Emphysematous pyelonephritis

Clinical History

The patient, a diabetic, developed septic shock within 48 hours after the diagnosis of acute pyelonephritis.

Imaging Findings

The patient, who had a history of poorly controlled diabetes mellitus, hypertension, chronic kidney failure and asthma, was admitted to the intensive care unit (ICU) of our hospital with confusion, hypoxia, and peripheral circulatory collapse (systolic arterial pressure <80 mmHg, pulse rate >120/min).

Two days before admission the patient had visited the outpatient department of another hospital because of fever and left flank pain. Ultrasonography revealed a left upper ureter dilatation and ureteric stones, and urinalysis showed glucosuria and pyouria. She was given antibiotics and analgesics and she was discharged. During the ensuing 48 hours and despite treatment her condition deteriorated rapidly and she developed clinical signs of septic shock.

The patient presented again and a computed tomography (CT) of the abdomen revealed an enlarged left kidney with extensive destruction of the parenchyma, along with collections of air within the collecting system and the parechyma (Figure 1). She was intubated and transferred to the ICU of our hospital where she was supported with intravenous hydration, antibiotics and inotropic agents. After her condition was stabilised she underwent a second CT scan of the abdomen that revealed an increased amount of intraparenchymal air (Figure 2a) and gas formation in the left perirenal space (Figure 2b). A radical left nephrectomy was performed immediately and after an uneventful post-operative period her condition improved. Cultures of blood and urine samples, collected on admission, grew E. coli.

Discussion

The excised kidney was hemmoragic, necrotic and purulent. The collecting system was filled with pus, that was cultured and grew also E. coli. Histology revealed extensive necrosis, microabscess formation and polymorphonuclear infiltration, findings suggesting emphysematous pyelonephritis. Emphysematous pyelonephritis (EPN) is a rare infection of the kidney, characterized by gas formation within the collecting system, the renal parenchyma, and the perirenal space. EPN is a life threatening condition affecting mainly diabetic female patients, especially those with urinary tract obstruction. The most common infecting organism is E. coli (70%), followed by K. pneumoniae (24%). The pathogenesis of the disease is characterized by acute necrosis of the renal parenchyma due to lowered immune defenses. The necrotic tissues in the presence of glucose-rich urine represent a substrate for fermentation and gas formation (1). The clinical picture of EPN is non-specific, and similar to that of uncomplicated acute pyelonephritis. Therefore, the diagnosis is always based on radiographic findings. Plain abdominal radiography allows easy detection of gas within or around the affected kidney. Yet, according to several reports (2), plain films have low sensitivity (33%) because it is difficult to differentiate between renal gas and air in the overlying intestinal loops. The typical US appearance of EPN is that of high-amplitude flat anterior margin echoes within the renal sinus or calyces, which are associated with distal shadowing containing low level echoes and reverberations (2). Nevertheless, US cannot differentiate easily between renal gas and renal calculi or calcifications. Characteristically, in a series of five patients with EPN shadowing from the calyces was interpreted as ureteric stones in three patients and as gas in two (2). CT is the best imaging modality for the diagnosis of EPN (2). Recently, two types of EPN were described based on the CT findings: Type I is characterized by parenchymal destruction, with either absence of fluid collections or presence of streaky or mottled-appearing gas. Type II is characterized by either gas in the collecting system or renal or perirenal fluid collections with bubbly gas (3). Classification of EPN to type I or II has prognostic significance since EPN type I has a higher mortality rate compared to type II (69% versus 18%) and a more fulminant course (3). Given the high mortality associated with this disorder even after aggressive medical therapy, nephrectomy is almost always indicated as soon as CT establishes the diagnosis of EPN (4).

Differential Diagnosis List

Final Diagnosis

Emphysematous pyelonephritis

URL:	https://www.eurorad.org/case/1358
DOI:	10.1594/EURORAD/CASE.1358
ISSN:	1563-4086