From the Guidelines
For suspected pyelonephritis or renal abscess, a single-phase CT with IV contrast is the preferred imaging choice. This is based on the most recent and highest quality study available, which suggests that contrast-enhanced CT can detect signs of pyelonephritis, including focal or multifocal decreased parenchymal enhancement, and complications such as renal or perirenal abscess or emphysematous pyelonephritis 1.
The use of IV contrast in CT imaging allows for better evaluation of the kidney, including renal perfusion and function, and provides superior anatomic detail and improved sensitivity for detecting underlying congenital or acquired renal abnormalities 2. A retrospective study of patients with suspected pyelonephritis who underwent both unenhanced and contrast-enhanced CT found that contrast-enhanced CT detected parenchymal involvement in 62.5% of patients, whereas unenhanced CT detected parenchymal involvement in only 1.4% of cases 1.
Some key points to consider when using CT with IV contrast for suspected pyelonephritis or renal abscess include:
- The contrast highlights areas of inflammation, showing decreased enhancement in affected areas of the kidney during pyelonephritis and rim enhancement around abscesses 1
- The contrast also helps evaluate the collecting system and surrounding structures 1
- A single-phase approach reduces radiation exposure and is more time-efficient compared to the dual-phase study 1
- If there are concerns about contrast-induced nephropathy or the patient has contraindications to contrast, alternative imaging such as ultrasound or non-contrast CT may be considered, though these are less sensitive for detecting early inflammatory changes 1
Overall, the use of a single-phase CT with IV contrast is the preferred imaging choice for suspected pyelonephritis or renal abscess, due to its high sensitivity and ability to detect complications and underlying renal abnormalities 1.
From the FDA Drug Label
Utilization of a continuous scanning technique (ie, dynamic CT scanning) may improve enhancement and diagnostic assessment of tumor and other lesions such as abscess, occasionally revealing unsuspected or more extensive disease For example, a cyst may be distinguished from a vascularized solid lesion when precontrast and enhanced scans are compared; the nonperfused mass shows unchanged x-ray absorption (CT number) A vascularized lesion is characterized by an increase in CT number in the few minutes after a bolus of intravascular contrast agent; it may be malignant, benign, or normal tissue, but would probably not be a cyst, hematoma, or other nonvascular lesion Because unenhanced scanning may provide adequate diagnostic information in the individual patient, the decision to employ contrast enhancement, which may be associated with risk and increased radiation exposure, should be based upon a careful evaluation of clinical, other radiological, and unenhanced CT findings.
The main difference between CT kidneys with and without contrast versus CT with IV contrast when looking for pyelonephritis or renal abscess is that:
- CT with contrast can help distinguish between a cyst and a vascularized solid lesion, such as an abscess, by showing an increase in CT number after contrast administration.
- CT without contrast may provide adequate diagnostic information, but contrast enhancement can improve the diagnostic assessment of lesions, including abscesses.
- The decision to use contrast enhancement should be based on a careful evaluation of clinical, radiological, and unenhanced CT findings, considering the potential risks and increased radiation exposure [3] [4]. Key points:
- Contrast enhancement can improve diagnostic assessment of lesions.
- CT without contrast may be sufficient in some cases.
- Decision to use contrast should be based on individual patient evaluation.
From the Research
CT Kidneys with and without Contrast
- CT scans with contrast are typically used to diagnose pyelonephritis and renal abscesses, as they provide better visualization of the kidneys and any potential abnormalities 5.
- However, in patients with renal failure, CT scans with contrast cannot be performed, and alternative imaging modalities such as diffusion-weighted MRI may be used instead 6.
- CT scans without contrast may be used in patients with renal failure or those who are allergic to contrast agents, but they may not provide as much detail as contrast-enhanced CT scans.
CT with IV Contrast
- CT scans with IV contrast are more sensitive than non-contrast CT scans for diagnosing pyelonephritis and renal abscesses 6.
- IV contrast helps to highlight any areas of inflammation or infection in the kidneys, making it easier to diagnose pyelonephritis and renal abscesses.
- However, CT scans with IV contrast may not be suitable for patients with renal failure or those who are allergic to contrast agents.
Comparison of Imaging Modalities
- Diffusion-weighted MRI has been shown to be highly sensitive and specific for diagnosing pyelonephritis and renal abscesses, especially in patients with renal failure or those who are allergic to contrast agents 6, 7.
- Ultrasound may be used as an initial imaging modality for patients with suspected pyelonephritis or renal abscesses, but it may not provide as much detail as CT or MRI scans 8.
- CT scans with IV contrast are generally considered the gold standard for diagnosing pyelonephritis and renal abscesses, but alternative imaging modalities such as MRI and ultrasound may be used in certain situations.
Key Findings
- The minimum apparent diffusion coefficient (ADC) values can be used to differentiate between renal abscesses and uncomplicated pyelonephritis 6, 7.
- CT scans are more useful for diagnosing renal calculi and emphysematous pyelonephritis than MRI or ultrasound 6.
- The use of imaging technologies such as ultrasound, CT, and MRI can contribute to more efficacious treatment of patients with pyelonephritis and renal abscesses 8.