517

CT and Sonography ofSevere Renal and PerirenalInfections

William Hoddick1R. Brooke Jeffrey12

Henry I. Goldberg1Michael P. Federle12

Faye C. Laing12

Received August 18, 1 982: accepted October19, 1982.

Department of Radiology, University of Califor-nia, San Francisco, CA 94143.

2Department of Radiology, San Francisco Gen-eral Hospital, 1001 Potrero Ave., San Francisco,CA 94110. Address reprintrequests to R. B. Jef-frey.AJR 140:517-520, March 19830361 -8o3x/83/1 403-0517 $00.00 American Roentgen Ray Society

Twelve patients with urosepsis and severe renal or perirenal infections were evalu-ated with both computed tomography (CT) and sonography. Six patients had nineproven renal or perirenal abscesses larger than 2 cm in diameter. One patient hadmultiple microabscesses smaller than 1 cm. Five patients had CT or sonographicevidence of focal or multifocal bacterial nephritis. Computed tomography correctlydiagnosed all renal (six) and perirenal (three) abscesses. Sonography was falselynegative in a patient with multiple microabscesses and in another patient with a gas-forming perinephric abscess. In one patient with four bilateral renal abscesses, son-ography correctly diagnosed only one of the abscesses. In the five patients with focalor multifocal bacterial nephritis, CT demonstrated poorly defined, poorly enhancinglesions in all cases. Sonography was normal in three of these patients. Although thisreport is based on a limited experience, computed tomography seems to be the moresensitive method of evaluating severe renal and perirenal infections.

Acute pyelonephnitis in most adult patients will resolve promptly after appro-pniate antibiotic therapy. In patients unresponsive to initial medical management,radiologic investigation is warranted to exclude either ureteral obstruction or arenal abscess. Until recently excretory urognaphy and angiography have beenthe primary methods used in evaluating patients with suspected renal abscesses.Most patients with uncomplicated acute pyelonephnitis will have normal excretoryurograms [1 ]. In patients with abnormal urograms, such as a renal mass, com-puted tomography (CT) and sonography have largely supplanted angiognaphy asthe next imaging method of choice. Several reports have documented theusefulness of CT and sonography in evaluating both renal and penirenal infections[2-7]; however, there have been few direct comparisons between the two imagingmethods in patients with possible renal abscesses. We report the CT andsonographic findings in 1 2 such patients and review the noninvasive imaging ofrenal infections.

Subjects and MethodsDuring the period between January 1 979 and March 1 982, 1 2 patients were evaluated

with both CT and sonography for possible renal abscesses. Eleven of the 1 2 patients hada similar clinical presentation with an initial diagnosis of acute pyelonephnitis (fever, flankpain, and documented urinary tract infection) and a poor response to appropriate antibiotictherapy. One patient developed systemic candidiasis after chemotherapy for acute leuke-mia. The age range of the patients was 1 0-73 years (mean, 47 years). Five of the 12patients were diabetic.

Both the CT and sonographic examinations were performed within a 48-hr period. Inmost cases sonography was performed initially and the results were known before CT.Only three patients had excretory urography before CT and sonography. Sonography wasperformed with a commercially available digital gray-scale scanner using a 3.5 MHztransducer. Real-time examination was performed in all patients using a 3.5 MHz trans-

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518 HODDICK ET AU. AJR:140, March 1983

Fig. 1 -Diabetic with four staphytococcal renal abscesses. A, Left lowerpole renal abscess with perinephric extension and thickened renal fascia(arrow). B. Sonogram of left renal abscess. Poorly defined hypoechoic mass

ducer. CT was performed using a G.E. CT/T 8800 after intravenousurographic contrast material. Contiguous scans were performed at1 cm intervals through the kidneys.

The diagnosis of a renal or perirenal abscess was confirmed bysurgery (six patients) or diagnostic percutaneous needle aspiration(one patient). In the other five patients, CT and sonography dem-onstrated focal (two) or multifocal (three) bacterial nephritis. Noneof this group of patients required surgery and there was gradualclinical improvement after prolonged antibiotic therapy.

Results

Rena! Abscesses

Three patients had six proven renal abscesses larger than2 cm (fig. 1 ). A fourth patient with systemic candidiasis hadmultiple bilateral abscesses smaller than 1 cm (fig. 2).Bilateral staphylococcal abscesses were also noted in adiabetic with the smallest abscess about 2 cm. CT correctlydiagnosed all the renal abscesses in this series. With CT,the renal abscesses characteristically appeared as welldefined, low-density parenchymal lesions. Thickening ofadjacent renal fascia was noted in three of the abscesseswhich were contiguous with peninenal fat. In two abscesses

(arrows) without acoustic enhancement. C and 0, Multiple right renal ab-scesses (arrows) and E, left renal abscess (arrow) diagnosed by CT but notseen with sonography.

Fig. 2.-Multiple small renal abscesses from systemic candidiasis (blackarrows). Multiple hepatic abscesses (white arrow). Sonography failed todemonstrate renal lesions.

confined to the cortex and not adjacent to peninenal fat,there was no fascial thickening (fig. 1 D).

Sonography correctly diagnosed renal abscesses in two

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Fig. 4.-Diabetic with perirenal abscess diagnosed correctly by both CTand sonography. Perirenal fat obliterated by soft-tissue mass containing low-density abscesses (arrows). Proven Candida albicans perirenal abscess atsurgery.

AJR:140, March 1983 RENAL AND PERIRENAL INFECTIONS 519

Fig. 3.-A. Gas-forming renal andperirenal abscesses. CT also demon-strates focal bacterial nephritis (arrow).Slight enlargement of left psoas muscleadjacent to abscess. B, Sonogram ini-tially interpreted as showing no abscess.Reverberation from gas (arrows) notedin retrospect. Focal area of bacterial ne-phritis seen with CT not identified.

of three patients. The abscesses appeared as either acomplex fluid collection on hypoechoic mass with poorthrough transmission. In the patient with systemic candidi-asis, sonognaphy was normal. A false-negative diagnosisoccurred in another patient with a large abscess in the lowerpole of the left kidney (figs. 1 A-i D) in whom sonognaphyfailed to demonstrate three other smaller abscesses.

Perinephric Abscess

CT correctly diagnosed all three patients with surgicallyproven peninephnic abscesses (figs. 3 and 4). The CT find-ings included peninenal fluid collections (two patients) on gasbubbles (one patient) with distortion of the renal contourand thickening of adjacent renal fascia. Sonognaphy diag-nosed two of the three peninephnic abscesses, but wasfalsely negative in a patient with a gas-forming peninenalabscess.

Focal or Mu!tifoca! Bacteria! Nephritis

Five patients were included in this category. All patientsexhibited single (two patients) on multiple (three patients)

poorly defined areas of decreased contrast enhancementon CT (fig. 5). Sonography was abnormal in only two of thefive patients demonstrating a focal, hypoechoic, solid mass.In one of these patients, CT showed multiple areas ofinvolvement. Clinical follow-up in the five patients of 6-14months demonstrated resolution of the inflammatory proc-ess on antibiotic therapy. In two patients, follow-up CTshowed interval improvement at 4 and 6 weeks. There wasa correlation between multiple foci of involvement on CTand a protracted clinical course with more gradual clinicalimprovement.

Discussion

The diagnosis of renal and penirenal abscesses continuesto challenge clinicians and radiologists alike. Severe renalinfections may be viewed as a pathologic continuum, asinadequately treated interstitial infections may liquefy andevolve into an acute abscess. Although patients with bac-tenial nephnitis gradually improve with antibiotics, renal orpeninenal abscesses generally do not respond to antibiotictherapy alone. Therefore, it is of considerable clinical im-portance to distinguish interstitial infection from an abscessbecause of the potential need for surgical intervention.

In describing the CT appearance of renal abscesses,Rauschkolb et al. [2] noted that renal abscesses appear aswell defined, rounded areas without significant contrastenhancement. Unlike bacterial nephnitis, abscesses do nothave a loban distribution. Also strongly suggestive was ad-jacent peninephnic extension with thickening of the renalfascia. This finding was not present in two abscesses in ourseries confined to the cortex and not contiguous with pen-renal fat. One of the most consistent CT features among ourpatients was the sharp demarcation of abscesses fromadjacent enhancing renal panenchyma as opposed to thepoorly defined areas of focal bacterial nephnitis.

In describing the gray-scale sonographic features of renalabscesses, Wicks et al. [1 ] noted that renal abscessesgenerally must be at least 2-3 cm in diameter in order to bedetected by sonography. This is in keeping with our expe-nience, as the abscesses missed by sonognaphy in ourseries were all 2 cm on smaller. In addition to size limitations,

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520 HODDICK ET AL. AJR:140, March 1983

Fig. 5.-Multifocal bacterial nephri-tis. A, Enlarged right kidney with threepoorly defined areas of decreased en-hancement (arrowheads). B, Sonogramunderestimates extent of involvement asonly single hypoechoic area identified(arrows).

sonography cannot define fascial thickening on detect subtlealterations of peninephnic fat. Sonognaphy is useful in di-necting diagnostic needle aspiration of suspected ab-scesses, and an aggressive approach with percutaneousaspiration may overcome some of these limitations. Fluid-filled peninephnic abscesses may be readily diagnosed bysonography. The only peninephnic abscess missed in thisseries was a gas-containing abscess. In retrospect, pen-nephnic gas could be identified (fig. 3), but this was oven-looked on the initial examination.

Hoffman et al. [6] described the CT features in five diabeticpatients with acute pyelonephnitis. Excretory unognams inthree of these patients were normal. The authors concludedthat CT was more sensitive than excretory urography in thedetection of focal areas of interstitial infection. Lee et al. [7]described the CT and sonognaphic features of acute focalbacterial nephnitis in 1 3 patients. With sonography, areas offocal bacterial nephnitis appeared as hypoechoic solidmasses without definable walls. These corresponded topoorly defined, low-density areas on CT after intravenousadministration of contrast material. Rosenfield et al. [8]emphasized the lobar distribution of acute focal bacterialnephnitis that could be diagnosed via sonography. In ourseries of five patients with either focal or multifocal bacterialnephnitis, sonognaphy was negative in three patients inwhom CT showed clear-cut evidence of abnormal parenchy-mal enhancement. In one of the cases where sonographydemonstrated a single area of focal infection, CT showedthat sonography tended to underestimate the degree ofinvolvement, as multiple abnormal areas were identified.

The presence of multifocal bacterial nephnitis seemed tocorrelate well with increased clinical severity and the needfor prolonged antibiotic treatment.

In conclusion, although this is admittedly a small series ofpatients and further studies will need to corroborate thesefindings, it seems that CT is the more sensitive method fordiagnosis of both renal and penirenal infections.

REFERENCES

1 . Wicks JD, Thornbury JR. Acute renal infections in adults.Radio! Clin North Am 1 979; 1 2 :245-260

2. Rauschkolb EN, SandIer CM, Sumant P, Childs TU. Computedtomography of renal inflammatory disease. J Comput AssistTomogr 1 982;6 : 502-506

3, Edell SL, Bonavita JA. The sonographic appearance of acutepyelonephnitis. Radiology 1979;1 32 : 683-685

4. Gelman MU, Stone LB. Renal carbuncle: early diagnosis byretropenitoneal ultrasound. Urology 1976;6: 103-107

5, Schneider M, Becker JA, Stniano 5, Campos E. Sonographic-radiographic correlation of renal and perirenal infections. AJR1976;1 27: 1007-1 014

6. Hoffman EP, Mindelzun RE, Anderson RU. CT in acute pyelo-nephnitis associated with diabetes. Radiology 1 980; 1 35 : 691 -695

7. Lee KTL, McClennan BL, Melson GL, Stanley RJ. Acute focalbacterial nephnitis: emphasis on grey scale sonography andcomputed tomography. AJR 1 980;1 35 : 87-92

8. Rosenfield AT, Glickman MG, Taylor KJW, Crade M, HodsonJ. Acute focal bacterial nephritis (acute lobar nephronia). Ra-dio!ogy I 979;1 32 :553-561

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