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CLINICAL AND RADIOLOGICAL FINDINGS IN PATIENTS WITH GAS FORMING RENAL ABSCESS TREATED CONSERVATIVELY
0022-5347/99/1624-1273/0 THEJOURNAL OF UROLOGY Copyright 0 1999 by AMERICAN UROLOCICAL ASSOCIATION, INC
Vol. 162. 1273-1276, October 1999 Printed i n U.S.A.
CLINICAL AND RADIOLOGICAL FINDINGS IN PATIENTS WITH GAS FORMING RENAL ABSCESS TREATED CONSERVATIVELY CHARLES D. BEST, MARTHA K. TERRIS, J. RONALD TACKER
AND
JEFFREY H. REESE
From the Departments of Urology, Santa Clara Valley Medical Center, Santa Clara and Palo Alto Veterans Medical Center, Palo Alto, California
ABSTRACT
Purpose: Emphysematous pyelonephritis in diabetics is considered a potentially lethal infection. Mortality rates of patients treated conservatively approaches 80% in some series. These patients often present with signs of sepsis or septic shock. In contrast, gas forming renal abscess is rare, with patients presenting entirely differently from those with emphysematous pyelonephritis. To our knowledge this process has been previously described only in isolated case reports. We describe a series of 5 patients with this distinct process. Materials and Methods: We reviewed the clinical and radiological features of 5 patients with gas forming renal abscesses. Results: Each patient presented with diabetes mellitus with initial blood glucose ranging from 313 to 552 mg./dl., fever (average 101F), flank or abdominal pain and pyuria. No patient had evidence of septic shock a t hospitalization. Escherichia coli was the documented organism in each case. Mild renal insufficiency was noted in most patients based on serum creatinine. Radiological evaluation revealed gas filled pockets within the renal parenchyma, which were most effectively shown by computerized tomography (CT) of the abdomen. There was no radiological evidence of pus. Percutaneous drainage of a n abscess in 1case did not produce any purulent material or alter the clinical course. Each patient responded to correction of the underlying metabolic abnormalities with intravenous antibiotics (average 23 days) followed by prolonged oral antibiotic therapy (average 9 weeks). I n contrast to the management of emphysematous pyelonephritis, surgical or percutaneous drainage was not necessary. Serial CT revealed complete resolution of gas in the parenchyma within 6 months in patients with long-term followup. Of note, gas was persistent on CT months after infection had clinically resolved. Conclusions: We describe a unique entity within the spectrum of pyelonephritis. The clinical appearance of gas forming abscesses within the renal parenchyma without liquefaction in diabetic patients was remarkably benign compared to the radiographic appearance of the disease process. Conservative management with intravenous and oral antibiotics was successful in each patient, avoiding the need for invasive intervention. KEY WORDS: abscess, treatment, antibiotics, diagnostic imaging, pyelonephritis Gas forming renal infections in diabetic patients are considered surgical emergencies. Historically, they were treated with nephrectomy or open drainage resulting in a moderate nephron salvage rate.' Recent reports suggest that percutaneous drainage may be sufficient to treat some patients with gas forming renal infections successfully.2 These infections may present as a spectrum of entities ranging from true necrotizing emphysematous pyelonephritis that requires emergency nephrectomy to discrete gas forming renal abscess that demands only conservative treatment. We have previously reported on 2 patients who presented with discrete gas forming renal abscesses which were successfully treated with antibiotic therapy alone,3 and 3 additional patients with this diagnosis have responded to conservative management (see table). Unlike classical emphysematous pyelonephritis, patients with gas forming renal abscesses present with unique clinical and radiological features that distinguish this process from the more virulent emphysematous pyelonephritis. This distinction is important in that patients with gas forming renal abscesses may be treated
with antibiotics alone. While conservative management of emphysematous pyelonephritis leads to increased mortality, it may be the treatment of choice for gas forming renal abscess. CASE HISTORIES
Case I. C. T., a 54-year-old diabetic man, was evaluated for complaints of diarrhea, left upper quadrant abdominal pain and nausea. Temperature was 100.4F and did not rise during subsequent observation. Except for mild orthostatic hypotension at presentation, the patient was hemodynamically stable throughout hospitalization. Initial laboratory studies were noteworthy for a peripheral white blood count (WBC) of 22.3 thousand per mm.3, serum creatinine 1.9 mg./dl. and serum glucose 381 mg./dl. Urine and blood cultures at hospitalization yielded Escherichia coli. Abdominal computerized tomography (CT) revealed a single, 4 cm. air filled abscess in the upper and mid pole of the left kidney with thickening of the perirenal fat (fig. 1,A). The patient was hospitalized and treated with intravenous Accepted for publication April 1, 1999. ceftriaxone for 2 weeks, during which symptoms resolved and Editor's Note: This article is the second of 5 published in white blood count decreased to 11.5 thousand per mm.3 He this issue for which category 1 CME credits can be earned. Instructions for obtaining credits are given with the ques- received an additional 2 weeks of intravenous ceftriaxone at home, followed by a 1-month course of 500 mg. oral ciprotions on pages 1450 and 1451. 1273
1274
CONSERVATIVE TREATMENT OF GAS FORMING RENAL ABSCESSES Comparison of findings in 5 patients with gas forming renal abscesses Case No.
Sex
1
2
M
F
3
57 Age (.vrs.1 54 100.4 99.8 Temperature a t hospitalization I F ) WBC ( x 10") 22 24 2.2 Serum creatinine (mg./dl.I 1.9 552 Serum glucose (mg./dl.) 381 28 12 Length of intravenous antibiotics (days) Length of oral antibiotics ~ w k s . ) 4 6 Time to CT resolution (mos.) 6 6 Urine culture yielded E. coli in all cases and no purulence was revealed on CT.
Average 4:3
53
F
M
F
48 101 13 1.4 454 11 6 5
47 100.9 19 2.1 420 14 4 5
59 102 18 1.8 313 42 18
6
53 100.8 19.2 1.9 424 21.4 7.6 5.6
FIG.1. Case 1. A, CT a t hospitalization shows large gas collection within parenchyma of left kidney. B , CT 6 months after conservative management reveals gas collection has completely resolved.
floxacin twice daily. Six months after discharge home CT revealed resolution of the abscess (fig. 1, B ) . Serum creatinine at 10 months was 1.4 mg./dl. Case 2. F. C., a 57-year-old woman with a history of insulin dependent diabetes, presented with complaints of persistent fever and chills, despite treatment for 1 week with oral antibiotics in Mexico for presumed kidney infection. Admission laboratory studies revealed peripheral WBC 24.3 thousand per ~nm.~., serum glucose 552 mg./dl. and serum creatinine 2.2 mg./dl. Urinalysis was consistent with a urinary tract infection. The patient had a benign abdomen on examination and only a low grade fever (99.8F) at hospitalization. She was placed on intravenous ticarcillin clavulanate with prompt resolution of symptoms and decreased peripheral
WBC. Renal ultrasound revealed findings suspicious for air within the parenchyma of the right kidney. CT of the abdomen showed several gas filled abscesses within the parenchyma (fig. 2, A). Urine cultures yielded E. coli. The hospital course was uneventful with resolution of leukocytosis and a followup creatinine of 1.4 mg./dl. Followup CT 4 days later showed diminished but persistent gas in the right kidney (fig. 2, B).The patient completed a 2-week course of intravenous antibiotics and then switched t o oral cephalexin. Repeat CT at the time of discharge home revealed only trace amounts of gas in the affected kidney. Case 3. J. G., a 48-year-old diabetic woman, presented with progressive lethargy for 3 months, and subjective fevers and chills. Prior neurological evaluation elsewhere, including
FIG.2. Case 2. A, CT at hospitalization reveals several gas filled collections within parenchyma of right kidney and no fluid collections. B , CT after 4 days of conservative treatment shows significant resolution of gas collections.
CONSERVATIVE TREATMENT OF GAS FORMING RENAL ABSCESSES head CT, was negative. She denied voiding difficulties, dysuria or pyuria. Evaluation was performed at a satellite outpatient clinic locally, and blood and urine cultures yielded E. coli. She was subsequently hospitalized with a temperature of 101F, and physical examination was unremarkable except for mild left flank tenderness and global hyporeflexia. Additional laboratory studies included serum glucose 454 mg./dl., serum creatinine 1.4 mg./dl. and WBC 13 thousand per mm.3 She was started on intravenous cefotetan. Abdominal CT revealed a 5 x 10 cm. left renal abscess with gas only and no fluid as well as a smaller gas filled splenic abscess (fig. 3, A). Percutaneous aspiration of the splenic abscess revealed 30 cc purulent material and gas. Cultures from this abscess yielded E. coli. During the hospital course, defervescence occurred, symptoms improved and creatinine decreased by hospital day 7 to 1.0 mg./dl. After 11 days of intravenous cefotetan the patient was discharged home and continued treatment with 6 weeks of oral ciprofloxacin. She remained asymptomatic and CT a t 5 months demonstrated no renal abscess (fig. 3 , B). A diuretic renogram at 6 months revealed slightly diminished function on the left side but there was no prior study for comparison. DISCUSSION
Gas forming infections represent a small percentage of all bacterial infections of the kidney. The spectrum of gas forming infections of the upper urinary tract includes emphysematous pyelonephritis or emphysematous pyelitis and gas forming abscesses. Pyelitis only involves the collecting system and not the parenchyma. Emphysematous pyelonephritis is a diffuse necrotizing infection characterized radiographically by multiple small bubbles of gas within the parenchyma and perinephric space. Patients often present in septic shock and require emergency surgery. Conservative therapy in these patients has been reported to carry up to an 80% mortality rate.4 Our patients presented with isolated, large parenchymal gas forming lesions and without diffuse renal destruction radiographically. The majority presenting with gas forming renal abscesses are moderately ill but not critically septic, as may be seen with true emphysematous pyelonephritis. The radiographic was far more severe than the clinical appearance of our patients. The severity of such infectious processes may compound other medical problems, particularly electrolyte abnormalities, dehydration and acidosis. Our patients presented mostly with urinary tract infections and without evidence of obstruction of the urinary collecting system. Some patients may have costovertebral angle tenderness. Emphysematous pyelonephritis presents in a similar fashion. Plain film radiography may show obscuring of the psoas
,
1275
shadow and air in the region of the renal unit. Excretory urography may be consistent with a nonfunctioning kidney or mass in the kidney but will also reveal obstruction or calculi. This study is not specific enough to lead to an accurate diagnosis. Ultrasonography has been shown to diagnose renal abscesses adequately in most circumstances5 but it cannot accurately measure the depth of gas collections.6 CT is the ideal diagnostic aid as it can confirm the diagnosis, can effectively demonstrate location and extension of the process, and may also accurately diagnose associated complications, such as subphrenic or splenic abscesses, papillary necrosis or retroperitoneal involvement. On CT gas forming renal abscesses appear as discrete gas pockets without purulent material within the renal parenchyma. As with any significant infection, there is potential spread to adjacent tissue. Gas forming renal abscesses are not necessarily associated with diffuse renal destruction. In contrast, the prognosis for renal function is poor in cases of emphysematous pyelonephritis. The differential diagnosis should also include an infected renal cyst or tumor. Infected renal cysts require percutaneous drainage t o treat the infection adequately.7 E. coli, a facultative anaerobe, was the documented organism in each of our patients. This bacterium is capable of metabolizing glucose to form gas within the tissue. Increased production of gas by rapid tissue catabolism and impaired transportation of gas are other proposed mechanisms for gas abscess formation. High tissue glucose levels favor bacterial growth and gas production, which explains why this entity has only been documented in diabetic patients. Diabetes also predisposes patients to intrinsic vascular disease leading to papillary necrosis and renal infections. E. coli has been cited as responsible for other gas forming infections.s.9 All of our patients with gas forming renal abscesses exhibited an intense localized infection of the parenchyma, without a large amount of tissue destruction or purulent material.3 This localization could also account for the benign clinical course of gas forming renal abscess compared to emphysematous pyelonephritis. Patients with acute pyelonephritis usually begin to respond to antibiotic therapy within 3 to 5 days of treatment. Normally with treatment one would expect gas within the tissues to be rapidly absorbed in 24 to 48 hours. Our cases were unusual in this aspect since gas persisted radiographically for months after they had been treated clinically, which may be due to ongoing subclinical infection or, more likely, an encapsulation that decreases the ability of gas to diffuse rapidly through the tissues. Nonresponders generally are evaluated sonographically or with CT to exclude from diagnosis other causes, such as hydronephrosis, infected tumor, infected cysts or perinephric and parenchymal abscesses.
FIG.3. Case 3. A, CT reveals large gas collection without fluid in left kidney, no prirenal inflammation and early excretion of contrast material, implying reasonable function. B , CT 5 months aRer treatment with antibiotics alone shows complete resolution of gas collections.
1276
CONSERVATlVE TREATMENT OF GAS FORMING RENAL ABSCESSES
Ow patients were treated with antibiotics alone, except one who underwent percutaneous drainage of a splenic abscess. The decision to avoid surgical drainage was based primarily on the relatively benign clinical appearance, despite impressive disease radiographically. None of our patients demonstrated any evidence of hemodynamic instability. Recent reports have noted probable gas forming renal abscesses treated conservatively, suggesting that this entity is more common than previously recognized.2.5,10 Chen et a1 described the successful management of emphysematous pyelonephritis with percutaneous drainage.2 Although many of their cases presented with more severe infections than ours, some may have been in the category of gas forming renal abscess. Siegel et a1 reported a comparison of patients with renal abscesses. Their cases were similar in presentation to ours, except for purulent material within the abscess. They reported a 100%kidney salvage rate in patients treated with antibiotics alone, although renal function was not reported. Their overall cure rate for this conservative management was 73%, with a 25% mortality rate.10 Wan et al described patients who, although radiographically similar to ours, were more clinically ill and did poorly with conservative management.” Consequently, clinical presentation should be considered in determining management strategies. CONCLUSIONS
We define gas forming renal abscess as occurring in diabetic patients with an E. coli urinary tract infection who present with mild fever and flank pain, and are hemodynamically stable. CT findings are consistent with discrete gas pockets within the renal parenchyma without pus. These patients respond quickly to antibiotics but abscesses are slow to resolve radiographically. We suggest initial management with nephron sparing intravenous antibiotics with effective gram-negative coverage and fluid resuscitation. Correcting the underlying hyperglycemia and electrolyte imbalances will also be crucial to prompt - recovery. Once the acute clinical disease process has been stabilized a prolonged course of
oral antibiotics should be provided until complete resolution of the gas entity is seen radiographically. Our patients were treated uniformly with ciprofloxacin, a fluoroquinolone. Surgical therapy may offer little benefit in these cases and may result in greater nephron loss. In any patient who worsens or does not improve surgical or percutaneous intervention is warranted. REFERENCES
1. Patel, N. P., Lavengood, R. W., Fernandes, M., Ward, J. N. and
Walzak. M. P.: Gas-formina infections in eenitourinarv tract. Urology, 3 9 341, 1992. 2. Chen. M. T.. Huane, C. N.. Chou, Y.-H., Huane, C.-H.. Chiana. C.-P. and Liu, G.rC.: Percutaneous drainage in the treatmeit of emphysematous pyelonephritis: 10-year experience. J. Urol., 157: 1569, 1997. 3. Nickas, M. E., Reese, J. H. and Anderson, R. U.: Medical therapy alone for the treatment of eas formine intrarenal abscess. J. Urol., 151: 398, 1994. 4. Klein. F. A.. Smith. M. J.. Vick. C. W.. I11 and Schneider. V.: Emphysematous pyelonephritis: diagnosis and treatment. S. Med. J., 7 9 41, 1986. 5. Wippermann, C. F., Schofer, O., Beetz, R., Schumacher, R., Schweden, F., Riedmiller, H., Buttner, J.: Renal abscess in childhood: diagnostic and therapeutic progress. Ped. Inf. Dis. J., 1 0 446, 1991. 6. Hoddick. W.. Jefiev. R. B.. Goldbere. H. I.. Federle. M. P. and Laing,’F.C.: CT and sonography orsevere’renal and perirenal infections. AJR, 1 4 0 517, 1983. 7. Frishman, E., Orron, D. E., Heiman, Z., Kessler,A., Kaver, I. and Graif, M.: Infected renal cysts: sonographic diagnosis and management. J. Ultrasound Med., 1 3 7, 1994. 8. Ho K. M. and Sole, G. M.: Pneumaturia due to gas-producing E. coli and urinary statsis. Br. J. Urol., 7 3 588, 1994. 9. Corder, A. P.: Renal abscess with gas formation secondary to acute appendicitis. Brit. J. Urol., 5 9 90, 1987. 10. Siegel, J. F., Smith, A. and Moldwin, R.: Minimally invasive treatment of renal abscess. J. Urol., 155 52, 1996. 11. Wan, Y. L., Lo, S.-K., Bullard, M. J., Chang, P.-L. and Lee, T.-Y.: Predictors of outcome in emphysematous pyelonephritis. J. Urol., 159 369, 1998. I
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Vol. 162. 1273-1276, October 1999 Printed i n U.S.A.
CLINICAL AND RADIOLOGICAL FINDINGS IN PATIENTS WITH GAS FORMING RENAL ABSCESS TREATED CONSERVATIVELY CHARLES D. BEST, MARTHA K. TERRIS, J. RONALD TACKER
AND
JEFFREY H. REESE
From the Departments of Urology, Santa Clara Valley Medical Center, Santa Clara and Palo Alto Veterans Medical Center, Palo Alto, California
ABSTRACT
Purpose: Emphysematous pyelonephritis in diabetics is considered a potentially lethal infection. Mortality rates of patients treated conservatively approaches 80% in some series. These patients often present with signs of sepsis or septic shock. In contrast, gas forming renal abscess is rare, with patients presenting entirely differently from those with emphysematous pyelonephritis. To our knowledge this process has been previously described only in isolated case reports. We describe a series of 5 patients with this distinct process. Materials and Methods: We reviewed the clinical and radiological features of 5 patients with gas forming renal abscesses. Results: Each patient presented with diabetes mellitus with initial blood glucose ranging from 313 to 552 mg./dl., fever (average 101F), flank or abdominal pain and pyuria. No patient had evidence of septic shock a t hospitalization. Escherichia coli was the documented organism in each case. Mild renal insufficiency was noted in most patients based on serum creatinine. Radiological evaluation revealed gas filled pockets within the renal parenchyma, which were most effectively shown by computerized tomography (CT) of the abdomen. There was no radiological evidence of pus. Percutaneous drainage of a n abscess in 1case did not produce any purulent material or alter the clinical course. Each patient responded to correction of the underlying metabolic abnormalities with intravenous antibiotics (average 23 days) followed by prolonged oral antibiotic therapy (average 9 weeks). I n contrast to the management of emphysematous pyelonephritis, surgical or percutaneous drainage was not necessary. Serial CT revealed complete resolution of gas in the parenchyma within 6 months in patients with long-term followup. Of note, gas was persistent on CT months after infection had clinically resolved. Conclusions: We describe a unique entity within the spectrum of pyelonephritis. The clinical appearance of gas forming abscesses within the renal parenchyma without liquefaction in diabetic patients was remarkably benign compared to the radiographic appearance of the disease process. Conservative management with intravenous and oral antibiotics was successful in each patient, avoiding the need for invasive intervention. KEY WORDS: abscess, treatment, antibiotics, diagnostic imaging, pyelonephritis Gas forming renal infections in diabetic patients are considered surgical emergencies. Historically, they were treated with nephrectomy or open drainage resulting in a moderate nephron salvage rate.' Recent reports suggest that percutaneous drainage may be sufficient to treat some patients with gas forming renal infections successfully.2 These infections may present as a spectrum of entities ranging from true necrotizing emphysematous pyelonephritis that requires emergency nephrectomy to discrete gas forming renal abscess that demands only conservative treatment. We have previously reported on 2 patients who presented with discrete gas forming renal abscesses which were successfully treated with antibiotic therapy alone,3 and 3 additional patients with this diagnosis have responded to conservative management (see table). Unlike classical emphysematous pyelonephritis, patients with gas forming renal abscesses present with unique clinical and radiological features that distinguish this process from the more virulent emphysematous pyelonephritis. This distinction is important in that patients with gas forming renal abscesses may be treated
with antibiotics alone. While conservative management of emphysematous pyelonephritis leads to increased mortality, it may be the treatment of choice for gas forming renal abscess. CASE HISTORIES
Case I. C. T., a 54-year-old diabetic man, was evaluated for complaints of diarrhea, left upper quadrant abdominal pain and nausea. Temperature was 100.4F and did not rise during subsequent observation. Except for mild orthostatic hypotension at presentation, the patient was hemodynamically stable throughout hospitalization. Initial laboratory studies were noteworthy for a peripheral white blood count (WBC) of 22.3 thousand per mm.3, serum creatinine 1.9 mg./dl. and serum glucose 381 mg./dl. Urine and blood cultures at hospitalization yielded Escherichia coli. Abdominal computerized tomography (CT) revealed a single, 4 cm. air filled abscess in the upper and mid pole of the left kidney with thickening of the perirenal fat (fig. 1,A). The patient was hospitalized and treated with intravenous Accepted for publication April 1, 1999. ceftriaxone for 2 weeks, during which symptoms resolved and Editor's Note: This article is the second of 5 published in white blood count decreased to 11.5 thousand per mm.3 He this issue for which category 1 CME credits can be earned. Instructions for obtaining credits are given with the ques- received an additional 2 weeks of intravenous ceftriaxone at home, followed by a 1-month course of 500 mg. oral ciprotions on pages 1450 and 1451. 1273
1274
CONSERVATIVE TREATMENT OF GAS FORMING RENAL ABSCESSES Comparison of findings in 5 patients with gas forming renal abscesses Case No.
Sex
1
2
M
F
3
57 Age (.vrs.1 54 100.4 99.8 Temperature a t hospitalization I F ) WBC ( x 10") 22 24 2.2 Serum creatinine (mg./dl.I 1.9 552 Serum glucose (mg./dl.) 381 28 12 Length of intravenous antibiotics (days) Length of oral antibiotics ~ w k s . ) 4 6 Time to CT resolution (mos.) 6 6 Urine culture yielded E. coli in all cases and no purulence was revealed on CT.
Average 4:3
53
F
M
F
48 101 13 1.4 454 11 6 5
47 100.9 19 2.1 420 14 4 5
59 102 18 1.8 313 42 18
6
53 100.8 19.2 1.9 424 21.4 7.6 5.6
FIG.1. Case 1. A, CT a t hospitalization shows large gas collection within parenchyma of left kidney. B , CT 6 months after conservative management reveals gas collection has completely resolved.
floxacin twice daily. Six months after discharge home CT revealed resolution of the abscess (fig. 1, B ) . Serum creatinine at 10 months was 1.4 mg./dl. Case 2. F. C., a 57-year-old woman with a history of insulin dependent diabetes, presented with complaints of persistent fever and chills, despite treatment for 1 week with oral antibiotics in Mexico for presumed kidney infection. Admission laboratory studies revealed peripheral WBC 24.3 thousand per ~nm.~., serum glucose 552 mg./dl. and serum creatinine 2.2 mg./dl. Urinalysis was consistent with a urinary tract infection. The patient had a benign abdomen on examination and only a low grade fever (99.8F) at hospitalization. She was placed on intravenous ticarcillin clavulanate with prompt resolution of symptoms and decreased peripheral
WBC. Renal ultrasound revealed findings suspicious for air within the parenchyma of the right kidney. CT of the abdomen showed several gas filled abscesses within the parenchyma (fig. 2, A). Urine cultures yielded E. coli. The hospital course was uneventful with resolution of leukocytosis and a followup creatinine of 1.4 mg./dl. Followup CT 4 days later showed diminished but persistent gas in the right kidney (fig. 2, B).The patient completed a 2-week course of intravenous antibiotics and then switched t o oral cephalexin. Repeat CT at the time of discharge home revealed only trace amounts of gas in the affected kidney. Case 3. J. G., a 48-year-old diabetic woman, presented with progressive lethargy for 3 months, and subjective fevers and chills. Prior neurological evaluation elsewhere, including
FIG.2. Case 2. A, CT at hospitalization reveals several gas filled collections within parenchyma of right kidney and no fluid collections. B , CT after 4 days of conservative treatment shows significant resolution of gas collections.
CONSERVATIVE TREATMENT OF GAS FORMING RENAL ABSCESSES head CT, was negative. She denied voiding difficulties, dysuria or pyuria. Evaluation was performed at a satellite outpatient clinic locally, and blood and urine cultures yielded E. coli. She was subsequently hospitalized with a temperature of 101F, and physical examination was unremarkable except for mild left flank tenderness and global hyporeflexia. Additional laboratory studies included serum glucose 454 mg./dl., serum creatinine 1.4 mg./dl. and WBC 13 thousand per mm.3 She was started on intravenous cefotetan. Abdominal CT revealed a 5 x 10 cm. left renal abscess with gas only and no fluid as well as a smaller gas filled splenic abscess (fig. 3, A). Percutaneous aspiration of the splenic abscess revealed 30 cc purulent material and gas. Cultures from this abscess yielded E. coli. During the hospital course, defervescence occurred, symptoms improved and creatinine decreased by hospital day 7 to 1.0 mg./dl. After 11 days of intravenous cefotetan the patient was discharged home and continued treatment with 6 weeks of oral ciprofloxacin. She remained asymptomatic and CT a t 5 months demonstrated no renal abscess (fig. 3 , B). A diuretic renogram at 6 months revealed slightly diminished function on the left side but there was no prior study for comparison. DISCUSSION
Gas forming infections represent a small percentage of all bacterial infections of the kidney. The spectrum of gas forming infections of the upper urinary tract includes emphysematous pyelonephritis or emphysematous pyelitis and gas forming abscesses. Pyelitis only involves the collecting system and not the parenchyma. Emphysematous pyelonephritis is a diffuse necrotizing infection characterized radiographically by multiple small bubbles of gas within the parenchyma and perinephric space. Patients often present in septic shock and require emergency surgery. Conservative therapy in these patients has been reported to carry up to an 80% mortality rate.4 Our patients presented with isolated, large parenchymal gas forming lesions and without diffuse renal destruction radiographically. The majority presenting with gas forming renal abscesses are moderately ill but not critically septic, as may be seen with true emphysematous pyelonephritis. The radiographic was far more severe than the clinical appearance of our patients. The severity of such infectious processes may compound other medical problems, particularly electrolyte abnormalities, dehydration and acidosis. Our patients presented mostly with urinary tract infections and without evidence of obstruction of the urinary collecting system. Some patients may have costovertebral angle tenderness. Emphysematous pyelonephritis presents in a similar fashion. Plain film radiography may show obscuring of the psoas
,
1275
shadow and air in the region of the renal unit. Excretory urography may be consistent with a nonfunctioning kidney or mass in the kidney but will also reveal obstruction or calculi. This study is not specific enough to lead to an accurate diagnosis. Ultrasonography has been shown to diagnose renal abscesses adequately in most circumstances5 but it cannot accurately measure the depth of gas collections.6 CT is the ideal diagnostic aid as it can confirm the diagnosis, can effectively demonstrate location and extension of the process, and may also accurately diagnose associated complications, such as subphrenic or splenic abscesses, papillary necrosis or retroperitoneal involvement. On CT gas forming renal abscesses appear as discrete gas pockets without purulent material within the renal parenchyma. As with any significant infection, there is potential spread to adjacent tissue. Gas forming renal abscesses are not necessarily associated with diffuse renal destruction. In contrast, the prognosis for renal function is poor in cases of emphysematous pyelonephritis. The differential diagnosis should also include an infected renal cyst or tumor. Infected renal cysts require percutaneous drainage t o treat the infection adequately.7 E. coli, a facultative anaerobe, was the documented organism in each of our patients. This bacterium is capable of metabolizing glucose to form gas within the tissue. Increased production of gas by rapid tissue catabolism and impaired transportation of gas are other proposed mechanisms for gas abscess formation. High tissue glucose levels favor bacterial growth and gas production, which explains why this entity has only been documented in diabetic patients. Diabetes also predisposes patients to intrinsic vascular disease leading to papillary necrosis and renal infections. E. coli has been cited as responsible for other gas forming infections.s.9 All of our patients with gas forming renal abscesses exhibited an intense localized infection of the parenchyma, without a large amount of tissue destruction or purulent material.3 This localization could also account for the benign clinical course of gas forming renal abscess compared to emphysematous pyelonephritis. Patients with acute pyelonephritis usually begin to respond to antibiotic therapy within 3 to 5 days of treatment. Normally with treatment one would expect gas within the tissues to be rapidly absorbed in 24 to 48 hours. Our cases were unusual in this aspect since gas persisted radiographically for months after they had been treated clinically, which may be due to ongoing subclinical infection or, more likely, an encapsulation that decreases the ability of gas to diffuse rapidly through the tissues. Nonresponders generally are evaluated sonographically or with CT to exclude from diagnosis other causes, such as hydronephrosis, infected tumor, infected cysts or perinephric and parenchymal abscesses.
FIG.3. Case 3. A, CT reveals large gas collection without fluid in left kidney, no prirenal inflammation and early excretion of contrast material, implying reasonable function. B , CT 5 months aRer treatment with antibiotics alone shows complete resolution of gas collections.
1276
CONSERVATlVE TREATMENT OF GAS FORMING RENAL ABSCESSES
Ow patients were treated with antibiotics alone, except one who underwent percutaneous drainage of a splenic abscess. The decision to avoid surgical drainage was based primarily on the relatively benign clinical appearance, despite impressive disease radiographically. None of our patients demonstrated any evidence of hemodynamic instability. Recent reports have noted probable gas forming renal abscesses treated conservatively, suggesting that this entity is more common than previously recognized.2.5,10 Chen et a1 described the successful management of emphysematous pyelonephritis with percutaneous drainage.2 Although many of their cases presented with more severe infections than ours, some may have been in the category of gas forming renal abscess. Siegel et a1 reported a comparison of patients with renal abscesses. Their cases were similar in presentation to ours, except for purulent material within the abscess. They reported a 100%kidney salvage rate in patients treated with antibiotics alone, although renal function was not reported. Their overall cure rate for this conservative management was 73%, with a 25% mortality rate.10 Wan et al described patients who, although radiographically similar to ours, were more clinically ill and did poorly with conservative management.” Consequently, clinical presentation should be considered in determining management strategies. CONCLUSIONS
We define gas forming renal abscess as occurring in diabetic patients with an E. coli urinary tract infection who present with mild fever and flank pain, and are hemodynamically stable. CT findings are consistent with discrete gas pockets within the renal parenchyma without pus. These patients respond quickly to antibiotics but abscesses are slow to resolve radiographically. We suggest initial management with nephron sparing intravenous antibiotics with effective gram-negative coverage and fluid resuscitation. Correcting the underlying hyperglycemia and electrolyte imbalances will also be crucial to prompt - recovery. Once the acute clinical disease process has been stabilized a prolonged course of
oral antibiotics should be provided until complete resolution of the gas entity is seen radiographically. Our patients were treated uniformly with ciprofloxacin, a fluoroquinolone. Surgical therapy may offer little benefit in these cases and may result in greater nephron loss. In any patient who worsens or does not improve surgical or percutaneous intervention is warranted. REFERENCES
1. Patel, N. P., Lavengood, R. W., Fernandes, M., Ward, J. N. and
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