Awareness to EPN diagnosis and proper management is required due to life-threatening nature of associated septic complications. Proper initiation of medical treatment using adequate intravenous fluid, antibiotics in addition to electrolyte resuscitation and glycemic control can be helpful. Further treatment is either to continue conservative medical treatment with antibiotics alone, drainage with PCD or ureteral stent under the umbrella of antibiotic therapy or urgent nephrectomy may be required according the clinical situation and the disease severity.
The management of EPN has been progressed from invasive approach to more conservative treatment. Historically, Ahlering et al.  reported higher mortality rate among patients with EPN managed by urgent nephrectomy reaching 42%. Recently, PCD becomes one of the most effective treatment for EPN in association with medical management. This combination lowers the risk of mortality as a rapid noninvasive drainage method with preserving renal units.
In a retrospective study, it was reported that the successful EPN management with antibiotics alone treatment was noted in 40%, and in combined medical treatment with PCD drainage, treatment was successful in 80%. Conservative management failure was noted with associated clinical risk factors as thrombocytopenia, shock, and hemodialysis. In the absence of the previously mentioned risk factors, the success rate with conservative management was 100% .
Huang and Tseng  reported that conservative management could be successful in case of mild cases (class I and class II) EPN in addition to massive EPN (class III and IV) with < 2 risk factors (thrombocytopenia, increased serum creatinine, shock and confusion) . In a previous multicenter study, it was reported that medical management success was observed in 93.3% of patients (14 out of 15 patients) . In another study, the failure rate of conservative management was observed in nearly one third (32.6%) of patients (14/43). Severe hypoalbuminemia, renal injury with hemodialysis, and polymicrobial infections were significantly associated with failure of conservative treatment .
In our study, success rate of conservative medical management was observed in only 18.5% of total included patients. Lower rate of medical management success may be related to increase the incidence of drug resistance due to increasing the global use of antibiotics before admission. By other words, the causative bacteria that produce extended‑spectrum beta‑lactamase (ESBL) can reduce the efficacy third generation cephalosporins and make medical treatment alone usually ineffective .
Vast of the previous studies discussed mainly patient’s clinical status in addition to laboratory findings at the time of admission and their relationship with conservative management success or failure. On contrary, the relationship between CT-based radiological findings and treatment outcome is seldom discussed and is still a matter of debate.
Huang and Tseng  noted that higher mortality correlated with higher EPN stage. Furthermore, Falagas et al.  concluded that bilateral renal affection and EPN type I category (according to Wan radiological classification) were associated with higher mortality. In another study, it was concluded that EPN staging of 3B or 4 was the most reliable predictor of poor outcome . On the other hand, some authors did not find any correlation between radiological staging and initial success with conservative management . Boakes et al.  suggested that radiological grade of EPN alone was not sufficient to determine the pattern of treatment. The same conclusion was adopted by other studies [14, 15].
Subsequently, air locules volume calculation at admission can be a reliable marker for disease severity. As postulated that the mechanism of gas formation in EPN is “the gas chamber theory”. This theory was based on the presence of gas-forming organisms, poor diabetic control, and poor renal vascularity in addition to immune insufficiency . Increased the volume and the number of renal air locules may be linked to the severity of EPN infection, increased the bacterial load and impaired glucose control.
In a previous study, Elbaset et al.  documented that higher air locules volume may be associated with different drainage methods failure (either PCD or ureteral stent) and poor clinical outcome . In our study, lower air locules volume ≤ 54 cc3 was a predictor for conservative medical treatment success. In the latter group, the majority of patients were presented with lower EPN staging (EPN stage I and II), only six patients presented with uncontrolled diabetes, the majority of isolated culture was E.coli and the minority was polymicrobial infection, in addition the total leukocytic count was lower in patients with successful conservative treatment compared with patients who failed conservative treatment. All previous clinical and laboratory data, while they are statistically insignificant, indicate that the load of infection was lower in patients with successful conservative management and may be reflected by lower air locules volume in affected renal unit.
The presence of hydronephrosis and urinary stasis provide the time and opportunity for bacteria to adhere to the urinary tract epithelium, multiply, and infect the host . The presence of hydronephrosis increase the risk of gas chamber theory by increased the pelvicalyceal system pressure and compromised renal circulation with impaired gas transportation . In the absence of stone obstruction, necrosis of renal tissue may predispose to more pelvicalyceal system obstruction which by its turn increase the rate of infection . In-line with these theories, we found that the absence of hydronephrosis was a predictor for conservative management success.
The main limitation is the retrospective nature of the study with inherent selection bias. Small sample size is another limitation. In spite of these limitations, our study highlights the importance of CT markers for patients who can get benefit from medical management safely without time delay without the need for urinary drainage. Further studies are needed to confirm our findings.