Renal Abscesses Measuring 5 cm or Less: Outcome of Medical Treatment without Therapeutic Drainage

Renal and perirenal abscesses are uncommon disease entities resulting from infections in or around the kidneys. Furthermore, it is a diagnostic challenge for physicians. A delay in diagnosis may lead to higher morbidity and mortality.1 With the availability of computed tomography (CT) scanning and magnetic resonance imaging (MRI) in the diagnosis of renal abscesses, mortality has been reduced to 12%.2 The mainstay of treatment for renal or perinephric abscesses is adequate drainage and optimal antibiotic regimen.2 Classical management for renal abscesses includes surgical exploration, incision and drainage, or nephrectomy.3 However, minimally invasive treatment appeared in the early 1970s, and the trend toward conservative treatment was common due to the advances in imaging techniques and novel antibiotics. Several reports observed that small renal abscesses were effectively treated with a course of intravenous antibiotics.4, 5 The efficacy of conservative treatment in medium sized (3-5 cm) renal abscesses, however, has not been consistently observed across studies.2-5 Therefore, we reviewed our experience with 49 renal abscesses to investigate the characteristics and comorbidity factors of renal abscesses measuring 5 cm or less and to critically examine the effectiveness of conservative treatment.

Between February 2001 and March 2009, the records of 63 patients initially diagnosed at our hospital with renal abscesses were retrospectively reviewed. In 63 patients with renal and perirenal abscesses, 51 abscesses measured 5 cm or less. Of the 51 patients, two patients with renal abscesses underwent percutaneous abscess drainage and 49 abscesses were treated with intravenous antibiotics alone. We analyzed patient characteristics, abscess location and size, predisposing factors, clinical presentation, microbiology, laboratory data, treatment, outcome, and length of hospitalization.

Renal abscesses were diagnosed with imaging studies such as abdominal CT or MRI and only included the renal capsule and perirenal abscesses within Gerota's fascia. Those confined in the cortex, central medulla, or internal calices were considered renal abscesses while those localized between the capsule of the kidney and Gerota's fascia were identified as perirenal abscesses.6 The size of renal or perirenal abscesses was measured as the largest diameter. Abscesses with a size of 3 cm or less were defined as small, 3-5 cm as medium, and 5 cm or more as large. Patients were discharged when clinical and laboratory parameters normalized during the minimum 48 hours. Follow-up CT scans were performed in all patients to evaluate the resolution of renal lesions (range 3 to 14 weeks).

Multivariate analysis was done to determine independent risk factors for the length of hospitalization in patients with renal or perirenal abscesses.

In 1996, Siegel, et al.4 suggested an algorithmic approach to the management of renal abscesses. They reported that primary conservative management using antibiotics was recommended in small abscesses (< 3 cm) whereas drainage (percutaneous or surgical) was recommended in large abscesses (> 5 cm). Both observation protocols used were possible in medium-sized abscesses (3-5 cm). However, percutaneous abscess drainage has several complications, although uncommon, such as pyopneumothorax, bacteremia, and fistula in the gastrointestinal tract.7 Bamberger recommended avoidance of aggressive interventional or surgical treatment of renal and perinephric abscesses of 5 cm in diameter or less, which can have complete remission after antibiotic therapy.8 However, another study showed that aggressive drainage was appropriate in abscesses > 3 cm.4 The reported primary treatment of renal abscesses by size is summarized in Table 4.4, 5, 9-11 As shown in Table 4, a common treatment modality for medium-sized abscesses has not been observed across studies. We reported a 100% cure rate of small and medium renal abscesses (5 cm or less) using systemic antibiotics. In an era of improved antimicrobial treatment and support care, the rate of conservative treatment to therapeutic intervention would increase with time. However, it remains unclear under which circumstances medical management without drainage is a reasonable option. A disadvantage of medical therapy without at least diagnostic drainage is that empirical regimens could be utilized without knowledge of the offending organisms and their antimicrobial susceptibilities. Further studies are needed to distinguish the characteristics of abscesses that respond to medical management and determine the optimal duration and type of therapy.

Table 4
Reported Primary Treatment of Renal or Perinephric Abscesses by Size

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In several studies, urinary obstruction and renal stones have been reported as common predisposing conditions with an incidence of 21-50%12, 13 and 24-54%,2, 14 respectively. However, our study showed that systemic diseases such as DM (46.9%) was much more common than renal or urologic diseases such as malignancy (4.1%) or renal stones (10.2%).

In our study, patients with renal abscesses had a higher rate of E. coli infection in urine cultures, and a female predominance (91.8%) was observed. This may be a result of the development of renal abscesses via an ascending infection by organisms already isolated within the urinary tract,9 and interestingly, in Korea, use of a bidet has become widespread in recent decades. This might cause the ascending infection, especially in the relatively short urethra in females.

Lin, et al.9 reported that age over 65 years, thrombocytopenia, and abscesses without drainage were independently related to a poor outcome. This study revealed somewhat different results compared to their study. We observed that age, underlying comorbidity such as DM, and abscess size were independently related to hospital stay. This should alert physicians to the possibility of warning patients of longer hospitalization and intervention in this setting. As far as we know, this is the first study to determine the predictors of hospital stay in patients with renal or perirenal abscesses.

Limitations affecting our current findings must be considered. First, our study is non-comparative. Only 2 patients underwent percutaneous drainage, and we could not compare the outcome of antibiotics treatment alone to that of percutaneous drainage. Second, diagnostic tools such as CT or MRI scans were not performed in identical fashion. Variations across scans likely impacted the reported values of our clinical parameters. Furthermore, radiology reports were not provided by the same radiologist, and different opinions among radiologists might be embedded. Based on these results, large-scale prospective studies are needed to establish more current and reasonable guidelines for the treatment of renal or perirenal abscesses.

In conclusion, medium-sized as well as small-sized renal abscesses were successfully treated with intravenous antibiotics alone. If therapeutic drainage is believed to involve considerable risk, then intravenous antimicrobial therapy may be a good alternative treatment.