Renal Abscess

The term renal carbuncle is used by some radiologists; it has no specific imaging definition and some use it as a synonym for renal abscess. The term is probably best avoided in describing imaging findings. At times acute pyelonephritis progresses to scattered small abscesses, which eventually coalesce into a gross abscess. The involved kidney is often enlarged. An abscess tends to be sharply marginated and has a rim of contrast enhancement.
A subcapsular abscess displaces and compresses the adjacent renal parenchyma. Gas within an abscess is not common. Some renal abscesses are associated with extrarenal abscesses in adjacent structures. In general, CT detects renal and extrarenal abscesses better than US. Still, US detects the larger abscesses and often is more readily available in monitoring resolution. Ultrasonography of an abscess identifies a complex, thick-walled, cystic, fluid-containing mass. Abscesses tend to be hypoechoic or anechoic.
With maturity the abscess outline becomes better defined.
Gadolinium-enhanced MRI reveals renal abscesses as heterogeneous hypointense tumors; perinephric inflammatory stranding is common. The MRI findings are similar to those seen with contrast-enhanced CT, and in patients
who should not receive iodinated contrast, MRI is a viable alternative. An abnormal scintigram showing photopenic regions in the kidney is nonspecific and does not differentiate between inflammation and abscess. The imaging differential for most intrarenal abscesses includes a hemorrhagic or infected cyst and a cystic neoplasm.
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Radiology images of right renal abscess. Contrast-enhanced CT reveals a huge fluid-filled structure at the superior pole of the right kidney (arrows). It was drained percutaneously.
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