Acute Focal Bacterial Nephritis: Focal Pyelonephritis that May Simulate Renal Abscess

0022-5347 /81/1265-0670$02.00/0 Vol. 126, November

THE JOURNAL OF UROLOGY

Printed in U.S.A.

Copyright© 1981 by The Williams & Wilkins Co.

Case Reports ACUTE FOCAL BACTERIAL NEPHRITIS: FOCAL PYELONEPHRITIS THAT MAY SIMULATE RENAL ABSCESS W. DAVID McDONOUGH, CARL M. SANDLER* AND GEORGE S. BENSON From the Departments of Diagnostic Radiology and Surgery, Division of Urology, The University of Texas Medical School at Houston, Houston, Texas

ABSTRACT

We report 4 cases of acute focal bacterial nephritis, a solid inflammatory lesion of the kidney. In each patient the findings on excretory urography, when combined with the clinical features, suggested the possibility of a renal abscess. Ultrasonography and computerized tomography aid in distinguishing this solid inflammatory process from that of frank abscess. The possible etiology of acute focal bacterial nephritis, its evolution to abscess formation and its distinguishing features are discussed. Abnormalities on excretory urography (IVP) in acute pyelonephritis may include focal or diffuse renal enlargement, diminished nephrographic density, delayed caliceal appearance time, faint visualization of the collecting system as well as pyelocaliectasis and ureterectasis. 1 Recently, attention has been directed to the focal swelling or mass present as the predominant radiographic abnormality in patients with clinical evidence of acute pyelonephritis. 2 The term acute focal bacterial nephritis or acute lobar nephronia has been given to describe such findings, which are defined as a renal mass caused by an acute focal infection without frank abscess formation. Herein we report on 4 patients with acute pyelonephritis who were found to have a renal mass on an IVP. Each case represents an example of acute focal bacterial nephritis. CASE REPORTS

Case 1. E. P., a 49-year-old woman, presented to the emergency room with a 12-hour history of severe right costovertebral angle pain radiating to the vulva, associated with urinary urgency and frequency as well as dysuria, chills and fever. Temperature was lOlF. Physical examination revealed right upper quadrant and right flank tenderness to percussion and palpation. The white blood count was 23,000 with a left shift and urinalysis showed 40 to 50 white blood cells per high power field and many bacteria. Urine culture yielded 105 colonies per cc of Escherichia coli. An IVP demonstrated bilaterally enlarged kidneys with prompt excretion of contrast material. A poorly defined intrarenal mass with diminished opacification was pres· ent along the upper lateral margin of the right kidney. In addition, a left renal calculus was present that had remained unchanged in position or configuration from an earlier study obtained 6 years previously. An abdominal computerized tomographic (CT) examination demonstrated a rounded area of decreased attenuation along the lateral aspect of the right kidney (fig. 1). Diagnosis was acute focal bacterial nephritis, and the patient was treated with parenteral antibiotics and intravenous fluids. Defervescence occurred within 3 days of hospitalization and shortly thereafter she became asymptomatic. The patient was maintained on antibiotics for a total of Accepted for publication January 23, 1981. * Requests for reprints: Department of Radiology, University of Texas Medical School, 6431 Fannin St., Houston, Texas 77030.

13 days. A followup IVP and repeat abdominal CT scan (fig. 2) 6 months later failed to reveal any evidence of a renal lesion. The patient has remained asymptomatic and urine cultures have been sterile. Case 2. A. H., a 49-year-old female diabetic, was hospitalized with the chief complaints of right flank pain, chills and fever. Temperature was 102F orally. Physical examination disclosed tenderness in the right upper quadrant and right flank. The white count was 18,000 with a left shift. Serum creatinine was 2.4 mg. per cent, while the serum glucose was 497 mg. per cent. Urinalysis demonstrated 10 to 15 white blood cells per high power field, many bacteria and 3+ glucosuria. Urine and blood cultures yielded 105 colonies per cc Enterobacteria aerogenes. An IVP revealed delayed visualization of the collecting system of the right kidney along with diminished filling of the corresponding lower pole calices (fig. 3, A). Focal bulbous enlargement of the lower pole of the right kidney suggested the presence of a mass. Diagnosis was acute pyelonephritis and uncontrolled diabetes mellitus. The patient was given gentamicin and insulin. Serum glucose was controlled and the glucosuria resolved. The patient became afebrile 5 days after hospitalization. A repeat IVP 10 days after hospitalization demonstrated a previously obscured lower pole calix and a decrease in the size of the lower pole mass (fig. 3, B). The patient received a 10-day course of parenteral antibiotics. An IVP 3 months later revealed 2 normal kidneys with prompt excretion and no evidence of the previous right lower pole mass (fig. 4). Case 3. P. C., a 27-year-old white woman, was admitted initially elsewhere with a 7-day history of dysuria and frequency. Temperature was 101.8F orally and physical examination elicited tenderness along the right flank. The white blood count was 18,000, while urinalysis revealed 8 to 10 white blood cells per high power field. A urine culture obtained after the patient had been started on antibiotics was sterile. An IVP revealed faint evidence of a mass involving the mid portion of the right kidney. A CT scan performed with contrast material disclosed a corresponding area in the right kidney that had a diminished attenuation coefficient and a mottled appearance of the nephrogram in comparison to normal renal parenchyma (fig. 5). An arteriogram disclosed a poorly demarcated avascular area in the center of the right kidney (fig. 6). The 670

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Defervescence occurred 2 days postoperatively and convalescence was uneventful. The patient was maintained on an aminoglycoside for several days and then started on oral ampicillin. A followup CT scan 1 year after initial diagnosis demonstrated no renal pathology. Case 4. D. P., a 26-year-old woman, presented with a history of urgency, frequency and dysuria. She gave no recent history of chills, flank pain or fever and physical examination was unremarkable. Urinalysis showed O to 2 white blood cells per high power field and a urine culture was sterile. The patient had undergone frequent urethral dilations

Fm. 1. Case l. A, CT scan through mid portion of right kidney shows rounded area of decreased attenuation (arrow) in lateral aspect of B, same slice made at narrow window width (75 EMI units) to tu,p.,uwu,t small differences in density.

FIG. 3. Case 2. A, 7-minute tomogram from IVP demonstrates focal bulbous enlargement of lower pole of right kidney and diminished filling of corresponding lower pole calix. B, 10 days after antibiotic therapy there is marked improvement in excretion and caliceal filling Minimal enlargement of lower pole remains.

FIG. 2. Followup CT scan in case 1 shows normal. right kidney 6 months after acute episode.

renal parenchyma appeared normal and there was no evidence of neovascularity. Diagnosis was renal abscess and 1½ days after transfer to this institution was done through a flank incision. An 4 X 4 cm. area of nonfluctuant, bulging renal was located the lateral margin of the kidney. not be aspirated the mass. Biopsies of this segment of the kidney disclosed marked interstitial inflammation with prominent polymorphonuclear leukocyte infiltration but no zones of liquefaction. A culture from this tissue later E.coli.

FIG. 4. Urngram in case 2 is completely normal 3 months later

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MCDONOUGH, SANDLER AND BENSON studies by us suggested that the findings were, in fact, owing to acute focal bacterial nephritis. The patient was treated with parenteral penicillin G and the symptoms resolved. She did well during the next 3 years except for 2 intervening bouts of uncomplicated cystitis. An IVP at the present evaluation exhibited no renal pathology. DISCUSSION

FIG. 5. Case 3. CT scan through mid portion ofright kidney. Nephrogram is inhomogeneous and wedged-shaped area of decreased attenuation is evident.

FIG. 6. Case 3. Nephrogram phase of selective right renal angiogram shows mottled, rounded area of decreased contrast material excretion in mid portion of kidney.

childhood for recurrent urinary tract infections. She had been hospitalized elsewhere 3 years previously with fever and right flank pain. An IVP at that time revealed a right renal mass. Ultrasound demonstrated a focal mass with diminished echogenicity in the upper pole of this kidney. Diagnosis was acute renal abscess. However, review of the

1

The distinction between acute focal bacterial nephritis and renal abscess or even tumor may be confusing and difficult. Ultrasound and CT aid in establishing the correct diagnosis. In most instances of acute focal bacterial nephritis the mass on urography is of a slightly less nephrographic density than the surrounding uninvolved renal parenchyma. In other cases the mass may be seen as a focal area of enlargement in the kidney with a density similar to that of the remaining uninvolved kidney. A combination of focal and diffuse abnormalities also has been described. 2 The lesion may be indistinguishable from that produced by a renal abscess. However, on ultrasound the lesion is typically a sonolucent, poorly marginated mass containing low-level echoes that disrupt the corticomedullary junction. On the other hand, a renal abscess differs from acute focal bacterial nephritis in that it usually contains distinct although irregular margins and usually is nearly anechoic. However, in 2 of 7 patients studied with modern gray scale equipment Lee and associates found an echogenic mass rather than the more typically found hypo-echoic lesion. 3 A CT scan also depicts the poor margination present in acute focal bacterial nephritis. Pre-contrast scanning can show the lesion to have the same or less density than normal renal parenchyma. The post-contrast scans commonly reveal a pattern of enhancement in the lesion that is patchy and inhomogeneous. A CT scan shows an abscess to be less dense than the surrounding normal renal parenchyma and a lack of enhancement with intravenous contrast material in its central portions.There is no evidence of liquefaction in acute focal bacterial nephritis in contrast to frank abscess. The distinction of acute focal bacterial nephritis from a wholly intrarenal solid tumor may be difficult at times on the basis of the radiological studies. However, the clinical situation usually strongly suggests an infectious etiology. Each of our 4 patients presented with signs and symptoms of acute pyelonephritis. Urine cultures were positive in 3 and in 1 patient a positive culture was obtained from the infected kidney at the time of operation. All patients had evidence of a renal mass on an IVP. In 1 patient ultrasound obtained at the time of infection revealed a lesion suggestive of acute focal bacterial nephritis. In 2 patients CT scans disclosed lesions with features of solid inflammatory masses. Followup IVPs in 3 patients and subsequent CT scans in 2 cases revealed resolution of the lesions without residual abnormality. In the 1 patient who underwent an operation a solid inflammatory lesion was found. A preoperative angiogram obtained in this case demonstrated the largely avascular nature of the mass but failed to show a clear demarcation of the lesion from the surrounding parenchyma, such as is seen in most cases of renal abscesses. Rosenfield and associates performed arteriography on 5 patients and demonstrated stretching and displacement of the arteries within the inflamed renal lobe, a pattern similar to that which was noted in our patient. 2 A lesion analogous to acute focal bacterial nephritis has been produced experimentally in pigs with urine infected deliberately with E. coli and in which vesicoureteral reflux was created. 4 The idea that radiographically evident reflux may be present in these patients or possibly serves as the mechanism involved in the generation of acute focal bacterial nephritis is intriguing. Such reflux could be present before infection or alternatively might be induced by a lower urinary tract infection in a patient with a marginally competent ureterovesical junction.

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ACUTE FOCAL BACTERIAL NEPHRITIS

There may well be a close relationship between acute focal bacterial nephritis and renal abscess. Acute focal bacterial nephritis could represent a relatively early stage of frank abscess formation. This contention is supported by 1 case reported previously that did progress to frank abscess formation. 3 If this is true one would expect that a certain gradation exists, with some masses having a more solid appearance while others may to have undergone more liquefaction. Nevertheless, the cm,m1c1;10•n between a clearly solid inflammatory lesion and a renal abscess is important, since the former typically responds to medical therapy and the latter typically requires surgical

REFERENCES 1. Silver, T. M., Kass, E. J., Thornbury, J. R., Konnak, J. W. and

Wolfman, M. G.: The radiological spectrum of acute phritis in adults and adolescents. Radiology, 1.18: 65, 2. Rosenfield, A. T., Glickman, M. G., Taylor, K J. W., Crade, M. and Hodson, J.: Acute focal bacterial nephritis (acute lobar nephronia). Radiology, 132: 553, 1979. 3. Lee, J. K. T., McClennan, B. L., Melson, G. L. and Stanley, Acute focal bacterial nephritis: emphasis on gray scale sm10<1raphy and computed tomography. Amer. J. Roentgen., 135: J.980. 4. Hodson, J., Maling, T. M. J., McManamon, P. J. and Lewis, M. Reflux nephropathy. Kidney Int., suppl. 4, 8: S-50, 1975.