Imaging Studies for Renal Abscesses due to Pyelonephritis

Modalities for Renal Abscess Imaging

• The American College of Radiology recommends computed tomography (CT) with contrast of the abdomen and pelvis as the imaging study of choice for detecting renal abscesses secondary to pyelonephritis, due to its high sensitivity and specificity for identifying parenchymal changes and collections 1, 2
• CT with contrast has a significantly higher detection rate of renal abscesses (4.0%) compared to ultrasound (1.1%) 2
• The nephrographic phase (90-100 seconds post-contrast) has an accuracy of 90-92% for the diagnosis of pyelonephritis and its complications 3
• CT with contrast significantly improves the detection of parenchymal changes, renal abscesses, and acute extrarenal conditions that may present clinically as suspected pyelonephritis 2, 4
• The American College of Radiology suggests that CT should include the pelvis to identify possible abnormalities such as distal ureteral or bladder stones, congenital anomalies, and other potential sources of pyelonephritis 2
• Ultrasound has significant limitations for detecting renal abscesses with a sensitivity significantly lower than CT 1, 2
• Ultrasound with color Doppler increases sensitivity for detecting pyelonephritis beyond grayscale ultrasound but remains inferior to CT 5, 4
• Ultrasound with contrast improves sensitivity for detecting complicated pyelonephritis and renal abscesses compared to non-contrast ultrasound 5, 4
• The American College of Radiology recommends magnetic resonance imaging (MRI) as a particularly useful alternative in patients for whom iodinated contrast should be avoided 7, 3
• Diffusion-weighted imaging (DWI) sequences offer a viable alternative when contrast cannot be administered 3, 8
• Renal abscesses show significantly lower apparent diffusion coefficient (ADC) values than areas of pyelonephritis 3
• A disadvantage of MRI compared to CT is its lower ability to detect small stones and gas in emphysematous pyelonephritis 3, 8

Algorithm for Selecting Imaging Studies

• For patients with suspected renal abscess due to pyelonephritis who do not respond to treatment, the American College of Radiology recommends CT with contrast of the abdomen and pelvis as the first-line study 1, 2
• For patients with contraindications to iodinated contrast, MRI with diffusion sequences is the preferred alternative 3, 8
• Ultrasound with color Doppler is a second option for patients with contraindications to iodinated contrast 5, 4
• For pregnant patients, ultrasound with color Doppler is recommended as the initial study 6
• If ultrasound is not conclusive, non-contrast MRI may be considered for pregnant patients 3, 6

Important Considerations

• CT is superior to other imaging modalities in investigating complications such as renal or perirenal abscesses 2, 4
• Image-guided percutaneous interventional procedures are safe and effective for controlling or curing infection in many patients 2, 4
• The inclusion of the pelvis in CT studies is crucial for detecting important abnormalities such as stones or congenital anomalies 2, 4