AUTHOR AND EDITOR INFORMATION

Section 1 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

INTRODUCTION

Section 2 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Pyonephrosis refers to infected purulent urine in an obstructed collecting system. Similar to an abscess, it is typically associated with fever, chills, and flank pain, although some patients may be asymptomatic. Pyonephrosis may develop from a broad spectrum of pathologic conditions involving either an ascending infection of the urinary tract or the hematogenous spread of a bacterial pathogen. Urinary obstruction in the presence of pyelonephritis may lead to a collection of WBCs, bacteria, and debris in the collecting system and subsequently result in pyonephrosis. In this situation, with the accompanying "pus under pressure," patients may deteriorate rapidly and become septic. Thus, early recognition and treatment of acute infections of the kidney, especially in patients with suspected urinary tract obstruction, are of paramount importance.

Problem

If not recognized early, patients with pyonephrosis may rapidly deteriorate and develop septic shock. In addition to the morbidity and mortality of septic shock, potential complications of delayed diagnosis and treatment include irreversible damage to the kidneys with possible need for nephrectomy. Even in the modern era of antibiotics, adequately controlling an overwhelming infection in an obstructed renal unit without surgical intervention may be impossible. If the diagnosis is delayed unduly, death may result.

Frequency

This disorder is relatively uncommon, and the true incidence of development with other renal infections is not reported; however, it can commonly occur in patients with upper urinary tract obstruction from a variety of causes (eg, stones, tumors, ureteropelvic junction [UPJ] obstruction).

Etiology

Upper urinary tract infection in combination with obstruction and hydronephrosis may lead to pyonephrosis. This may progress to renal and perirenal abscesses. Risk factors for developing pyonephrosis include immunosuppression from medications (eg, steroids), disease (eg, diabetes mellitus, AIDS), and any anatomic urinary tract obstruction (eg, stones, tumors, UPJ obstruction, pelvic kidney, horseshoe kidney). Fungal infections are commonly associated with patients who are immunocompromised or those treated with long-term antibiotics. When fungus balls are present, they may obstruct the renal pelvis or the ureter, resulting in pyonephrosis. Xanthogranulomatous pyelonephritis, a clinical condition consisting of upper renal calculus and infection, has been reported to progress to pyonephrosis when obstruction is present.

Pyonephrosis is uncommon in adults, rare in children, and thought to be extremely rare in neonates. Recently, however, pyonephrosis has been reported in several neonates as well as adults, making clear that pyonephrosis may develop in any age group.

The disease process of pyonephrosis consists of 2 parts: infection and obstruction.

Infection

Multiple infectious agents are reported in the current literature. These include the following in decreasing order of incidence:

• Escherichia coli
• Enterococcus species
• Candida species and other fungal infections
• Enterobacter species
• Klebsiella species
• Proteus species
• Pseudomonas species
• Bacteroides species
• Staphylococcus species
• Salmonella species
• Tuberculosis (causes both infection and strictures)

Obstruction

The etiology of the obstruction may relate to any of the following factors:

• Stones and staghorn calculi in as many as 75% of patients
• Fungus balls
• Metastatic retroperitoneal fibrosis (eg, renal tumors, testicular cancer, colon cancer)
• Obstructing transitional cell carcinoma
• Pregnancy
• UPJ obstruction
• Obstructing ureterocele
• Ureterovesical junction obstruction
• Chronic stasis of urine and hydronephrosis secondary to neurogenic bladder
• Ureteral strictures
• Papillary necrosis
• Tuberculosis
• Duplicated kidneys with obstructive components
• Neurogenic bladder
• Other rare causes such as sciatic hernias causing ureteral obstruction

Pathophysiology

Purulent exudate collects in a hydronephrotic collecting system and forms an abscess. This purulent exudate consists of inflammatory cells, infectious organisms, and a necrotic sloughed urothelium. This becomes walled off and protected from the body's natural immune system and antibiotics. If not recognized and treated promptly, this infectious process may progress, often resulting in clinical deterioration of the patient with urosepsis, which can occur swiftly.

Clinical

Patients with pyonephrosis may present with clinical symptoms ranging from asymptomatic bacteruria (15%) to frank sepsis. Maintain a high index of suspicion when examining a patient with a history of fever, flank pain, evidence of a urinary tract infection, and obstruction or hydronephrosis. On physical examination, a palpable abdominal mass may be associated with the hydronephrotic kidney.

INDICATIONS

Section 3 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

The presence of pyonephrosis is a surgical emergency and needs immediate intervention. Pyonephrosis may be treated with either an antegrade or a retrograde decompression. An indication for retrograde decompression, or placement of a ureteral stent, is a stable patient with no signs of hemodynamic instability. Intravenous antibiotics must be given prior to stent placement in a stable patient; after this is done, retrograde decompression may be safely undertaken. Disadvantages of retrograde decompression include lack of antegrade access for radiologic studies, smaller-caliber urinary drainage catheter than with percutaneous access, increased irritative urinary symptoms, inability to administer medications such as antibiotics via nephrostomy tube, and limitation of percutaneous chemolysis that may cause dissolution of any stones. To maximize drainage, a urethral catheter should be left in place after stent placement.

A retrograde approach usually requires a general anesthetic, and bypassing the obstruction may not be possible in some patients. In addition, the risk of pyelovenous, pyelolymphatic, and pyelosinus backflow of infected urine into the systemic circulatory system always exists with retrograde manipulation. This may result in iatrogenic sepsis and patient decompensation.

Definitive management of stones and obstruction with ureteroscopy, lithotripsy, or endopyelotomy is contraindicated in the immediate treatment of patients with pyonephrosis. If retrograde stent placement is chosen, the surgeon should attempt to minimize instrumentation and retrograde pyelography as much as possible and decompress the obstruction with minimal trauma to the urinary tract. Recently, reports exist of ureteroscopic instrumentation involving stone and obstruction removal during active infection. Although performed at some institutions, the authors do not recommend this practice because it may result in sepsis and worsening infection.

Antegrade treatment with percutaneous nephrostomy tube placement is indicated in any patient with hemodynamic instability or sepsis and when retrograde instrumentation may cause an inappropriate delay in treatment or unnecessary trauma to the genitourinary tract. While some believe this technique to be more invasive, placement of a nephrostomy tube has certain advantages. It allows administration of medication to treat difficult infections directly to the collecting system and ureter, stones may sometimes be dissolved chemically with antegrade irrigation, and it allows antegrade treatment of obstructing stones. Antegrade radiographic studies often help with treatment planning once the patient is stable. Most importantly, it allows drainage of an infected renal unit with minimal trauma or risk to the patient, and it avoids the additional risks of a general anesthetic.

Disadvantages to nephrostomy tube placement include the possibility of renal trauma and difficulties in placing the tube in some patients because of body habitus or mild hydronephrosis that makes localization with ultrasonography difficult.

With pyonephrosis, nephrostomy tubes should never be placed transpleurally. This avoids pneumothorax, pleural infections, and empyema formation.

Percutaneous suprapubic tube placement guided by ultrasonography or radiography can be helpful in selected patients with urosepsis due to bladder outlet obstruction when a Foley catheter cannot be easily placed.

RELEVANT ANATOMY

Section 4 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

See Pathophysiology.

CONTRAINDICATIONS

Section 5 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Retrograde placement of a ureteral stent is contraindicated in an unstable patient with sepsis. In these situations, proceeding directly with percutaneous placement of a nephrostomy tube is best for maximal decompression of the infected system. The retrograde stent placement is relatively contraindicated in patients with known impacted and obstructing upper tract stones that may ultimately need percutaneous treatment or in those with fungus balls that may need additional therapy with antegrade irrigation and instrumentation.

WORKUP

Section 6 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Lab Studies

• Complete blood cell count with a manual differential, serum chemistry with BUN and creatinine, a urinalysis with culture, and blood cultures are indicated in the initial workup of a patient suspected of having pyonephrosis. A urine culture of the fluid above the obstruction must be obtained in order to guide antibiotic therapy. A culture specimen may be obtained from an open-ended catheter that has been advanced above the obstruction during stent placement. Cultures should also be obtained from the percutaneous tube at the time of nephrostomy placement if this course of action is chosen.
• • Leukocytosis and bacteruria may be present; however, they are not specific for pyonephrosis and may be from other causes without pyonephrosis (eg, pyelonephritis, uncomplicated urinary tract infections).
  • Pyuria, while often present in pyonephrosis, is nonspecific. Bacteruria, fever, pain, and leukocytosis can be absent in 30% of patients with pyonephrosis.

Imaging Studies

• Routine radiographic imaging of patients with uncomplicated urinary tract infections is not generally advocated. However, appropriate radiographic studies are beneficial in diagnosing pyonephrosis, emphysematous pyelonephritis, and renal and/or perirenal abscess when patients do not improve rapidly with appropriate antibiotics.
• Ultrasonography
• • The sensitivity of renal ultrasonography for differentiating hydronephrosis from pyonephrosis is 90%, and the specificity is 97% (see Image 1).
  • Ultrasonographic findings suggestive of pyonephrosis include the presence of hydronephrosis in conjunction with debris in the collecting system. The presence of debris and layering of low-amplitude echoes in the hydronephrotic kidney are indicators of pyonephrosis. These low-level echogenic foci in the collecting system remain the most consistent finding in pyonephrosis. These findings are specific enough that their absence excludes pyonephrosis with a high degree of accuracy.
  • Echogenic gas is rarely demonstrated. Intrarenal gas appears as "dirty shadows." If echogenic gas is present, assume that the patient has a severe infection and possible renal injury suggestive of emphysematous pyelonephritis.
  • Ultrasonography does have drawbacks. For example, it may not always differentiate hydronephrosis from early pyonephrosis. In these cases, consider conducting an ultrasonographically guided aspiration of the hydronephrotic fluid for microscopic examination to establish the diagnosis.
• Computed tomography scanning
• • Computed tomography (CT) scanning is extremely helpful in diagnosing pyonephrosis. Advantages of CT scanning include definitive delineation of the obstruction, function of the kidney, and severity of hydronephrosis as well as the presence of other abdominal pathologies, including metastatic cancer, retroperitoneal fibrosis, and renal stones that are not observed on the ultrasonogram (see Image 2).
  • Diagnostic criteria for pyonephrosis on CT scanning include (1) increased wall thickness of the renal pelvis greater than or equal to 2 mm, (2) the presence of renal pelvic contents and debris, and (3) parenchymal and perirenal findings, such as perirenal fat stranding.
• Excretory urography
• • This study is seldom helpful in the diagnosis of pyonephrosis.
  • The decreased function of the affected kidney that accompanies active infection typically prevents visualization on contrast studies.
• Magnetic resonance imaging
• • MRI has recently been used extensively for imaging of inflammatory conditions of the genitourinary tract. Findings in pyelonephritis include renal enlargement with a heterogeneous appearance on T2-weighted images. Perirenal edema can be seen as well as areas of high signal intensity on T2-weighted images. A method to distinguish pyonephrosis from noninfected hydronephrosis has been proposed based on diffusion MRI. In this imaging study, pyonephrosis is correlated with marked hyperintense signals in the collecting system (which corresponds to the pus in the system), while the hydronephrotic kidney without pus is hypointense.

Other Tests

• Renal nuclear scanning
• • Renal nuclear scanning is not particularly helpful in the immediate diagnostic workup of pyonephrosis. Acutely, scans may exhibit prolonged cortical uptake with delayed excretion of radionuclide similar to that observed in acute obstruction. The image may also be similar to that observed in acute pyelonephritis with defects in uptake of the radiopharmaceutical that can be unifocal, multifocal, or diffuse. These defects often resolve with resolution of the infection; however, persistence in follow-up renal nuclear scans may indicate permanent damage to the renal cortex.
  • Renal nuclear scanning may be helpful when a kidney is believed to be nonfunctional on any imaging study during the acute phase of pyonephrosis. Performing follow-up nuclear imaging studies is prudent after resolution of the infection to establish the function of the involved kidney. If a kidney is proven to be nonfunctional after resolution of infection and treatment of the etiology of the obstruction, then nephrectomy may be indicated to prevent further episodes of pyonephrosis.
• Antegrade nephrostography
• • This test may be extremely helpful in determining the etiology of the obstruction associated with pyonephrosis and in planning further treatment strategies.
  • As with any invasive procedure, nephrostography should be delayed until the patient is stable, on antibiotics, and afebrile for 1-2 weeks after placement of a nephrostomy tube.
• Further imaging tests
• • When a definitive anatomic abnormality, such as a stone or tumor, cannot be determined, further imaging studies and tests may be needed to establish the etiology of the pyonephrosis.
  • These tests may include voiding cystourethrography to exclude vesicoureteral reflux, multichannel urodynamics to establish a possible neurogenic bladder with urine stasis, and serial renal ultrasonography to document resolution of hydronephrosis after treatment.

Diagnostic Procedures

• CT- and ultrasound-guided aspiration
• • Aspiration of the collecting system with CT or ultrasonographic guidance with Gram stain and culture of the fluid provides a definitive diagnosis of pyonephrosis.
  • Sending the culture for aerobic, anaerobic, and fungal pathogens is important.
  • If clinically indicated, perform acid-fast stain and send cultures for tuberculosis testing.

TREATMENT

Section 7 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Medical therapy

The treatment of pyonephrosis has changed dramatically over the years. Prior to the 1980s, emergency surgical excision with nephrectomy was the standard of care. However, this was associated with a high morbidity and complication rate, including sepsis, wound infections, peritonitis, and fistulas.

Initially, treat patients with appropriate intravenous antibiotics consisting of an aminoglycoside (gentamicin) and gram-positive coverage (ampicillin) prior to instrumentation. Depending on the clinical situation, additional anaerobic coverage with clindamycin may be needed. Be cognizant of the fact that patients may have fungal infection or tuberculosis. The use of antifungal or antibacterial agents is predicated upon culture results. Many patients are septic and may require aggressive fluid resuscitation with crystalloids. Pressor support (with dopamine) may be needed to maintain adequate blood pressure and hemodynamics.

Surgical therapy

With the advent of ultrasonography and CT scanning, percutaneous drainage has become the mainstay of treatment. It has low morbidity and mortality rates with an excellent outcome. CT- and ultrasound-guided drainage significantly decreases the need for nephrectomy, resulting in renal preservation.

Retrograde decompression of pyonephrosis in patients who are severely ill is not advocated because of the need for internal instrumentation and the possible future need for antegrade irrigation. In selected healthy stable patients, consider retrograde decompression as an option. This avoids placement of the percutaneous nephrostomy tube and allows internalization of the drainage catheter; however, it does not allow for antegrade medication infusion or treatment of obstruction that is sometimes needed with funguria and infected stones.

Consider treating these patients in the following 2 stages:

• Stage 1 (decompression and drainage)
• • Perform retrograde stent placement.
  • Use percutaneous CT- or ultrasound-guided nephrostomy.
  • The infectious process often resolves within 24-48 hours following drainage, and the patient may improve significantly once this occurs.
• Stage 2
• • Eliminate the obstruction by removing the stone, fungus ball, or tumor 1-2 weeks after percutaneous drainage or stent placement. Accomplish this with the use of electrohydraulic lithotripsy, laser lithotripsy, percutaneous nephrolithotomy, extracorporeal shock wave lithotripsy, endopyelotomy, transurethral resection, or open surgical procedures. All of these are based on the type of obstruction and clinical situation.
  • In patients with uric acid stones and fungus balls, antegrade irrigation with alkaline fluids and antifungals through the nephrostomy tube may be needed prior to surgical intervention.

COMPLICATIONS

Section 8 of 12  

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• Introduction
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• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Most patients do well after prompt diagnosis and treatment.

Sepsis is the most common complication in the perioperative period when treatment is delayed.

Generalized peritonitis can result from a rupture of the pyonephrotic kidney. In 1996, Hendaoui et al reported the first case of a splenic abscess that developed from a ruptured pyonephrosis after the development of generalized peritonitis. This occurrence was again reported by Sugiura et al in 2004, making it possibly much more common than originally thought.

Fistulas may develop and can be associated with peritonitis. Renocolonic, renoduodenal, and renocutaneous fistulas are the most common; therefore, suspect these in patients with continued electrolyte disorders, diarrhea, and recurrent urinary tract infections after resolution of pyonephrosis.

Other rare complications include pneumoperitoneum from lithogenic pyonephrosis, nephrobronchial fistula, renal vein thrombosis, psoas abscess and/or perinephric abscess, and rhabdomyolysis.

Delay in diagnosis and treatment may result in a loss of renal function from parenchymal damage.

Perinephric hematomas, blood transfusions, and the need for nephrostomy tube revision are also complications of percutaneous drainage. If a nephrectomy must be performed in the future, long-term nephrostomy tubes are reported to increase the risk of a postoperative wound infection.

OUTCOME AND PROGNOSIS

Section 9 of 12  

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• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Most infectious processes resolve within 24-48 hours and significantly improve after either nephrostomy or retrograde stent drainage of the infection. If pyonephrosis is recognized and treated promptly, recovery of the affected renal unit is rapid. Long-term complications are rare when managed promptly; however, injury to the functional renal unit, abscesses, fistulas, and scarring may occur when definitive therapy is delayed.

For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education article Urinary Tract Infections.

FUTURE AND CONTROVERSIES

Section 10 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Treatment of infections occurring from pyelonephritis and pyonephrosis are changing rapidly and dramatically. The persistent use of broad-spectrum antibiotics, an increase in the population of immunocompromised patients (eg, patients with AIDS, patients undergoing chemotherapy), and the evolution of multiple drug–resistant bacteria complicate the picture.

Rare organisms, multiple organism infections, and Candida species now are commonly associated with infected calculi. Antegrade percutaneous nephrostomy placement allows both drainage of purulent material and the antegrade infusion of antifungal medication and antibiotics to adequately treat these infections. Retrograde stent placement does not allow this form of therapy; therefore, many experts stress the importance of nephrostomy drainage rather than retrograde transurethral drainage for pyonephrosis. The authors currently prefer retrograde, stent drainage after loading the patient with broad-spectrum antibiotics, saving antegrade drainage for the patients that may require further intervention, as discussed above.

The need for nephrectomy after percutaneous nephrostomy drainage and antibiotic treatment is debated. Some advocate the need for removal if the source of obstruction is not clearly identified. This can help exclude the presence of a malignant etiology for the obstruction, such as transitional cell carcinoma of the renal pelvis. Nonresponsiveness to therapy and progression of disease after percutaneous drainage are additional indications for nephrectomy; however, current technology reflects that preserving the maximal number of renal units is prudent.

MULTIMEDIA

Section 11 of 12  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

Media file 1:  Ultrasonogram of the kidney showing hydronephrosis with the presence of debris and layering of low-level echogenic foci consistent with pyonephrosis.
	View Full Size Image
Media type:  Image

Media file 2:  Computed tomography scan with images through the kidneys showing dilation of the collecting system, increased renal pelvic wall thickness, and the presence of renal pelvic debris.
	View Full Size Image
Media type:  CT

REFERENCES

Section 12 of 12

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome And Prognosis
• Future And Controversies
• Multimedia
• References

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Article Last Updated: Sep 14, 2006