Pyelonephritis and Perinephric Abscess

Pyelonephritis is infection affecting the renal pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and nausea with vomiting. The chronic type depends on the underlying pathology. The diagnosis is established via clinical presentation, supported by laboratory findings (in blood and urine). Imaging studies are performed if severe illness is noted or there is no response to initial treatment (antibiotics). CT is the study of choice, given its ability to detect renal abnormalities associated with the infection, including the extent of the disease. Perinephric abscess is an infection involving the perinephric space between the kidney and Gerota’s fascia. Perinephric abscess can be an extension from pyelonephritis or from hematogenous spread of a systemic infection. The diagnosis is established via CT scan. The treatment includes antibiotics, with abscess drainage (which is both diagnostic and therapeutic).

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Definitions

  • Pyelonephritis is infection of the kidney ( pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis and parenchyma) or the upper urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract and is considered a complicated urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract infection ( UTI UTI Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections).
  • Perinephric abscess is an infection characterized by suppurative material (liquefaction) between Gerota’s fascia and the renal capsule.
    • Can extend into the psoas and transversalis muscles
    • Can extend into the peritoneal cavity
Uti ascending and hematogenous

Ascending hematogenous urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract infection

Image by Lecturio. License: CC BY-NC-SA 4.0

Types of pyelonephritis

Acute pyelonephritis is the sudden-onset infectious process and inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the kidney(s) from ascending infection or hematogenous spread of systemic infections.

  • Uncomplicated pyelonephritis: infection with typical presentation and without the risk factors listed for the complicated type.
  • Complicated pyelonephritis:
    • Associated with pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care
    • Uncontrolled diabetes
    • Kidney transplantations
    • Urinary anatomical abnormalities
    • Acute or chronic kidney failure
    • Hospital-acquired infection
    • Immunocompromised state 
  • Chronic pyelonephritis emerges from recurrent or continuing UTIs, often associated with major anatomic abnormalities.

Epidemiology

  • Acute pyelonephritis:
    • More common in females than in males
    • 15–17 cases per 10,000 females 
    • 3–4 cases per 10,000 males
  • Chronic pyelonephritis: 
    • Common in children
    • Associated with vesicoureteral reflux Vesicoureteral Reflux Vesicoureteral reflux (VUR) is the retrograde flow of urine from the bladder into the upper urinary tract. Primary VUR often results from the incomplete closure of the ureterovesical junction, whereas secondary VUR is due to an anatomic or physiologic obstruction. Vesicoureteral Reflux (VUR) disease, which is noted in 30%–40% of children with UTIs
    • More common in females
  • Perinephric abscess: 
    • Rare; accounts for approximately 0.02% of hospital admissions 
    • Approximately 75% due to complications of UTIs
    • 20%–60% associated with renal calculi

Etiology

Uropathogens

  • Gram-negative bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview
    • Escherichia coli Escherichia coli The gram-negative bacterium Escherichia coli is a key component of the human gut microbiota. Most strains of E. coli are avirulent, but occasionally they escape the GI tract, infecting the urinary tract and other sites. Less common strains of E. coli are able to cause disease within the GI tract, most commonly presenting as abdominal pain and diarrhea. Escherichia coli (most common):
      • Adheres to urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract
      • Has P fimbriae that interacts with the uroepithelial cells
    • Proteus Proteus Proteus spp. are gram-negative, facultatively anaerobic bacilli. Different types of infection result from Proteus, but the urinary tract is the most common site. The majority of cases are caused by Proteus mirabilis (P. mirabilis). The bacteria are part of the normal intestinal flora and are also found in the environment. Enterobacteriaceae: Proteus mirabilis
    • Klebsiella Klebsiella Klebsiella are encapsulated gram-negative, lactose-fermenting bacilli. They form pink colonies on MacConkey agar due to lactose fermentation. The main virulence factor is a polysaccharide capsule. Klebsiella pneumoniae is the most important pathogenic species. Klebsiella spp.
    • Citrobacter spp.
    • Pseudomonas Pseudomonas Pseudomonas is a non-lactose-fermenting, gram-negative bacillus that produces pyocyanin, which gives it a characteristic blue-green color. Pseudomonas is found ubiquitously in the environment, as well as in moist reservoirs, such as hospital sinks and respiratory equipment. Pseudomonas aeruginosa (seen in individuals who underwent procedures or had health care exposure)
  • Gram-positive bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview
    • Staphylococci
    • Enterococci
    • Group B streptococci
  • In some cases, fungi Fungi Fungi belong to the eukaryote domain and, like plants, have cell walls and vacuoles, exhibit cytoplasmic streaming, and are immobile. Almost all fungi, however, have cell walls composed of chitin and not cellulose. Fungi do not carry out photosynthesis but obtain their substrates for metabolism as saprophytes (obtain their food from dead matter). Mycosis is an infection caused by fungi. Mycology: Overview (e.g., Candida Candida Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). Candida/Candidiasis) and viruses ( adenovirus Adenovirus Adenovirus (member of the family Adenoviridae) is a nonenveloped, double-stranded DNA virus. Adenovirus is transmitted in a variety of ways, and it can have various presentations based on the site of entry. Presentation can include febrile pharyngitis, conjunctivitis, acute respiratory disease, atypical pneumonia, and gastroenteritis. Adenovirus) cause UTIs.

Risk factors for urinary tract infections Urinary tract infections Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections

Associated with the development of pyelonephritis and perinephric abscess:

  • Stasis and obstruction caused by: 
    • Benign prostatic hyperplasia Benign prostatic hyperplasia Benign prostatic hyperplasia (BPH) is a condition indicating an increase in the number of stromal and epithelial cells within the prostate gland (transition zone). Benign prostatic hyperplasia is common in men > 50 years of age and may greatly affect their quality of life. Benign Prostatic Hyperplasia (BPH) 
    • VUR
    • Medications that promote incomplete emptying of the bladder
    • Urethral stricture
    • Cystocele
    • Neurogenic bladder
  • Foreign body: 
    • Introduces pathogen, or 
    • Acts as a nidus of infection (e.g., catheter, instrumentation)
  • Conditions that cause decreased resistance to organisms, such as:
    • Diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus
    • Malignancy
    • Immunosuppression
    • Spermicide use
    • Estrogen depletion
    • Antimicrobial use
  • Other:
    • Trauma
    • Anatomic abnormalities
    • Female (urethra is shorter and the anal and genital regions are close)
    • Sexual activity
    • Menopause Menopause Menopause is a physiologic process in women characterized by the permanent cessation of menstruation that occurs after the loss of ovarian activity. Menopause can only be diagnosed retrospectively, after 12 months without menstrual bleeding. Menopause
    • Fecal incontinence
    • Chronic constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation in toddlers

Pathophysiology

Acute pyelonephritis

  • Initial process:
    • Starts when the vaginal introitus or urethral meatus is colonized by pathogens, often the fecal flora
    • These microorganisms ascend into the bladder, and acute pyelonephritis develops when the infection reaches the kidney(s).
      • Ascending infection introduces the microorganism to the upper urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract.
      • Instrumentation also predisposes to ascending infection. 
    • Infection also can come from bacteremia, when seeding of the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys takes place (seen in staphylococci). 
  • Histopathologic findings: 
    • Necrosis or abscess formation is noted within the parenchyma.
    •  Renal tissue infiltration by neutrophils, macrophages, and plasma cells
  • Complications:
    • Renal abscess, a walled-off cavity of infection, with large lesions (> 2 cm) seen in individuals with a delayed diagnosis of diabetes
    • Perinephric abscess
    • Renal failure
    • Sepsis

Chronic pyelonephritis

  • Chronic pyelonephritis can occur when infection is persistent or recurrent. 
  • Affected kidney marked by inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation and scarring:
    • Dilated, blunted calyces
    • Tubular thyroidization (tubules filled with colloid casts, like thyroid tissue)
    • Fibrosis and inflammatory infiltrates in interstitium
  • Predominant risk factors include:
    • Genitourinary tract anomalies 
    • Urinary tract obstruction Urinary tract obstruction Urinary tract obstruction (UTO) refers to the blockage of the urinary tract, which can occur anywhere in the urinary tract. Urinary tract obstruction can be acute or chronic, partial or complete, and unilateral or bilateral. Urinary tract obstruction can cause acute or chronic kidney disease. Urinary Tract Obstruction (such as enlarged prostate Prostate The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. Prostate and other Male Reproductive Glands or renal calculus)
    • VUR:
      • Primary: most common form of reflux, arising from incompetent or inadequate closure of the ureterovesical junction (UVJ)
      • Secondary: abnormally high voiding pressure does not close the UVJ (such as in posterior urethral valves)
  • Xanthogranulomatous pyelonephritis:
    • A variant of chronic pyelonephritis
    • Characterized by renal destruction by granulomatous tissue, which is believed to be from aberrant inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation
    • Usual setting is obstruction due to infected renal stones.
    • Commonly associated with Proteus Proteus Proteus spp. are gram-negative, facultatively anaerobic bacilli. Different types of infection result from Proteus, but the urinary tract is the most common site. The majority of cases are caused by Proteus mirabilis (P. mirabilis). The bacteria are part of the normal intestinal flora and are also found in the environment. Enterobacteriaceae: Proteus mirabilis and E. coli
    • Histopathologic changes show infiltration by lipid-laden macrophages.

Perinephric abscess

  • Also begins either from local infection or hematogenous spread
    • When the organism initially invades the kidney, there can be outward spread to the perirenal fat (usually in gram-negative organisms). 
    • Perinephric abscess also can form from a ruptured renal abscess.
    • The organism can come from the circulation (seen in staphylococcal infections) and seed the peritoneal fat and, in most cases, may not affect the kidney.
  • Risk factors include:
    • Diabetes
    • Pregnancy
    • Urinary tract abnormalities

Clinical Presentation

Clinical features of pyelonephritis

  • Acute pyelonephritis:
    • Classic triad of symptoms:
      • Fever
      • Costovertebral tenderness
      • Nausea/vomiting
    • Can be associated with symptoms of cystitis (but not always seen): 
      • Frequency
      • Urgency
      • Dysuria 
      • Suprapubic tenderness
    • Pediatric symptoms:
      • Poor feeding 
      • Failure to thrive Failure to Thrive Failure to thrive (FTT), or faltering growth, describes suboptimal weight gain and growth in children. The majority of cases are due to inadequate caloric intake; however, genetic, infectious, and oncological etiologies are also common. Failure to Thrive
    • Geriatric symptoms: 
      • Altered mental status 
      • Disorientation
  • Chronic pyelonephritis is associated with: 
    • History of acute pyelonephritis 
    • Recurrent episodes of fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, lethargy, flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and nausea

Clinical features of perinephric abscess

  • Insidious onset of:
    • Fever
    • Vague lumboabdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
    • Fatigue, sweats, and weight loss
  • Can have a palpable flank mass
  • Symptoms of a lower UTI UTI Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections are not typical.

Diagnosis

Pyelonephritis

  • Findings suspicious for pyelonephritis: fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, nausea/vomiting
  • Blood tests:
    • Possible ↑ serum creatinine 
    • Leukocytosis (CBC)
  • Urine studies:
    • Urinalysis:
      • Pyuria 
      • Bacteriuria
      • Hematuria
      • WBC casts (suggestive of renal origin of pyuria)
      • Nitrite: reflects + Enterobacteriaceae (e.g., E. coli)
    • Urine culture: growth supports diagnosis of infection and identifies etiologic organism
    • Pregnancy test, because pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care affects management choices
  • Imaging studies are often pursued if the infection is associated with severe illness or does not improve:
    • Ultrasonography (acute pyelonephritis):
      • Kidney may be diffusely or focally enlarged
      • Areas with edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema are hypoechoic.
      • If hemorrhage is present, the area affected is hyperechoic.
      • Can be normal
    • Ultrasonography (chronic pyelonephritis):
      • Renal scarring, atrophy, and/or cortical thinning
      • Retraction of the papilla from overlying scar leads to calyceal clubbing
      • Thickened and dilated calyceal system
      • Asymmetric kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys
    • CT (method of choice):
      • Detects an obstruction (e.g., stones causing hydroureter, hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis)
      • Identifies urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract anomalies 
      • Hypodense renal lesions due to ischemia can be seen.
    • MRI is an option if it is necessary to avoid use of contrast or radiation.
    • Other imaging studies:
      • Voiding cystourethrography: establishes presence and degree of VUR  
      • IV pyelography/urography: checks for anomalies and obstruction

Perinephric abscess

  • Findings of:
    • Fever, costovertebral tenderness
    • No response to treatment for pyelonephritis
    • Unexplained peritonitis, pelvic abscess, and empyema
  • Blood tests:
    • ↑ WBC
    • Elevated inflammatory markers
    • ↑ Creatinine and ↓ GFR 
    • Blood culture 
  • Urine studies: 
    • Urinalysis: 
      • Pyuria
      • WBC casts
      • Bacteriuria
      • May be negative if the abscess does not communicate with the collecting system
    • Urine culture: identifies the offending organism
  • Imaging: 
    • If presentation is nonspecific, plain radiography can be the initial test. Radiography may occasionally reveal suspicious findings.
      • Scoliosis Scoliosis Scoliosis is a structural alteration of the vertebral column characterized by a lateral spinal curvature of greater than 10 degrees in the coronal plane. Scoliosis can be classified as idiopathic (in most cases) or secondary to underlying conditions. Scoliosis with the concavity toward the affected kidney
      • Abdominal mass 
      • Kidney enlargement with indistinct outlines or undefined renal shadow 
      • Loss of psoas margin
      • Radiopaque calculus/calculi
    • Ultrasonography: can show a thick-walled perinephric abscess (hypoechoic or mixed echogenicity)
    • Abdominal CT with contrast:
      • Best imaging 
      • Shows an abscess in the perinephric space (attenuation of soft tissue or fluid)
      • Gas pockets may also be seen. 
      • Allows visualization of extension to adjacent structures
Axial ct image

Axial CT image through the upper pole of the right kidney showing perinephric abscess reaching posteriorly to the inferior vena cava.

Image: “Axial CT image through the upper pole of the right kidney showing perinephric abscess reaching posterior to IVC.” by Wani NA. License: CC BY 2.0

Management

Acute pyelonephritis

Management depends on the severity of the clinical presentation and risk factors for drug resistance:

  • Uncomplicated pyelonephritis (mild course or with hemodynamic stability):
    • Empiric treatment:
      • 1st choice: oral fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones such as ciprofloxacin or levofloxacin (not for children)
      • Alternative: cephalosporins Cephalosporins Cephalosporins are a group of bactericidal beta-lactam antibiotics (similar to penicillins) that exert their effects by preventing bacteria from producing their cell walls, ultimately leading to cell death. Cephalosporins are categorized by generation and all drug names begin with "cef-" or "ceph-." Cephalosporins (such as ceftibuten or cefpodoxime) or trimethoprim Trimethoprim The sulfonamides are a class of antimicrobial drugs inhibiting folic acid synthesize in pathogens. The prototypical drug in the class is sulfamethoxazole. Although not technically sulfonamides, trimethoprim, dapsone, and pyrimethamine are also important antimicrobial agents inhibiting folic acid synthesis. The agents are often combined with sulfonamides, resulting in a synergistic effect. Sulfonamides and Trimethoprim–sulfamethoxazole
    • Most cases can be managed on an outpatient basis.
    • Hospitalization is necessary if an affected individual is unable to maintain hydration or is severely ill.
  •  Complicated pyelonephritis or severe uncomplicated pyelonephritis: 
    • Hospitalization:
      • IV therapy
      • After clinical improvement → oral therapy
    • Empiric therapy options (no risk of multidrug resistance):
      • Ceftriaxone
      • Piperacillin–tazobactam
      • Ciprofloxacin or levofloxacin
    • Empiric therapy options (with risk for multidrug resistance):
      • Piperacillin–tazobactam
      • Meropenem, imipenem, or doripenem
      • If urine shows gram-positive cocci: vancomycin, daptomycin, or linezolid
    • For critically ill individuals (requiring intensive care): vancomycin + antipseudomonal carbapenem Carbapenem The carbapenems and aztreonam are both members of the bactericidal beta-lactam family of antibiotics (similar to penicillins). They work by preventing bacteria from producing their cell wall, ultimately leading to bacterial cell death. Carbapenems and Aztreonam

Chronic pyelonephritis

  • Treatment of underlying cause (e.g., urology consult for obstruction)
  • For recurrent infections, long-term antibiotic therapy is an option.
  • Xanthogranulomatous pyelonephritis is treated with nephrectomy (partial or full) after initial antibiotic treatment.

Perinephric abscess

  • Antibiotics (choice depends on the suspected pathogenesis):
    • If associated with pyelonephritis, therapy targets Enterobacteriaceae.
    • If associated with staphylococcal systemic infection, therapy targets this etiologic agent.
  • Drainage:
    • If abscess is small (e.g., < 3 cm), antibiotic may be enough (especially if other specimens provide sufficient information regarding etiology)
    • Percutaneous drainage is done for diagnostic (especially if other specimens are not available) and therapeutic purposes.
    • Larger abscesses and/or failures to resolve with antibiotics require surgical intervention.

Differential Diagnosis

  • Acute appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the vermiform appendix. Acute appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis can also present with fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever and pyuria. The pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain of appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis is typically localized in the RLQ, not the costophrenic angle. Diagnosis can be confirmed with imaging (CT scan).  
  • Acute cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis: like pyelonephritis, acute cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis is more common in women and may present with fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever and abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain. However, in acute cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis, the pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain is localized in the RUQ, not the costophrenic angle. Also, urinalysis in the case of pyelonephritis shows bacteriuria, which can help differentiate it from cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis
  • Pancreatitis: can present with fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever and abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, but the pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain is localized in the epigastrium, not the costophrenic angle. Laboratory studies help distinguish these conditions: the urinalysis in pyelonephritis shows abnormalities such as bacteriuria and pyuria,  and pancreatitis is associated with elevated amylase and lipase. 
  • Lower UTI UTI Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections: can coexist with pyelonephritis. Lower UTIs usually are not associated with flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain and are generally shorter in duration. Similar organisms lead to lower and upper UTIs; thus, antibiotics targeting these etiologic agents cover both lower UTI UTI Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections  and pyelonephritis. 
  • Renal abscess: collection of suppurative material within the renal parenchyma. Renal abscess is usually associated with VUR and urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract obstruction from a stone. Differentiation from perinephric abscess is achieved with imaging studies (e.g., CT scan).
  • Urinoma: mass or encapsulated collection of extravasated urine. Urinoma arises from urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract injury or from spontaneous rupture secondary to urinary obstruction.  Urinoma can be differentiated from perinephric abscess by imaging studies, which include ultrasonography, CT, and MRI.

References

  1. Barshak M, Kasper DL. (2018). Intraabdominal infections and abscesses. Chapter 127 of Jameson J, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J (Eds.), Harrison’s Principles of Internal Medicine, 20th ed. McGraw-Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=2129&sectionid=186949739
  2. Belyayeva M, Jeong JM. (2021). Acute pyelonephritis. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK519537/
  3. Hooton T, Gupta K. (2021). Acute complicated urinary tract infection (including pyelonephritis) in adults. UpToDate. Retrieved July 25, 2021, from https://www.uptodate.com/contents/acute-complicated-urinary-tract-infection-including-pyelonephritis-in-adults
  4. Lohr, J. (2019). Chronic pyelonephritis. Medscape. Retrieved July 25, 2021, from https://emedicine.medscape.com/article/245464-overview
  5. Meyrier, A. (2021). Renal and perinephric abscess. UpToDate. Retrieved July 25, 2021, from https://www.uptodate.com/contents/renal-and-perinephric-abscess?topicRef=16109&source=related_link#H1492726249 
  6. Okafor CN, Onyeaso E.E. (2020). Perinephric abscess. StatPearls. Retrieved July 28, 2021, https://www.ncbi.nlm.nih.gov/books/NBK536936/

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