CME IN IMAGES

Year : 2017  |  Volume : 15  |  Issue : 3  |  Page : 245-246

An airy phenomenon

Anna Valson
Department of Nephrology, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
Anna Valson
Department of Nephrology, Christian Medical College, Vellore  -  632  004, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/cmi.cmi_50_17

Introduction

Figure 1: Ultrasound kidney-ureter-bladder of the patient. Click here to view

Figure 2: Noncontrast computed tomography kidney-ureter-bladder of the patient. Click here to view

Questions

1. Describe the findings on the ultrasound KUB and CT KUB
2. What are the common predisposing factors for this condition?
3. What is its pathophysiology?
4. How is this condition classified, based on radiological appearance?
5. How is this condition managed?

Answers

1. The ultrasound KUB of the left kidney shows “dirty” distal acoustic shadowing (white arrow) caused by intrarenal air pockets, that are seen as echogenic foci (blue arrow).(This is in contrast to the 'clean' or echo free shadowing caused by kidney stones). CT KUB shows an enlarged left kidney with presence of intraparenchymal air in the anterior and lateral cortex and extension of air into the perinephric space (indicated by an arrow). This condition, in which a necrotizing infection of the renal parenchyma produces intrarenal suppuration and gas formation, is called emphysematous pyelonephritis (EPN)
2. Diabetes, especially diabetes with poor glycemic control (HbA1C >8%) is the most important risk factor for EPN, accounting for 85%–96% of cases. Other risk factors include urinary tract obstruction, renal calculi, polycystic kidney disease, female gender (75% cases occur in females, who are in general, more prone to urinary tract infection), and immunocompromised patients such as renal transplant recipients ^[1],[2]
3. EPN is caused by pathogenic gas forming bacteria such as Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Pseudomonas aeruginosa which are capable of mixed acid fermentation. In immunocompromised hosts (as for example, this lady with long standing, poorly managed diabetes), these organisms are able to multiply prolifically, and in a hyperglycemic environment (seen in diabetes) fermentation of glucose produces carbon dioxide and hydrogen gas. Due to impaired microcirculation secondary to inflammation, microangiopathy or urinary tract obstruction, gas, which would have normally been reabsorbed by the renal vasculature, accumulates.^[3] The left kidney is more commonly involved than the right (52%), and only 10% cases are bilateral ^[1]
4. Based on CT findings, EPN is classified as follows:^[3] Class 1 – when gas is present in the collecting system of the kidney alone, Class 2 – when gas is present in the renal parenchyma but does not extend into the extrarenal space, Class 3a – extension of gas into the perinephric space, Class 3b – extension of gas into the pararenal space, Class 4 – bilateral EPN or EPN in a solitary kidney. This patient had Class 3a EPN. Further, there are two types of EPN described, which have prognostic relevance.^[4] Type 1 EPN has predominantly renal necrosis (>1/3 of renal parenchyma) with absence of intrarenal or perinephric fluid collections on CT and presence of streaky/mottled gas shadows, and is also called “dry EPN.” This is less common, but has a higher mortality and a more fulminant course. Type 2 EPN, also called “wet EPN,” is characterized by renal or perinephric fluid collection with bubbly or loculated gas shadows in the parenchyma or collecting system, as was seen in this patient. It has a better prognosis
5. Risk factors for poor outcome in patients with EPN include Type 1 EPN, Class 3 and 4 EPN, thrombocytopenia, elevated serum creatinine (>1.4 mg/dL), shock and altered sensorium.^[3],[4] The three treatment modalities available include IV antibiotics alone, IV antibiotics with percutaneous drainage (PCD) and in refractory cases, nephrectomy. Mortality is least for patients undergoing PCD, which is now part of first line treatment for EPN.^[1],[2] Nephrectomy is reserved for patients with extensive or fulminating disease, or those not responding to antibiotics and PCD. This patient received broad spectrum antibiotics and PCD and renal function reached a nadir of 1.3 mg/dL after treatment.

References

1.	Aboumarzouk OM, Hughes O, Narahari K, Coulthard R, Kynaston H, Chlosta P, et al. Emphysematous pyelonephritis: Time for a management plan with an evidence-based approach. Arab J Urol 2014;12:106-15.   [PUBMED]
2.	Somani BK, Nabi G, Thorpe P, Hussey J, Cook J, N'Dow J; ABACUS Research Group. Is percutaneous drainage the new gold standard in the management of emphysematous pyelonephritis? Evidence from a systematic review. J Urol 2008;179:1844-9.
3.	Huang JJ, Tseng CC. Emphysematous pyelonephritis: Clinicoradiological classification, management, prognosis, and pathogenesis. Arch Intern Med 2000;160:797-805.   [PUBMED]
4.	Wan YL, Lo SK, Bullard MJ, Chang PL, Lee TY. Predictors of outcome in emphysematous pyelonephritis. J Urol 1998;159:369-73.   [PUBMED]