1. Renal parenchymal abscess: Solitary or multiple abscesses are most frequently a complication of pyelonephritis in patients with coexisting vesicoureteral reflux or urinary obstruction. A computed tomography (CT) scan is the imaging study of choice. Early antibiotic treatment may achieve complete recovery, but larger or not resolving abscesses may require surgical intervention—most frequently drainage, rarely partial or complete nephrectomy.
2. Multiple renal cortical abscesses develop as a result of hematogenous spread from a distant infection site (most frequently skin, bone, or endocardial infection) that is undetectable in approximately one-third of patients at the time of the diagnosis of renal involvement. In 90% of patients, Staphylococcus aureus is identified as the etiologic agent. Microabscesses form in the renal cortex and then coalesce into larger abscesses, which may occasionally spontaneously drain into the renal collection system. Blood and urine cultures are usually negative. A CT scan is the imaging study of choice.
Treatment: Antibiotics and surgical procedures as in renal parenchymal abscess.
3. Perinephric abscess refers to an accumulation of purulent exudate between the renal capsule and the renal fascia. It may be caused by pyonephrosis (see below; particularly in the course of nephrolithiasis) or by pyelonephritis complicated by renal parenchymal abscess or renal cortical abscesses; hematogenous spread is rare. Patients with diabetes mellitus account for approximately a quarter of all cases. The clinical manifestations include fever, rigors, flank pain, sometimes also a palpable mass in the lower back. Blood cultures are positive in 10% to 40% of patients. A CT scan is the imaging study of choice (ultrasonography results are false negative in ~30% of cases).
Treatment: Surgical or percutaneous drainage in combination with targeted antibiotic therapy based on the culture results (urine, blood, and abscess contents).
4. Pyonephrosis (pus collected in renal pelvis) usually develops as a result of an ascending infection in patients with hydronephrosis, frequently as a complication of nephrolithiasis.
Treatment: Urologic intervention.
5. Emphysematous pyelonephritis is a severe multifocal bacterial infection that leads to necrosis and production of gas in the renal parenchyma or perinephric tissues. Approximately 95% of cases involve patients with diabetes mellitus and coexisting impaired urine flow; women are more frequently affected than men. Emphysematous pyelonephritis manifests clinically as particularly severe pyelonephritis with features of septic shock. Sometimes physical examination reveals crackles over the affected area. Emphysematous pyelitis is a milder form of the disease, with the production of gas limited to the pyelocalyceal system. Imaging studies reveal the presence of gas.
Treatment: Surgical drainage and antibiotic therapy, and nephrectomy when necessary. Despite therapeutic interventions, the mortality rates are high and range between 11% to 42%.
6. Renal papillary necrosis: Ascending infection may lead to necrosis of the renal papillae and their sloughing into the pyelocalyceal system. The sloughed papillae may cause renal colic. Papillary necrosis affects predominantly patients with coexisting diabetes mellitus. The clinical manifestations are similar to severe acute pyelonephritis.
Treatment: Antibiotics are usually effective; invasive procedures are necessary in the case of urinary obstruction by necrotic tissues.
7. Chronic pyelonephritis: Chronic tubulointerstitial nephritis caused by chronic or recurrent kidney infections. This almost exclusively affects patients with significant anatomic abnormalities of the urinary tract, such as urinary obstruction, staghorn kidney stones, or vesicoureteral reflux (the most frequent cause of chronic pyelonephritis in children). A characteristic feature is focal scarring of the renal parenchyma causing a rough surface of the kidney on imaging studies. The disease may be limited to one kidney. With time, patients develop progressive fibrosis, tubular atrophy, glomerular sclerosis, and glomerular atrophy. The dominant clinical features are the signs and symptoms of recurrent urinary tract infection (UTI) (see Urinary Tract Infections), and in the case of severe renal impairment, features of chronic renal failure. Urinalysis usually reveals leukocyturia, occasionally with white blood cell casts. Negative culture results do not exclude the diagnosis of chronic pyelonephritis. Proteinuria (usually <2 g/d) is indicative of progressive renal impairment. Ultrasonography usually reveals small kidneys, sometimes with a rough surface, as well as features of the underlying condition (kidney stones, urinary obstruction). Urography shows deformations of some or all renal calices (widening, blunting). Renal scintigraphy has the highest sensitivity for detecting parenchymal scarring. Voiding cystography may be helpful in detecting vesicoureteral reflux.
Treatment includes management of the underlying condition and slowing the progression of chronic kidney disease.
8. Xanthogranulomatous pyelonephritis is a severe chronic renal parenchymal infection, which leads to kidney damage and perirenal fibrosis. It is almost always caused by chronic urinary obstruction, and three-quarters of patients have concomitant staghorn stones and chronic or recurrent UTI symptoms. The clinical presentation is typical for chronic inflammation, with recurrent fever, lower back pain, and weight loss. Exacerbations manifest as severe UTI and may lead to the development of cutaneous or intestinal fistulas if left untreated. Usually the diagnosis is made following nephrectomy, which is often performed due to misdiagnosed renal cancer. A CT scan is the imaging study of choice. Ultrasonography findings revealing large kidneys with staghorn stones may suggest xanthogranulomatous pyelonephritis.
9. Acute prostatitis is almost always caused by pathogens ascending from the urethra. It may be accompanied by urethritis or UTI. The most frequent etiologic agents are Enterobacteriaceae and other pathogens causing urethritis. Clinical features include rapidly increasing fever, pelvic or perineal pain, dysuria, and cloudy urine. Prostatic edema may cause urinary retention. When examined by palpation (this should be done gently due to the risk of causing bacteremia), the prostate is swollen, soft, warm, and very tender. Urine cultures should be performed in every patient. Blood cultures should be obtained in all hospitalized patients (these are positive in 20% of patients).
Treatment: Same as in complicated UTI. Once culture results are available, modify the treatment if necessary. Acute prostatitis is usually treated for 2 (maximum 4) weeks; in patients with chronic prostatitis, treatment is extended to 4 (maximum 6) weeks. Lack of improvement after one week of treatment may suggest prostatic abscess.
10. Acute epididymitis is the most frequent cause of the so-called acute scrotum in adult male patients. Infection is the result of reflux of infected urine from the prostatic segment of the urethra through the spermatic cord into the epididymis. In young men, the most common etiologic agents are Chlamydia trachomatis and Neisseria gonorrhoeae (sexually transmitted diseases), while in older patients the incidence of infections with Enterobacteriaceae increases. One-sided scrotal pain is a characteristic symptom of acute epididymitis; it may be accompanied by fever and rigors, dysuria, or signs and symptoms of acute prostatitis. Physical examination reveals inflamed, swollen, and very tender epididymis. Orchitis may occur later in the course of the disease and lead to the development of hydrocele.
Treatment: Empiric therapy should be started before receiving microbiology results (culture, nucleic acid amplification test) and should be adjusted once the results become available. Empiric treatment of patients <35 years must cover Neisseria gonorrhoeae and Chlamydia trachomatis: a single dose of IM ceftriaxone 250 mg and doxycycline 100 mg bid for 10 days. Because Enterobacteriaceae are much more common in patients >35 years, empiric treatment consists of starting IV ceftriaxone 2 g once daily. A single-dose treatment is sufficient for the treatment of epididymitis due to N gonorrhea or C trachomatis (see Urethritis), while the duration of treatment of epididymitis caused by Enterobacteriaceae is 10 to 14 days.
11. Urosepsis: see Sepsis and Septic Shock.