Urinary tract obstruction in the presence of pyelonephritis may lead to the collection of white blood cells (WBCs), bacteria, and debris in the collecting system, which may 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.
Similar to an abscess, pyonephrosis is typically associated with fever, chills, and flank pain, although some patients may be asymptomatic. Pyonephrosis may be caused by a broad spectrum of pathologic conditions involving either an ascending infection of the urinary tract or the hematogenous spread of a bacterial pathogen.
Risk factors for pyonephrosis include immunosuppression due to medications (eg, steroids), disease (eg, diabetes mellitus, acquired immunodeficiency syndrome [AIDS]), and any anatomic urinary tract obstruction (eg, stones, tumors, ureteropelvic junction [UPJ] obstruction, pelvic kidney, horseshoe kidney).
Pyonephrosis is uncommon in adults and rare in children, and it is thought to be extremely rare in neonates. However, pyonephrosis has been reported in several neonates [2] and adults, making it clear that the condition may develop in any age group.
The true incidence of development of pyonephrosis with other renal infections is not reported. However, the risk of pyonephrosis is increased in patients with upper urinary tract obstruction secondary to various causes (eg, stones, tumors, ureteropelvic junction [UPJ] obstruction).
In pyonephrosis, purulent exudate—consisting of inflammatory cells, infectious organisms, and a necrotic, sloughed urothelium—collects in a hydronephrotic collecting system and forms an abscess. The exudate becomes walled off and protected from the body's natural immune system and from 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.
With the advent of ultrasonography and computed tomography (CT) scanning, drainage—either percutaneously or retrograde with a ureteral stent—has become the mainstay of treatment. [5, 6, 7] Drainage has low morbidity and mortality rates and an excellent outcome. Drainage guided by CT scan or ultrasonography significantly decreases the need for nephrectomy, resulting in renal preservation.
In selected healthy, stable patients, consider retrograde decompression with a stent as an option. This avoids placement of a percutaneous nephrostomy tube and allows internalization of the drainage catheter. However, it does not allow for the antegrade medication infusion or the treatment of obstruction that is sometimes needed with funguria and infected stones.
When indicated, laparoscopic nephrectomy for inflammatory kidney disorders such as pyonephrosis has been shown to be safe and effective. The largest risk to the patient in these cases is typically the need to convert to an open procedure (28%) and wound infections.