Kidney Abscess - Types, Causes, Risk Factors, Symptoms and Treatment.

Introduction

A kidney abscess, also known as a renal abscess, is the circumscribed collection of pus in the renal parenchyma. They are believed to be caused as a result of the liquefaction phase of localized bacterial nephritis or hematogenous spread of infection from another site. It results from infection of the kidney by different bacterial species due to a variety of reasons. Most cases of renal abscess are reported to be caused as a result of urinary tract infections. Kidney abscess accounts for 0.2 % of all abdominal abscesses.

What Is Kidney Abscess?

A kidney abscess can be defined as the localized collection of pus in any part of the renal tissues leading to the spread of infection and other complications. It may appear as a complex lesion or intrarenal fluid collection layered by the inflammatory cells.

Based on the anatomic location of the abscess in the kidney, it can be categorized into three types,

• Perinephric Abscess - A perinephric abscess is a collection of pus in the perinephric fat (layer of fat surrounding the kidneys) and fascia surrounding the kidney.

• Renal Cortical Abscess - It is a term to describe the collection of pus in the renal cortex.

• Corticomedullary Abscess - A corticomedullary abscess is a collection of pus in the space joining the renal medulla and cortex.

Studies report that kidney abscesses resulting from focal infection usually result in abscesses in the medulla, whereas the hematogenous spread from a remote site will result in a cortical abscess. Either type can crack into the perinephric space causing a perinephric abscess.

What Are the Causes of Kidney Abscess?

The main cause of kidney abscesses is urinary tract infection (UTI). Other causes include:

• Kidney Stones - Kidney stones means formation of stones in the Kidney.

• Nephritis - Inflammation of the kidney.

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• Urinary Tract Surgery - Any surgery along the path of the urinary tract.

• Polycystic Kidney Disease - Formation of multiple cysts in the kidneys as a result of genetic inheritance.

• Vesicular Ureteral Reflux - This is the backflow of urine from the bladder into the ureter or the kidneys.

What Are the Risk Factors for Kidney Abscesses?

• Diabetes Mellitus - Patients with Increased and uncontrolled blood sugar levels are at increased risk of kidney abscess as the bacterias proliferate in the environment rich in glucose.

• Traumatized Kidney - Any type of injury to the kidneys would result in a kidney abscess.

• Skin Abscesses - Any pus collection in the skin can metastasize to the kidneys.

• Pregnancy - Pregnancy can also be a risk factor as urinary tract infections are more common in pregnancy.

• Intravenous Drug Abuse - As chances of infection are more in these patients.

• Immunocompromised State - Immunocompromised patients are at high risk due to the lack of immunity against pathogens.

What Is the Pathogenesis of Kidney Abscess?

Renal abscesses arise as a result of preexisting kidney disease or due to the hematogenous spread of infection from a distant site. Infection in the kidney is mainly caused by organisms such as Escherichia coli, Proteus, and Pseudomonas species, whereas the infection from a distant site is most commonly caused by Staphylococcus aureus. Infection by these organisms either from the local or distant site will lead to the formation of abscess, which is characterized by the intrarenal accumulation of fluid composed of dead cells and bacterial material in the center surrounded by collagenous tissue.

What Are the Symptoms of Renal Abscess?

• Pain during urination.

• Pyuria (presence of pus in the urine).

• Hematuria (blood in the urine).

• Weight loss.

• Night sweats.

• Abdominal pain.

• Fever and chills.

• Back pain.

How to Diagnose Renal Abscess?

Diagnostic tests include:

• Complete Blood Count - This will reveal the increased number of white blood cells (leukocytosis).

• Erythrocyte Sedimentation Rate (ESR) and C-reactive Protein (CRP) - Values are elevated, indicating active infection.

• Blood Culture - Reveal the growth of organisms in the blood.

• Gram Staining - Done to understand whether the organism causing the infection is gram-positive or negative.

• Urine Test - Reveals the presence of causative bacteria and pus in the urine.

• X-ray - This is the least advisable, as small abscesses are hard to appreciate in X-ray.

• Kidney Ultrasound - Kidney ultrasound helps visualize the abscess.

• Computerized Tomography (CT scan) - CT scan is the most preferred method to diagnose kidney abscesses.

What Are the Complications of Renal Abscesses?

Renal abscesses, if left untreated or unnoticed, may lead to the dissemination of the organisms throughout the body, causing a life-threatening condition called sepsis.

What Is the Prognosis of Renal Abscess?

Renal abscesses show a good prognosis with early recognition of the condition and treatment with appropriate antibiotics. The prognosis is reported to be bad when it progresses to sepsis.

What Is the Treatment for Renal Abscesses?

The various methods in the management of renal abscess involve:

Incision and Drainage

Once the kidney abscess is diagnosed, it is important to clear the infection by draining the pus through incision and drainage. Drainage of pus results in decreased bacterial load and increased renal perfusion, and the antibiotics can be delivered effectively. Incision and drainage in case of larger abscess need surgical intervention where a catheter is placed surgically to drain the abscess.

Percutaneous Drainage

It is a less invasive procedure in which the catheter is placed in the kidney with the aid of imaging guidance. With the CT or ultrasound guidance, the catheter is inserted into the skin over the kidney, and the pus is drained. The advantages of this technique include decreased morbidity by offering faster recovery than the open surgical technique, preserving the kidney by avoiding unnecessary damage to the kidney tissues, and the procedure can be performed under the local anesthetic.

Antibiotics

Antibiotics should be given based on the causative agents, appropriate choice of antibiotics is mandatory in the treatment of this condition. Studies have shown that around 75 % of kidney abscesses are caused by gram-negative bacteria, Escherichia coli (E-coli) being the most common organism; hence antibiotics should be chosen based on the culture reports. Intravenous (IV) administration of antibiotics is found to be more effective in managing it well.

Treating the Underlying Cause

The underlying cause for the formation of the renal abscess should be treated to prevent the recurrence of the condition. If kidney stones are present, they should be removed to avoid obstruction and reinfection of renal tissues.

Conclusion

A kidney abscess is an infectious condition where the pus accumulates in the renal tissue. With timely diagnosis and prompt treatment, the prognosis of this condition is good. Percutaneous nephrostomy and appropriate antibiotics are found to be the most effective in the management of kidney abscesses. The underlying conditions which serve as a secondary cause of kidney abscess should be addressed and should be eliminated to prevent reinfection or recurrence.