Pyelonephritis is a severe infection affecting the kidneys and the renal pelvis, the funnel-shaped part of the kidney that collects urine. Ultrasound imaging is a common diagnostic tool used to evaluate and manage this kidney infection. This article explores the role of ultrasound in assessing pyelonephritis.
Understanding Pyelonephritis
Pyelonephritis is a type of urinary tract infection (UTI) that has ascended to the kidneys. The most common cause is the bacterium Escherichia coli (E. coli), which enters the urinary tract through the urethra. Symptoms include fever, chills, pain in the lower back or flank, nausea, vomiting, and painful or frequent urination.
If left untreated, pyelonephritis can lead to serious complications such as permanent kidney damage or the spread of infection into the bloodstream, known as sepsis. Children and individuals with weakened immune systems or urinary tract abnormalities face a higher risk. Prompt diagnosis and antibiotic treatment are important to manage the infection and prevent adverse outcomes.
Why Ultrasound is Used for Pyelonephritis
Ultrasound is frequently used for suspected pyelonephritis due to its advantages. It is a non-invasive imaging technique that does not use ionizing radiation, making it suitable for children and pregnant women. Its widespread availability and relatively lower cost compared to other imaging modalities also contribute to its use.
Ultrasound primarily helps identify complications associated with pyelonephritis, such as urinary tract obstruction. It can reveal kidney stones or other blockages that impede urine flow, leading to hydronephrosis (swelling of the kidney due to urine backup). Ultrasound can also detect collections of pus, known as abscesses, or fluid around the kidney, which may necessitate different treatment approaches.
What Pyelonephritis Ultrasound Reveals
While ultrasound may not directly visualize the infection in all cases of pyelonephritis, it is highly effective at identifying related complications and anatomical changes. One common finding is kidney enlargement or swelling, which can indicate inflammation within the organ. The sonographic appearance may also show changes in the kidney’s echogenicity, appearing as focal hypoechoic (darker) or hyperechoic (brighter) regions, reflecting areas of edema or inflammation.
The presence of hydronephrosis, characterized by dilated renal collecting systems, is a significant finding that suggests an obstruction preventing urine drainage from the kidney. Ultrasound can also clearly show kidney stones, which are a common cause of obstruction and can predispose individuals to kidney infections. In more severe cases, the ultrasound may reveal abscesses within the kidney or fluid collections surrounding it, known as perinephric fluid. A loss of the normal distinction between the kidney’s outer cortex and inner medulla can also be observed in acute pyelonephritis.
The Ultrasound Examination Process
Undergoing a kidney ultrasound for suspected pyelonephritis is a straightforward and painless procedure. Patients lie on an examination table, and a clear, water-soluble gel is applied to the skin over the abdomen and flank area. This gel helps the ultrasound transducer glide smoothly and ensures good contact.
The sonographer moves the transducer over the skin, capturing real-time images of the kidneys and surrounding structures. Patients might be asked to hold their breath briefly or change positions for clearer visualization. While a full bladder may sometimes be requested for better bladder imaging, it is not always a strict requirement for kidney scans. The entire procedure usually takes around 20 to 30 minutes, and patients can resume their normal activities immediately afterward.
Limitations and Complementary Imaging
Despite its benefits, ultrasound has limitations in diagnosing pyelonephritis. In early or mild cases, the kidney may appear normal on ultrasound, as it is less sensitive than other imaging modalities for detecting subtle changes in kidney tissue. It also has a lower sensitivity compared to computed tomography (CT) scans for identifying small abscesses or diffuse inflammation within the kidney parenchyma.
If ultrasound findings are inconclusive or if complications like a large abscess or gas-forming infection are strongly suspected, additional imaging may be necessary. Computed tomography (CT) scans are often considered the gold standard for providing more detailed anatomical information and a broader view of the abdominal cavity. Magnetic resonance imaging (MRI) may be used in specific situations, such as in pregnant women or patients who cannot receive CT contrast. Ultrasound frequently serves as an initial screening tool, with further imaging determined by clinical symptoms and initial findings.