FINDINGS: Mild hydronephrosis and air in the renal collecting system
DIAGNOSIS: Emphysematous Pyelonephritis

This patient has hyperechogenicity, subtle ring-down reverberation, and dirty shadowing of the renal pelvis suggesting air in the renal collecting system. He was started on IVF, imipenem, and an insulin drip for sepsis in the setting of AKI and DKA.

The diagnosis of emphysematous pyelonephritis and emphysematous cystitis were confirmed by both technician-performed renal ultrasound (Figure 1) and CT (Figure 2), which is considered the gold standard for diagnosis [1,3]. Ultrasound is not consistently effective at demonstrating gas in the renal parenchyma, being only accurate in 50% of cases per one report [2]. Two signs to look for include dirty shadowing and ring-down reverberation artifact.

The finding of hydronephrosis is common in transplanted kidneys and can be seen in this patient's ultrasound (Figure 3). Typically, hydronephrosis slowly resolves after transplant, but mild dilation can be permanent due to a denervated collecting system or bladder dysfunction. However, hydronephrosis may be the result of renal calculi, pyonephrosis, clot, ureteral strictures, or urothelial neoplasm [4]. Ultrasound has up to 94% specificity for identifying moderate to severe hydronephrosis and can help direct initial management [5].

Emphysematous pyelonephritis presents similarly to severe pyelonephritis, but patients are often very ill, and imaging demonstrates the presence of gas in the renal parenchyma, collecting system, or perinephric tissue [1]. Up to 95% of patients have a history of uncontrolled DM [3]. DKA is also an important predictor of increased mortality for these patients [2]. A transplanted kidney is at higher risk of infection spreading due to lack of investing fascia [1].

Emphysematous pyelonephritis in a renal allograft with concurrent emphysematous cystitis is a rarely reported condition. However, evidence suggests benefit of additional interventions, such as percutaneous drainage of abscesses compared to treatment with antibiotics alone [2,6,7]. It is important to evaluate for findings suggesting air in the collecting system in high-risk patients and know the next steps in management.

Figure 1. CT abdomen pelvis demonstrating emphysematous pyelonephritis (arrow) and emphysematous cystitis.

Figure 2. Ultrasound of transplanted kidney showing hyperechogenicity of collecting system (arrows) with ring-down reverberation artifact (star).