Diagnostic Ultrasound - Abdomen and Pelvis
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Diagnostic Ultrasound - Abdomen and Pelvis

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Emphysematous Pyelonephritis TERMINOLOGY Abbreviations • Emphysematous pyelonephritis (EPN) Definitions • Gas-forming upper urinary tract infection involving renal parenchyma &/or perinephric space IMAGING General Features • Location ○ Unilateral > bilateral (5-7% of cases) Ultrasonographic Findings • Grayscale ultrasound ○ Highly echogenic areas within renal sinus and parenchyma with "dirty" shadowing ○ Ring-down artifacts: Air bubbles trapped in fluid ○ Gas in perinephric space or perinephric collections may obscure kidney • Color Doppler ○ Twinkling artifact: May mimic stones Radiographic Findings • Radiography ○ Gas in parenchyma ± perinephric space CT Findings • 2 types of emphysematous pyelonephritis ○ Type I (33%): Parenchymal replacement by gas,± subcapsular or perinephric gas ○ Type II (66%): Renal or perirenal abscesses with gas, ± gas within renal pelvis • Intraparenchymal, intracaliceal, and intrapelvic gas • Gas may extend into subcapsular, perinephric, pararenal, contralateral retroperitoneal spaces MR Findings • T1WI, T2WI: Foci of gas are signal voids on all sequences • T2WI:Perinephric edema ± fluid collections Imaging Recommendations • Best imaging tool ○ CT is ideal to determine location and extent of renal and perirenal gas ○ Evaluation for psoas abscess and spinal osteomyelitis is essential DIFFERENTIAL DIAGNOSIS Renal Calculus • Discrete echogenic focus with sharp distal acoustic shadowing Nephrocalcinosis • Generalized increased echogenicity of renal pyramid ± shadowing Papillary Necrosis • Single or multiple cystic cavities in medullary pyramids continuous with calyces • Sloughed papillae: Echogenic, nonshadowing Emphysematous Pyelitis • Gas limited to renal collecting system and pelvis, not parenchyma • Usually less clinically serious than EPN Benign Gas in Renal Pelvis • May arise from recent interventions PATHOLOGY General Features • Etiology ○ Single or mixed organism(s) infection – Escherichia coli (68%), Klebsiella pneumoniae (9%) – Proteus mirabilis, Pseudomonas, Enterobacter, Candida, Ilostridia species ○ Risk factors – Recurrent or chronic UTIs – Immunocompromised: Diabetes mellitus (87-97%) – Ureteral obstruction (20-40%): Calculi, stenosis ○ Pathogenesis – Pyelonephritis → ischemia and low oxygen tension → anaerobe proliferation in anaerobic environment → CO2 production Gross Pathologic & Surgical Features • Suppurative necrotizing infection of renal parenchyma and perirenal tissue with multiple cortical abscesses CLINICAL ISSUES Presentation • Most common signs/symptoms ○ Extremely ill at presentation: Fever, flank pain, hyperglycemia, acidosis, dehydration, and electrolyte imbalance ○ Hypoalbuminemia and need for emergent hemodialysis are independent predictors of mortality Natural History & Prognosis • Complications: Generalized sepsis • Prognosis: Poor ○ Mortality: 66% with type I, 18% with type II Treatment • Antibiotic therapy; nephrectomy for type I ○ Conservative management fails in at least 1/3 of cases • CT-guided drainage procedures for type II SELECTED REFERENCES 1. Lu YC et al: Predictors of failure of conservative treatment among patients with emphysematous pyelonephritis. BMC Infect Dis. 14:418, 2014 2. Lin YC et al: Risk factors of renal failure and severe complications in patients with emphysematous pyelonephritis-a single-center 15-year experience. Am J Med Sci. 343(3):186-91, 2012 3. Chen KC et al: The role of emergency ultrasound for evaluating acute pyelonephritis in the ED. Am J Emerg Med. 29(7):721-4, 2011 4. Ubee SS et al: Emphysematous pyelonephritis. BJU Int. 107(9):1474-8, 2011 5. Grayson DE et al: Emphysematous infections of the abdomen and pelvis: a pictorial review. Radiographics. 22(3):543-61, 2002 Diagnoses: Urinary Tract 483

Emphysematous Pyelonephritis Diagnoses: Urinary Tract (Left) Abdominal radiograph shows a mottled gas pattern projecting over the expected location of the left renal fossa in a patient with emphysematous pyelonephritis. (Right) On grayscale US imagining, multiple punctate and highly echogenic foci of gas ſt are seen in a subcapsular collection compressing the lower pole of the right kidney in a different patient. These echogenic foci are nondependent (floating in fluid) and were seen to move with real-time imaging. (Left) Doppler US in the same patient shows color signal related to twinkling artifact associated with the gas bubbles st. To prevent confusion with true vascular flow, spectral tracings should be obtained. In this case, the waveform demonstrated noise (not shown), which verified that this area of color was artifactual and not true vascular flow. (Right) Axial NECT in the same patient confirms multiple foci of gas ſt in the subcapsular collection, which compresses the renal contour . (Left) CECT shows a markedly enlarged right kidney with a delayed and faint nephrogram compared to the contralateral side. Multiple foci of gas in the upper pole parenchyma confirm the diagnosis of emphysematous pyelonephritis. (Right) Dynamic renal scan images in the same patient show near absence of activity in the infected right kidney (patient is prone) with normal uptake and excretion on the left ſt. This study was performed as part of surgical planning for right nephrectomy. 484

Emphysematous Pyelonephritis<br />

Diagnoses: Urinary Tract<br />

(Left) Abdominal radiograph<br />

shows a mottled gas pattern<br />

projecting over the<br />

expected location of the left<br />

renal fossa in a patient with<br />

emphysematous<br />

pyelonephritis. (Right) On<br />

grayscale US imagining,<br />

multiple punctate <strong>and</strong> highly<br />

echogenic foci of gas ſt are<br />

seen in a subcapsular<br />

collection compressing the<br />

lower pole of the right kidney<br />

in a different patient.<br />

These echogenic foci are<br />

nondependent (floating in<br />

fluid) <strong>and</strong> were seen to move<br />

with real-time imaging.<br />

(Left) Doppler US in the same<br />

patient shows color signal<br />

related to twinkling artifact<br />

associated with the gas<br />

bubbles st. To prevent<br />

confusion with true vascular<br />

flow, spectral tracings should<br />

be obtained. In this case, the<br />

waveform demonstrated noise<br />

(not shown), which verified<br />

that this area of color was<br />

artifactual <strong>and</strong> not true<br />

vascular flow. (Right) Axial<br />

NECT in the same patient<br />

confirms multiple foci of gas<br />

ſt in the subcapsular<br />

collection, which compresses<br />

the renal contour .<br />

(Left) CECT shows a markedly<br />

enlarged right kidney with<br />

a delayed <strong>and</strong> faint<br />

nephrogram compared to the<br />

contralateral side. Multiple<br />

foci of gas in the upper pole<br />

parenchyma confirm the<br />

diagnosis of emphysematous<br />

pyelonephritis. (Right)<br />

Dynamic renal scan images in<br />

the same patient show near<br />

absence of activity in the<br />

infected right kidney <br />

(patient is prone) with normal<br />

uptake <strong>and</strong> excretion on the<br />

left ſt. This study was<br />

performed as part of surgical<br />

planning for right<br />

nephrectomy.<br />

484

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