A perinephric abscess is a rare but serious infection forming a pocket of pus around the kidney. Due to its potential for severe complications, including the spread of infection, prompt medical attention is crucial for individuals experiencing its symptoms.
What is a Perinephric Abscess?
A perinephric abscess is a collection of pus within the perirenal space, the area immediately surrounding the kidney. This space is enclosed by a fibrous sheath known as Gerota’s fascia, separating it from other abdominal structures. This pus forms as a result of a bacterial infection. It is distinct from a kidney infection, known as pyelonephritis, which involves inflammation of the kidney itself. Unlike a renal abscess, which forms within the kidney tissue, a perinephric abscess lies outside the kidney capsule but within the protective confines of the perirenal fat and fascia.
Common Causes and Symptoms
Perinephric abscesses can arise from an ascending urinary tract infection (UTI) that spreads from the bladder to the kidney and then to the surrounding area. Kidney stones are a significant risk factor as they can obstruct urine flow, creating an environment conducive to bacterial growth. This obstruction also makes it difficult for antibiotics to eradicate bacteria. Other factors include prior kidney surgery or trauma to the abdominal area.
Infections can also spread to the perirenal space through the bloodstream from distant sites, such as skin infections or endocarditis. Common bacteria include gram-negative bacteria like Escherichia coli and Proteus species, which often result from a ruptured renal abscess. Staphylococcus species can also cause perinephric abscesses, particularly in individuals with intravenous drug abuse, valvular heart disease, or those undergoing dialysis.
Symptoms of a perinephric abscess develop slowly and can be non-specific, often appearing over more than a week. Patients experience fever, chills, and pain in the flank, the side or back near the kidney. Other symptoms include abdominal pain, nausea, vomiting, night sweats, unexplained weight loss, and general fatigue or malaise.
How Doctors Diagnose Perinephric Abscess
Diagnosing a perinephric abscess begins with a review of the patient’s medical history and a physical examination. During the examination, a healthcare provider may find tenderness, pain, or swelling in the area around the kidney. The slow onset and non-specific nature of symptoms can make diagnosis challenging.
Blood tests include a complete blood count, which may show an elevated white blood cell count, indicating an infection. Inflammatory markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are elevated and monitored to assess treatment response. Urinalysis and urine culture are also conducted, although urine culture may only identify the responsible bacteria in about 30% of cases, and urinalysis can be normal if the abscess does not communicate with the urinary collecting system.
Imaging studies are crucial for confirming the diagnosis, with computed tomography (CT) scans with contrast being the preferred method. A CT scan reveals the size, location, and extent of the abscess, appearing as a hypodense area with a ring-like enhancement after contrast administration. Ultrasound can also indicate a perirenal hypoechoic area, sometimes with air inclusions.
Treatment Options
Treatment for a perinephric abscess involves a combination of antibiotics and drainage of the pus. Broad-spectrum antibiotics are administered intravenously to combat the infection. The antibiotic regimen is adjusted once culture results from the drained pus are available, allowing for targeted therapy against the identified bacteria.
Abscess drainage is a key step in treatment. Percutaneous drainage is a minimally invasive procedure where a needle and catheter are guided by imaging, such as ultrasound or CT, directly into the abscess to drain the pus. This method is favored due to its less invasive nature and faster recovery time. Abscesses larger than 3 cm in diameter typically require drainage.
For larger or more complex abscesses, or if percutaneous drainage is unsuccessful, surgical drainage may be necessary. This involves an open surgical procedure to drain the pus. In rare instances, if the kidney is severely infected or non-functional, a nephrectomy, which is the surgical removal of the kidney, might be considered. Addressing any underlying causes, such as kidney stones, is also important to prevent recurrence.
Recovery and Prognosis
Recovery from a perinephric abscess takes several weeks, with duration influenced by the infection’s extent and the patient’s response to therapy. Patients continue to receive antibiotic therapy, often transitioning from intravenous to oral antibiotics as their condition improves. Monitoring for symptom and infection resolution is maintained, and follow-up imaging ensures the abscess has fully resolved.
With timely and appropriate treatment, the prognosis for a perinephric abscess is favorable. However, delays in diagnosis or treatment can lead to serious complications, including the spread of infection throughout the body, a condition known as sepsis, or even kidney damage. If the infection is not cleared, it can lead to kidney failure or become deadly. To prevent recurrence, addressing underlying risk factors, such as managing diabetes or treating kidney stones, is important.