What is Perinephric Abscess?
A perinephric abscess is a pocket of pus that forms around the kidney, due to the breakdown of fatty tissue surrounding the kidney, often as a result of a urinary infection. In the past, most of these abscesses came from prolonged bloodstream infections with a bacteria called Staphylococcus aureus, which then spread to the kidney area. This was before the widespread use of antibiotics.
Nowadays, more than 75% of these abscesses are caused by complications arising from urinary tract infections. A perinephric abscess spreads more widely and affects the outer layer of the kidney (the renal capsule) and Gerota’s fascia, which is a layer of connective tissue around the kidney.
The pus from these abscesses can also spread from the Gerota’s fascia into the psoas and transversalis muscles—these are muscles in your lower back—and into the abdomen and pelvic area.
What Causes Perinephric Abscess?
A perinephric abscess is a pocket of pus that forms around the kidney. This can happen in a couple of ways. One way is if an infection spreads into the kidney from the bloodstream. Another way is if an infection in the urinary system, like the bladder, travels upwards to the kidney. In this situation, the infection usually also affects part of the kidney, called the renal pelvis.
Sometimes, the infection can spread out from the kidney into the fat surrounding it, creating the abscess. If a kidney abscess bursts, it can spread to the outer layer of the kidney and cause another kind of abscess. This often happens when the cause of the infection is a bacteria called staphylococcus.
Perinephric abscesses can also happen if an infection spreads from nearby organs or tissues, such as the liver, cervix, pancreas, gallbladder, or appendix. Other potential origins of the infection could be from physical injury, a disease affecting the small intestine called Crohn’s disease, or an infection in the spinal bones, known as vertebral osteomyelitis.
A bacteria called Staphylococcus aureus can cause an infection to spread to the perinephric fat via the bloodstream, usually leaving the kidney unaffected.
Often, the infections that cause perinephric abscesses are from a group of bacteria called gram-negative enteric bacilli, or a combination of different bacteria. The three most common bacteria found in these abscesses are Escherichia coli, Staphylococcus aureus, and Klebsiella pneumoniae.
Escherichia coli causes over half of perinephric abscesses. Infections from Staphylococcus aureus often happen through the spreading of the bacteria via the bloodstream.
Risk Factors and Frequency for Perinephric Abscess
People with certain health conditions are more likely to develop perinephric abscesses, which are pockets of pus around the kidneys. These health conditions include diabetes, pregnancy, urinary tract infections, and changes in the structure of the urinary tract. Such changes can include having kidney stones, especially large ones, having a neurogenic bladder, backflow of urine from the bladder to the kidney, growth of an obstructive tumor, cell death in the papilla of the kidney, and polycystic kidney disease. It’s also noteworthy that between 20% to 60% of people with perinephric abscesses also have kidney stones.
- Perinephric abscesses is more common in people with certain health conditions.
- These conditions include diabetes, pregnancy, and urinary tract infections.
- Structural abnormalities in the urinary tract can also make a person prone to perinephric abscesses.
- These abnormalities include having kidney stones (especially large ones), neurogenic bladder, urine backflow from the bladder to the kidney, obstructive tumor growth, cell death in the papilla of the kidney, and polycystic kidney disease.
- Of those with perinephric abscesses, 20% to 60% also have kidney stones.
Signs and Symptoms of Perinephric Abscess
A perinephric abscess is a condition usually linked with other health issues such as diabetes, pregnancy, urinary tract infection, and structural abnormalities in the urinary tract. These structural abnormalities can include issues like large staghorn stones, neurogenic bladder, vesicoureteral reflux, obstructive tumor, papillary necrosis, and polycystic kidney disease.
Typically, the symptoms of a perinephric abscess aren’t very specific and can take quite a while to develop. People tend to experience fever, flank pain, abdominal pain, and fatigue. The pain might also spread to the groin or leg if the infection expands. Although urinary tract infections usually involve symptoms like painful urination and frequent urination, these are not often seen in many patients with perinephric abscesses. They might also show symptoms such as appetite loss and painful urination, though these symptoms appear less frequently.
In a Korean study, the most common symptoms were fever and chills, reported in 75% and 63% of people respectively. On average, symptoms appeared 12 days before hospital admission.
- Physiological condition like diabetes or pregnancy
- Urinary tract structural abnormalities
- Slow onset of fever
- Flank pain
- Abdominal pain
- Fatigue
- Possible groin or leg pain
- Fever and chills
- Abdominal pain
- Appetite loss
- Painful urination
Older adults or people with autonomic neuropathy (for example, people with diabetes or chronic alcoholism) may have less pronounced symptoms. They might feel pain in the right upper quadrant if the abscess extends into the liver or chest pain if it extends into the lung and causes a pus-filled cavity. Many times, patients can show tenderness to percussion of the costovertebral area and might even have a palpable mass on physical examination. In some cases, there might be visible changes to the skin due to inflammation from the abscess.
Testing for Perinephric Abscess
Missing a diagnosis of a perinephric abscess, which is a pocket of pus in the tissue around the kidney, can increase the risk of severe outcomes, especially if a patient continues to have a fever after 4 to 5 days of antibiotics for a kidney infection called pyelonephritis.
Typical blood tests and a complete blood count are used to check the kidney function and the level of white blood cells. The test of the urine, known as a urinalysis, is conducted to check for the presence of pus or protein in the urine which indicate infection. However, the urinalysis may not show abnormalities in a perinephric abscess as it might not be connected with the kidney urinary system. Similarly, if the abscess has formed because bacteria reached the area through the bloodstream, there might not be any changes observed in urinalysis. Blood cultures can help to identify the bacterial infection if it has spread throughout the bloodstream.
Leukocytosis or an increase in white blood cells is a non-specific sign of infection; also, those with diabetes may initially present with acidosis, a chemical imbalance in the body. Signs of inflammation such as an increased erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are always seen in people with a perinephric abscess. These signs can also help to assess how well the treatment is working.
Imaging techniques can detect abnormalities related to a perinephric abscess. CT scans with a contrast dye are the preferred method. They can help to identify the abscess and how far it has spread. Other types of scans such as plain radiography or X-rays can suggest a perinephric abscess is present by identifying features such as a lack of clear margin between muscle and organs, presence of a mass or enlarged kidney, or a kidney with unclear borders.
Ultrasound scans can suggest an abscess if they show a separation between the lower density urine and higher density pus. An enhanced CT scan can help to identify abscess presence and size, and if it has spread to nearby areas, such as the liver or diaphragm.
The abscess might spread to the muscle and tissues of the back and sides (psoas and flank muscles), form a pocket of pus below the diaphragm, or extend downward potentially causing a groin abscess. It’s less common but the abscess could break into the peritoneal cavity (the area that contains the abdominal organs) or the colon.
Once a perinephric abscess is found, it is crucial to check for the presence of kidney stones, particularly in people with a high urine pH level which can point towards a specific type of infection caused by a urea-splitting organism.
Nuclear imaging and MRI are not generally used for diagnosing a perinephric abscess as these methods have limited usefulness in this context.
Treatment Options for Perinephric Abscess
If you have a perinephric abscess, which is a pocket of pus around the kidney, there are several treatment options available. These generally include a combination of antibiotics and, if necessary, a procedure known as percutaneous drainage. In this procedure, a specialist uses a thin, needle-like tube to remove the pus from your kidney area. If these treatments aren’t effective, surgery may be required.
Antibiotics prescribed would aim to fight off the specific types of bacteria causing the infection. For instance, if the perinephric abscess is linked with a kidney infection (pyelonephritis), antibiotics will be chosen to combat Enterobacteriaceae bacteria. And if the abscess is caused by Staphylococcus bacteria, the antibiotics will target this bacteria.
In certain circumstances, if you’re in a stable condition, the doctor might delay the antibiotic treatment and focus on the percutaneous drainage. This immediate approach helps to identify the bacteria causing the infection. Generally, abscesses that measure larger than 3 cm will require drainage, while those smaller than 3 cm could initially be treated just with antibiotics. If, however, your symptoms linger and medical imaging shows no improvement after a few days of antibiotics, then percutaneous drainage would be necessary.
The duration of antibiotic treatment is typically around 2 to 3 weeks and can be adjusted depending on your rate of recovery and the abscess’s resolution. After the drainage catheter is removed, if the infection was due to Enterobacteriaceae, transition to oral antibiotics may be possible. But if the infection was caused by Staphylococcus bacteria, the treatment course will continue to be with intravenous antibiotics.
Usually, a urologist is consulted when the abscess has been caused by an anatomical abnormality such as kidney stones blocking the urinary passage, or certain diseases that cause the urine to flow back into the kidney, or when the abscess is too big to be treated by antibiotics and percutaneous drainage. In such cases, surgical drainage of the abscess or removal of the kidney (nephrectomy) might be required.
It’s key to monitor your progress during treatment. Some signs of recovery include fading flank pain, stabilizing temperature, and improving blood tests results, including white blood cell count, CRP, and ESR. If treatment is successful, all these indicators should improve. However, if symptoms and abnormalities continue, doctors will repeat medical imaging (ultrasounds or similar). Medical imaging may also be necessary if the percutaneous drainage isn’t working as expected, as well as before being discharged to assess the improvement of the abscess.
What else can Perinephric Abscess be?
There are several conditions that may seem similar to a perinephric abscess. These include:
- Acute pyelonephritis complicated by papillary necrosis, which is a serious infection with damage to the kidney’s structure
- Emphysematous pyelonephritis, an infection that causes gas to build up in the kidney
- Acute lobar nephronia without renal tissue necrosis, a type of kidney infection that doesn’t involve pussing
- Xanthogranulomatous pyelonephritis, a severe form of long-term kidney infection that causes major kidney damage
- Malakoplakia, an inflammatory disease usually affecting the bladder, but can also affect the kidneys
- Renal cell carcinoma, a type of kidney cancer.
A distinguishing feature of perinephric abscess from these conditions can be established using enhanced computed tomography (CT) imaging.
What to expect with Perinephric Abscess
A perinephric abscess, an infection around the kidney, can result in serious sickness. The intensity of the illness greatly relies on how far the infection has spread and any other health conditions the person might have. On average, according to a study conducted in Korea on 63 patients with kidney and perinephric abscesses, patients had to stay in the hospital for about 15.3 days.
Certain factors can influence the severity of the condition and the length of the hospital stay. These include being older in age, having diabetes, the size of the abscess, experiencing lethargy (a state of fatigue or lack of energy), and suffering from renal insufficiency (where the kidneys are not working as well as they should be).
Possible Complications When Diagnosed with Perinephric Abscess
Some potential complications that can occur after medical procedures include:
- Sepsis: a dangerous infection that can spread throughout the body
- Pneumonia: an infection that causes inflammation in one or both of the lungs
- Bleeding: uncontrolled blood loss post-procedure
- Fistula formation: an abnormal passageway that forms between the stomach, small bowel, or lung and another body part
- Subphrenic abscess: an infected pocket of pus that forms under the diaphragm
- Potential rupture into the peritoneum: a tear that allows contents to spill into the abdominal cavity
- Possible perforation through the diaphragm: a hole that develops in the muscle separating your chest and abdomen
- Empyema: a condition where pus builds up in the space between the lungs and the inner surface of the chest wall
