephrosis and is essential for pyonephrosis.

• Relief of Obstruction:
  • Ureteral Stent Placement: A thin tube (stent) can be placed endoscopically (via cystoscopy) through the bladder into the ureter to bypass the obstruction and allow urine to drain from the kidney to the bladder.
  • Percutaneous Nephrostomy: A tube is inserted directly into the kidney through the skin of the back under imaging guidance (ultrasound or fluoroscopy) to drain urine externally. This is often a temporizing measure to decompress an obstructed or infected kidney, especially in pyonephrosis or severe obstruction causing renal failure.
• Definitive Correction of the Cause: The earlier the definitive plastic surgery or other corrective procedure is performed, the greater the chances of preserving kidney function.
  • Pyeloplasty: Surgical repair of a ureteropelvic junction (UPJ) obstruction.
  • Ureteral Reimplantation or Ureteroureterostomy: For ureteral strictures or UVJ obstruction.
  • Stone Removal: Endoscopic procedures (ureteroscopy, percutaneous nephrolithotomy - PCNL), extracorporeal shock wave lithotripsy (ESWL).
  • Tumor Resection or Management.
  • Treatment of BPH (e.g., TURP, medications).
  • Correction of PUV in infants.
• Staged Procedures: In cases of severe hydronephrosis with significant renal impairment or infection (pyonephrosis), treatment may be staged. Initially, a nephrostomy tube is placed to drain the kidney and allow the patient's condition (and kidney function) to stabilize and infection to be controlled. Once the patient is stable and renal function has recovered to some extent, definitive plastic surgery of the ureter and pelvis (e.g., pyeloplasty) or other corrective procedure is performed.
• Nephrectomy (Kidney Removal): In advanced forms of hydronephrosis where the affected kidney has minimal or no remaining function and is a source of recurrent pain or infection (especially if pyonephrosis develops and cannot be controlled), removal of the kidney (nephrectomy) may be indicated to avoid further infectious complications, provided the contralateral kidney is functioning normally.

 

Differential Diagnosis of Flank pain and Kidney Swelling

When a patient presents with flank pain and/or evidence of kidney swelling (hydronephrosis), several conditions should be considered:

Condition	Key Differentiating Features
Hydronephrosis/Pyonephrosis	Flank pain (colicky or dull), +/- fever/chills (if pyonephrosis), nausea/vomiting. Imaging (ultrasound, CT) shows dilated renal collecting system; underlying obstruction identified. Pyuria/bacteriuria if infected.
Acute Pyelonephritis (without significant obstruction)	Flank pain, fever, chills, dysuria, urgency, frequency. Urinalysis shows pyuria, bacteriuria. Imaging may show renal inflammation but not necessarily significant hydronephrosis unless obstruction develops.
Renal Calculus (Kidney Stone) without significant obstruction	Severe colicky flank pain, hematuria, nausea/vomiting. Stone visible on CT or ultrasound. Hydronephrosis may be mild or absent if stone is non-obstructing or has passed.
Renal Cyst (Simple or Complex)	Often asymptomatic. Large cysts can cause dull flank pain or pressure. Ultrasound/CT shows cystic lesion. Hemorrhage into a cyst can cause acute pain.
Renal Tumor (e.g., Renal Cell Carcinoma)	Often asymptomatic initially. Classic triad (rare): flank pain, hematuria, palpable mass. Diagnosed by imaging (CT/MRI). Can cause hydronephrosis if obstructing collecting system.
Musculoskeletal pain (e.g., Muscle Strain, Rib Fracture)	pain often related to movement or specific posture, localized tenderness. No urinary symptoms or imaging signs of hydronephrosis.
Perinephric Abscess	Fever, flank pain, tenderness. Collection of pus around the kidney, often a complication of severe pyelonephritis. Diagnosed by CT/ultrasound.
Gastrointestinal Conditions (e.g., Appendicitis, Diverticulitis, Bowel Obstruction)	Abdominal pain (may radiate to flank), nausea, vomiting, changes in bowel habits. Specific GI signs and imaging findings.

 

Potential Complications

Untreated or inadequately managed hydronephrosis and pyonephrosis can lead to significant complications:

• Progressive Loss of Kidney Function: Leading to chronic kidney disease or end-stage renal disease.
• Pyonephrosis and Sepsis: Infection of a hydronephrotic kidney can lead to severe systemic infection (urosepsis), which is life-threatening.
• Kidney Stone Formation: Urinary stasis predisposes to stone development.
• Recurrent Urinary Tract Infections.
• Hypertension: Can be caused by impaired renal blood flow and activation of the renin-angiotensin system.
• Rupture of the Renal Pelvis or Fornices: Rare, but can occur with acute, high-pressure obstruction, leading to urinoma formation (collection of extravasated urine).
• Irreversible Kidney Damage.

 

Prevention and When to Seek Medical Attention

Prevention of acquired hydronephrosis involves:

• Prompt treatment of conditions that can cause urinary obstruction (e.g., kidney stones, UTIs, BPH).
• Regular medical follow-up for individuals with known risk factors or congenital urinary tract anomalies.
• Maintaining good hydration to help prevent kidney stones.

Congenital hydronephrosis may be detected on prenatal ultrasound, allowing for early postnatal evaluation and management.

It is important to seek medical attention if you experience:

• Sudden onset of severe flank or abdominal pain.
• Pain accompanied by fever, chills, nausea, or vomiting.
• Visible blood in the urine.
• Difficulty urinating or changes in urinary habits.
• Unexplained persistent flank discomfort or a palpable mass in the abdomen/flank.

Early diagnosis and treatment of the underlying cause of hydronephrosis or pyonephrosis are crucial for preserving kidney function and preventing serious complications.