Anthony J. Tracey, MD, MPH
Raju Thomas, MD, MHA, FACS
BASICS
DESCRIPTION
• Pyonephrosis is a collection of purulent material in the renal collection system
• Typically resulting from an underlying obstruction within the upper urinary tract (2)
– With concomitant urinary tract infection
• Considered a surgical emergency with drainage of obstructed collecting system necessary (1)
EPIDEMIOLOGY
Incidence
• True incidence is unknown
• Increased in patients with upper urinary tract obstruction
Prevalence
See above
RISK FACTORS
• Upper urinary tract obstruction
• History of prior urologic instrumentation
• Immunocompromised patient
• Diabetes mellitus
• Chronic UTIs
Genetics
None
PATHOPHYSIOLOGY
• Etiologies of obstruction (1)
– Stones and staghorn calculi: In as many as 75% of patients
– Mucinous adenocarcinoma of the renal pelvis
– Pregnancy
– Fungus balls
– Metastatic retroperitoneal fibrosis—eg, renal tumors, testicular cancer, colon cancer
– Obstructing transitional cell carcinoma
– Ureteropelvic junction obstruction (UPJO)
– 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
– Ectopic ureter with ureterocele
– Neurogenic bladder
• Infectious agents (in decreasing order of incidence) (1)
– Escherichia coli
– Enterococcus species
– Candida species and other fungal infections
– Enterobacter species
– Klebsiella species
– Proteus species
– Pseudomonas species
– Bacteroides species
– Staphylococcus species
– Methicillin-resistant Staphylococcus aureus (MRSA)
– Salmonella species
– Tuberculosis (causes both infection and strictures) (2)
ASSOCIATED CONDITIONS
• Nephrolithiasis (most common) (1)
• UPJO
• Urothelial carcinoma (UC) of the upper tracts
• Pyelonephritis
• Emphysematous pyelonephritis/pyelitis
• Xanthogranulomatous pyelonephritis (XGP)
• Ureteral stricture (2)
GENERAL PREVENTION
• Relief of underlying urologic obstruction
• Proper medical management of immunosuppression
• Identification of any anatomic urologic abnormality (ie, horseshoe kidney)
ALERT
Patients may rapidly decline clinically and become septic.
DIAGNOSIS
HISTORY
• Fever
• Flank pain
• Clinical evidence of UTI
PHYSICAL EXAM
CVA tenderness with or without palpable abdominal mass (hydronephrotic kidney)
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Pyuria
• Elevated white count (less specific)
• Bacteriuria (less specific)
• Urine culture of obstructed system
• Elevated C-reactive protein
– 1 study showed CRP levels >28 mg/L with flank pain a reliable indication for emergent decompression (1)
Imaging
• CT scan with IV contrast (2)
– Diagnostic criteria for pyonephrosis
Increased wall thickness of the renal pelvis ≥2 mm
The presence of renal pelvic contents and debris
Parenchymal and perirenal findings, such as perirenal fat stranding (3)
• Ultrasonography (US)
– Sensitivity of renal US for differentiating hydronephrosis from pyonephrosis is 90%, and the specificity is 97% (1)
Debris
Low-level echogenic foci
Hydronephrosis
• MRI
– Use increasing for inflammatory disorders of the GU tract
Diffusion MRI shows hyperintense collecting system for pyonephrosis and hypointense signal for simple hydronephrosis
May be useful for patients with impaired renal function (3)
• Renal nuclear scan
– Useful in assessing renal function after decompression and to evaluate if involved renal unit is salvageable
– Not helpful in the immediate diagnostic period
Diagnostic Procedures/Surgery
• Once pyonephrosis has been diagnosed, there are two possible initial interventions:
– Antegrade nephrostomy tube placement
– Retrograde ureteral stent placement
Pathologic Findings
• Aspiration of obstructed system will usually show:
– WBCs
– Bacteria or fungus
– Sloughed urothelial cells
DIFFERENTIAL DIAGNOSIS
• Nephrolithiasis/urolithiasis
• Xanthogranulomatous pyelonephritis
• Ureteropelvic junction obstruction (UPJO)
• Urothelial carcinoma (UC) of upper tracts
• Ureteral stricture
• Extrinsic obstruction with hydronephrosis (malignancy, retroperitoneal fibrosis)
TREATMENT
GENERAL MEASURES
• Drainage of obstructed collecting system is the mainstay of treatment
– Antegrade nephrostomy tube placement
Indicated in the clinically unstable patient
Best for maximal decompression
– Retrograde ureteral stent placement
Indicated in the stable patient able to tolerate general anesthesia
Relatively contraindicated in setting of a large upper tract stone that will eventually need percutaneous therapy or fungus ball
• Treatment of source obstruction:
– Once collecting system has been decompressed and appropriate antibiotic/antifungal therapy has been given for 2 wk
– May include endoscopic, percutaneous, transurethral, laparoscopic, robotic, extracorporeal, or open approaches
– Depends on the nature of obstruction (ie, stone, stricture) (1)
– Clinical feasibility of intervention
MEDICATION
First Line
• Broad spectrum intravenous antibiotics (ie, piperacillin and tazobactam, gentamicin, and ampicillin) and antifungals if clinically indicated for funguria
– Antibiotics can be focused once cultures result
Second Line
N/A
SURGERY/OTHER PROCEDURES
• Indication for nephrectomy is controversial
– May be indicated if source of infection is not found
– Help to exclude malignant etiology of obstruction
– Lack of response to percutaneous drainage and IV antibiotics/antifungals
– Poorly functioning kidney
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
N/A
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
• Good in patients who receive prompt diagnosis and therapy
• Most patients will improve 24–48 hr after drainage of obstructed renal collecting system
• Recovery of renal function is rapid
COMPLICATIONS
• Sepsis is the most common complication of delayed treatment
• Other complications of delayed treatment include:
– Rupture of pyonephrotic kidney resulting in:
Generalized peritonitis
Renocolic fistula
Renoduodenal fistula
Renocutaneous fistula
Splenic rupture
– Rare complications:
Pneumoperitoneum
Renal vein thrombosis
Psoas abscess
Perinephric abscess
Rhabdomyolysis
– Loss of renal function
• Complications from nephrostomy tube:
– Blood transfusions
– Hematoma
– Nephrostomy tube replacement/revision
• Increased risk of infection if nephrectomy is not performed when indicated.
FOLLOW-UP
Patient Monitoring
• Treatment of underlying obstruction (ie, calculus, stricture, malignancy)
• Treatment and control of any predisposition to infection (ie, DM, HIV/AIDS, neurogenic bladder)
Patient Resources
• http://kidney.niddk.nih.gov/kudiseases/pubs/stonesadults/
• http://www.medicinenet.com/kidney_stone/article.htm
• http://www.mayoclinic.com/health/kidney-stones/DS00282
REFERENCES
1. Peterson AC. “Pyonephrosis” Medscape Article 2013; emedicine.medscape.com/article/440548
2. Raynor MC, Carson CC. Urologic issues for the internist urinary infections in men. Med Clin North Am. 2011;95:43–54.
3. Hammond NA, et al. Genitourinary imaging infectious and inflammatory diseases of the kidney. Rad Clin North Am. 2012;50:259–270.
ADDITIONAL READING
Schaeffer AJ, Schaeffer EM. Infections of the urinary tract. In: Wein AJ, et al. eds. Campbell-Walsh Urology. 10th ed. Philadelphia: Saunders; 2012.
See Also (Topic, Algorithm, Media)
• Fungal Infections, Genitourinary
• Hydronephrosis/Hydroureteronephrosis, (Dilated Ureter/Renal Pelvis), Adult
• Pyonephrosis Image 
• Ureter, Obstruction
• Urosepsis
• Urolithiasis, Staghorn
CODES
ICD9
• 590.80 Pyelonephritis, unspecified
• 593.89 Other specified disorders of kidney and ureter
• 599.0 Urinary tract infection, site not specified
ICD10
• N13.6 Pyonephrosis
• N28.89 Other specified disorders of kidney and ureter
• N39.0 Urinary tract infection, site not specified
CLINICAL/SURGICAL PEARLS
• Patients with pyonephrosis may be asymptomatic or present with a picture of an abscess with fever and chills.
• Urolithiasis, staghorn calculi, and fungus balls are the most common clinical causes of pyonephrosis.