Perirenal Gas Producing Infection

The radiologic features of a perirenal space gas-producing infection are distinctive. Its recognition is related directly to an understanding of the characteristic appearance of the acutely distended cone of renal fascia and the preferential spread through the rich perirenal fat dorsal to the kidney.

The gas may encircle the kidney or present as a mottled collection of radiolucencies within the shadows of the perirenal fat. Figure 8—124 illustrates the typical distribution in a diabetic female. Three characteristic features localize the infection to the perirenal space:

Perirenal Space

Fig. 8—124. Acute gas-producing left perirenal abscess.

(a) In addition to the mottled gaseous radiolucencies, fluid distention of the renal fascial cone overlies the iliac crest, presenting a typical convex inferior border (arrows).

(b) Oblique view demonstrates the preponderance of gas and fluid in the perirenal fat dorsal to the kidney. Inflammatory thickening of the anterior renal fascia is shown as a striplike density (arrowheads). (Reproduced from Meyers.8)

Fig. 8—124. Acute gas-producing left perirenal abscess.

(a) In addition to the mottled gaseous radiolucencies, fluid distention of the renal fascial cone overlies the iliac crest, presenting a typical convex inferior border (arrows).

(b) Oblique view demonstrates the preponderance of gas and fluid in the perirenal fat dorsal to the kidney. Inflammatory thickening of the anterior renal fascia is shown as a striplike density (arrowheads). (Reproduced from Meyers.8)

1. Associated exudate distends the cone of renal fascia so that its lower border can be identified as an in-feriorly convex shadow overlying the iliac crest.

2. The gas is most prominent within the rich fat posterior to the kidney.

3. Inflammatory thickening of the renal fascia itself may be seen.

The inferiorly convex border of the distended peri-renal space is a highly reliable localizing sign (Fig. 8125). Figure 8-126a demonstrates this finding at an early stage in a diabetic patient with pyelonephritis and fever. Twenty-four hours later (Fig. 8-126b), a diffuse gas-producing infection of the perirenal space becomes ap parent. When localization occurs, it preferentially develops posterior to the kidney (Fig. 8-127).

Fulminating infection may disrupt the perirenal fas-cial boundaries, allowing the gas to escape to other compartments. Figure 8-128 demonstrates acute fascial violation with direct extension into the flank fat. The resulting decompression of the perirenal space may not distend it to the level of the iliac crest, but it tends to maintain a diagnostic silhouette with an inferiorly convex lower border.

Bilateral perirenal gas-producing infections are unusual but their contours are again distinctive (Fig. 8129). In such instances, septic emboli or retrograde pyelonephritis from the bladder should be particularly considered.

Fig. 8-125. Right perirenal gas-producing infection in a diabetic.

A convex lower border (arrows) at the level of the iliac crest characterizes the distended cone of renal fascia.

Where Iliac Crest Bladder

Fig. 8-126. Acute gas-producing perirenal infection.

(a) In addition to a few ill-defined mottled lucencies in the right flank, a crescentic gas collection (arrows) overlies the iliac crest.

(b) The next day, extensive infection developed throughout the perirenal space.

Fig. 8-126. Acute gas-producing perirenal infection.

(a) In addition to a few ill-defined mottled lucencies in the right flank, a crescentic gas collection (arrows) overlies the iliac crest.

(b) The next day, extensive infection developed throughout the perirenal space.

Fig. 8—127. Localized gas-producing perirenal infection.

The process has localized behind the kidney, displacing it anteriorly (lateral view, retrograde study).

Fig. 8—127. Localized gas-producing perirenal infection.

The process has localized behind the kidney, displacing it anteriorly (lateral view, retrograde study).

Fig. 8—128. Perirenal gas-producing infection.

The process has broken into and extends down the flank fat (arrows).

Fig. 8—129. Bilateral perirenal gas-producing infections.

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