Pyonephrosis (Pus Collection in the Kidney)

What is pyonephrosis?

Pyonephrosis is a condition where pus collects in the kidney as result of an infection with a urinary tract obstruction. A kidney infection, known as pyelonephritis, is mainly bacterial in origin. If the pus cannot drain out of the kidney due to some obstruction in the ureter usually, it accumulated within the collecting system of the kidney and can lead to the formation of an abscess. Pyoneophrosis is a very serious condition because the pus is under pressure and can therefore lead to a rapid spread of the infection possibly leading to sepsis. This is life-threatening. Pyonephrosis is a very rare condition, both in children and adults. Although it is difficult to estimate how common the condition may be, patients with blockages of the urinary tract are at a greater risk and in particular patients with a compromised immune system.

Why does pus collect in the kidney?

Urine is produced in the kidney by filtering of fluid from the blood in the functional unit of the kidney, the nephron. Substances that need to be conserved are reabsorbed in the tubules and unwanted substances and wastes are passed out with the urine. There are about 1 million nephrons functioning in this manner and passing out the urine into the collecting channels in the kidney which eventually drain into the renal pelvis. From here the urine passes from the renal pelvis into the ureter and empties into the bladder where it is stored until voiding.

Pyelonephritis (kidney infection) is due to bacteria. The bacteria may reach the kidney through the bloodstream (hemtogenous spread) or from an infection that originates lower down the tract (ascending infection). Naturally pus in the kidney will drain out with the urine (pyruria) unless it is walled off in an abscess. In pyonephrosis, the situation is not just about an abscess in the kidney. Instead the passage of urine is blocked due to some obstruction in the urinary tract, like a urinary stone, and therefore the urine and pus collects in the kidney.

Accumulation of urine and pus in the renal pelvis leads to hydronephrosis. Collection of pus within the renal pelvis may lead to an abscess formation. This worsens the outlook of the condition as an abscess is a walled off collection of pus. The body’s immune defenses can therefore not reach the site and act against the invading microbes. In addition, antibiotics may not be able to eradicate the bacteria protected within the abscess. It is possibly for the hydronephrotic kidney to rupture, empty the contents into the peritoneal cavity and allowing for dissemination of the infection.

Signs and Symptoms

Pyonephrosis is essentially a combination of urinary tract obstruction and kidney infection (pyelonephritis) and the symptoms would be indicative of these conditions. In fact pyonephrosis does not usually present with specific symptoms and it should be suspected as a possible consequence in these conditions. Similarly, the complications of pyonephrosis may also contribute to the clinical presentation. Some of the symptoms that should raise the concern about pyonephrosis includes :

  • Flank pain, although the patient may report back pain and groin pain.
  • Fever which may be fluctuating or worsening.
  • Nausea and vomiting.
  • Little or no urine (anuria).
  • Weak and narrow urine stream.

The symptoms of peritonitis may also be present and abdominal pain, tenderness, abdominal distension, diarrhea or constipation with the inability to pass gas may also be present. Sepsis is common in severe untreated cases, especially in immunocompomised patients. Apart from the other symptoms mentioned above, there may also be rapid heart rate and a rapid breathing rate in sepsis. When the mental status is altered and the blood pressure is very low, severe sepsis or septic shock has arisen and death is a very likely consequence.

Causes of Pyonephrosis

Since there is urinary tract obstruction along with a kidney infection, is it important to consider the cause of each of these conditions.

The infection is mainly due to bacteria and the most common species is Escherichia coli (E.coli), usually from the rectum and feces. Less commonly, Candida species of yeasts and other fungi may also cause an infection. It is also important to note that a fungal infection is also a predisposing factor in pyonephrosis when fungal balls cause an obstruction of the urinary tract. This is more likely to occur in a person with a weakened immune system, like in HIV/AIDS, and people who have used antibiotics over a prolonged periods.

Other bacteria that may cause pyonephrosis includes Enterococcus, Enterobacter, Klebsiella, Proteus, Pseudomonas, Bacteroides, Staphylococcus and Salmonella species. Methicillin-resistant Staphylococcus aureus (MRSA) may also cause pyonephrosis and is often difficult to treat. A less common infectious cause is Mycobacterium tuberculosis, the organism responsible for tuberculosis (TB). M. tuberculosis can cause both an infection and narrowing of the ureter (stricture).

There are a number of different reasons for urinary tract obstruction. In most cases it is urinary stones that are responsible for the obstruction but various other physical blockages may be responsible. This includes pregnancy, cancer, fungus balls, ureterocele, ureteral strictures, tuberculosis and neurogenic bladder. Sometimes a complicated infection can lead to the obstruction and thereby progress to pyonephrosis. At other times an obstruction even without an infection increases the chance of a subsequent urinary tract and kidney infection.

Tests and Diagnosis

Pyonephrosis can lead to kidney failure and sepsis. Therefore it is important that initial tests also evaluate for the possibility of these conditions. Blood and urine tests are the main investigations to diagnose pyonephritis along with the clinical presentation and the patient’s medical history. When urine cannot be collected due to the obstruction, a sample has to be removed from the collecting system of the kidney. Imaging studies like an ultrasound, CT scan and MRI in particular are useful for identifying the obstruction and changes in the kidney associated with pyonephritis.

  • Blood tests :
    – Complete blood count (CBC)
    – Blood urea nitrogen (BUN) and creatinine
    – Blood culture
  • Urine tests :
    – Urinalysis
    – Urine culture

Pyonephrosis Treatment

The main approach to treating pyonephritis is the administration of intravenous (IV) antibiotics like gentamicin, ampicillin and sometimes clindamycin as well. Surgical intervention is often necessary and is aimed at draining the urine and pus from the kidney. This can be accomplished by one of two ways depending on the status of the patient.

  • Placement of a ureteral stent to widen the ureter thereby allowing the urine and pus to exit the kidney through the urinary tract. This is known as retrograde decompression. Refer to the video below of ureteral stenting.
  • Placement of a tube through the skin into the renal pelvis to allow the urine and pus to drain out directly into the exterior through a nephrostomy tube. This is known as antegrade decompression.

In rare instances, the kidney may be removed thereafter. However, it is still debated as to whether a nephrectomy (surgical removal of the kidney) is necessary.Complications such as peritonitis and sepsis needs to be treated accordingly.

References :

http://www.biomedcentral.com/content/pdf/1754-9493-6-10.pdf

http://emedicine.medscape.com/article/440548-overview

http://kidney.niddk.nih.gov/kudiseases/pubs/pyelonephritis/