A purulent infection located in the perinephric space between the kidney and the . It is typically secondary to acute pyelonephritis but may also be caused by the hematogenous spread of bacteria from elsewhere in the body (e.g., in individuals who inject drugs). Risk factors include diabetes mellitus, pregnancy, and urinary tract obstruction or abnormalities. Perinephric abscess typically has an insidious onset, with nonspecific symptoms that include flank or abdominal pain, fever, chills, and dysuria. Costovertebral angle tenderness is often present on examination. Abdominal CT is the preferred method for confirming the diagnosis. Abscess drainage and antibiotic therapy are the cornerstones of treatment. Antibiotic therapy alone may be considered in select patients with small abscesses (< 3 cm). Complications include extension of the abscess beyond the Gerota fascia, into the retroperitoneum (paranephric abscess), then sepsis.is a
Route of infection
- Most commonly due to local spread of infection in patients with acute pyelonephritis
- Hematogenous spread of infection from elsewhere in the body
- Risk factors
Onset is often insidious and symptoms are nonspecific, but they may include:
- Suspect perinephric abscess in patients with:
- Obtain imaging of the abdomen to confirm the diagnosis.
- Obtain cultures (blood, urine, drainage if possible) to identify the pathogen and guide treatment.
Perinephric abscess is only correctly diagnosed on presentation in approximately one-third of patients. A low threshold for imaging is recommended. 
Laboratory studies 
Routine laboratory studies are not required for diagnosis but may show the following nonspecific findings.
- Routine studies
- retroperitoneum and
CT abdomen and pelvis with contrast (preferred)
- Findings 
- MRI abdomen: indications and findings similar to CT
There is limited recent, high-quality literature on the management of perinephric abscess. Treatment decisions should be made in consultation with urology, interventional radiology, and infectious diseases.
- Arrange abscess drainage as indicated for most patients.
- Start intravenous empiric antibiotic treatment as soon as possible, ideally after obtaining cultures.
- Identify and treat underlying diseases and risk factors, e.g.:
- Nephrectomy may be required in some patients with persistent infection and extensive kidney damage. 
Antibiotic treatment 
Most recommendations are based on early studies; choose treatment in consultation with a specialist.
- gram-negative organisms (including Enterobacteriaceae) and S. aureus should cover common pathogens, i.e.,
- Switch to directed antibiotics once culture results are available.
- Determine the duration of antibiotic treatment based on clinical response.
Perinephric abscess drainage 
- Indicated for most patients for diagnostic and therapeutic purposes.
- Antibiotic treatment alone may be sufficient for the treatment of small abscesses (< 3 cm). 
- Preferred method: ultrasound) (guided by CT or
- Surgical drainage may be indicated in certain situations, e.g.: