What is the evidence for renal ultrasound in acute pyelonephritis (infection of the kidney)

From the Guidelines

Renal ultrasound should be performed to rule out urinary tract obstruction or renal stone disease in patients with a history of urolithiasis, renal function disturbances, or a high urine pH, as recommended by the European Association of Urology guidelines 1. This approach is crucial in identifying potential complicating factors that may affect treatment outcomes. The use of renal ultrasound in these specific scenarios can help identify complications such as abscess formation, obstruction, or structural abnormalities that may require intervention beyond antibiotics.

In general, renal ultrasound is not routinely recommended for uncomplicated pyelonephritis in adults 1. However, it may be considered in certain clinical scenarios, such as:

• Patients with persistent fever beyond 72 hours of appropriate antibiotic therapy
• Recurrent pyelonephritis
• Suspected urinary obstruction
• History of urolithiasis
• Immunocompromised status
• Abnormal renal function

The rationale for selective use of renal ultrasound in adults is that most cases of uncomplicated pyelonephritis resolve with appropriate antibiotic therapy alone, and routine imaging does not change management or outcomes 1. When indicated, renal ultrasound can provide adequate initial assessment and identify potential complications that may require further intervention. If ultrasound findings are concerning or inconclusive, further imaging with CT scan may be warranted 1.

It is essential to note that patients with severe sepsis, shock, or those who fail to respond to appropriate therapy should undergo prompt imaging to rule out complications requiring urgent intervention 1. In children, renal ultrasound is more commonly indicated to evaluate for anatomic abnormalities that might predispose to infection 1.

From the Research

Renal Ultrasound in Pyelonephritis

• The use of renal ultrasound in adult acute pyelonephritis is evaluated in several studies 2, 3, 4.
• A review of 463 patients diagnosed with acute pyelonephritis found that renal ultrasound changed the initial diagnosis to complicated pyelonephritis in only 11.5% of cases 2.
• The study suggests that renal ultrasound is not necessary for every patient with acute pyelonephritis, but may be useful in patients with persistent fever, urinary tract anomalies, renal lithiasis, pregnancy, atypical clinical presentation, or diabetes mellitus 2.
• Contrast-enhanced ultrasound (CEUS) is a valuable tool in the diagnosis and follow-up of acute pyelonephritis, aiding in distinguishing small simple nephritic involvement from abscess complications and monitoring their evolution over time during antibiotic therapy 3.

Indications for Renal Ultrasound

• Renal ultrasound may be indicated in patients with:
  • Persistent fever longer than 72 hours 2
  • Antecedents of anomalies of the urinary tract 2
  • Antecedents of renal lithiasis 2
  • Pregnancy 2, 4
  • Atypical clinical presentation 2
  • Diabetes mellitus 2
• Ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) can contribute to more efficacious treatment of patients at different stages of acute pyelonephritis 4.

Diagnostic Findings

• The main ultrasound signs of acute pyelonephritis include:
  • Decreased mobility of the kidney 4
  • Enlargement of the kidney 4
  • Thickened parenchyma 4
  • Hydrophilic parenchyma 4
  • Impairment of corticomedullary differentiation 4
• The typical CT signs of acute pyelonephritis include:
  • Enlargement of the kidney with thickened parenchyma 4
  • Impairment of corticomedullary differentiation 4
• The main MRI signs of acute pyelonephritis include:
  • Enlargement of the kidney (>12 cm lengthwise) 4
  • Thickened parenchyma (<2 cm in the median segment of the kidney) 4
  • Impairment of corticomedullary differentiation 4