Diagnostic Ultrasound - Abdomen and Pelvis

Pyonephrosis
TERMINOLOGY
Definitions
• Obstructed renal collecting system containing pus or
infected urine
IMAGING
General Features
• Best diagnostic clue
○ Presence of mobile debris and layering of low-amplitude
echoes within dilated collecting system
Ultrasonographic Findings
• Grayscale ultrasound
○ Hydronephrosis, ±hydroureter, with internal debris
○ Most consistent finding: Low-level mobile echoes
○ Echogenic pus layering in dependent portion of
collecting system
○ Associated stone or gas sometimes seen
○ Urothelial thickening of renal pelvis or ureter
• Color Doppler
○ Resistive indices may be elevated
CT Findings
• Dilated collecting system containing intermediate- or highdensity
material
• Enlarged kidney with perinephric inflammatory changes
• Delayed nephrogram on affected side
• Gas or perinephric abscess may also be seen
DIFFERENTIAL DIAGNOSIS
Sterile Hydronephrosis
• Anechoic dilated collecting system, no dependent internal
echoes
Urothelial Carcinoma
• Solid tumor with vascularity within dilated collecting system
• Note that mucinous tumors may precisely mimic
appearance of pyonephrosis
• Longstanding hydronephrosis or pyonephrosis also
predisposes to squamous tumors
Complex Renal Cyst
• Echoes/solid component/septum within cyst
• No communication with renal pelvis or adjacent calyces
PATHOLOGY
General Features
• Etiology
○ Chronic > acute ureteral obstruction
– Calculus, congenital ureteropelvic junction
obstruction, or duplicated collecting system in young
adult
– Malignant ureteral stricture or other mechanical
obstruction in elderly
○ Stagnant urine becomes infected, filled with white blood
cells, bacteria, debris, and pus
– Ascending urinary tract infection
– Blood-borne bacterial pathogen
• Associated abnormalities
○ Complications: Renal abscess, perinephric abscess,
xanthogranulomatous pyelonephritis, fistula to
duodenum, colon, or pleura
Microscopic Features
• Purulent exudate composed of sloughed urothelium and
inflammatory cells from early formation of microabscesses
and necrotizing papillitis
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Fever, chills, flank pain
• Other signs/symptoms
○ Pyuria, leukocytosis, bacteriuria
Demographics
• Epidemiology
○ Most common organism: E. Coli
Natural History & Prognosis
• Progress to bacteremia or septic shock leads to 25-50%
mortality
• Delay in diagnosis and treatment leads to irreversible renal
parenchymal damage and renal failure
• Diabetes is a risk factor for worse clinical outcomes
• Nuclear medicine scans can be used to assess residual
function after acute illness is treated
Treatment
• Early diagnosis and drainage are crucial to prevent
bacteremia and septic shock
• Percutaneous nephrostomy is typical therapy
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
• May be indistinguishable from noninfected hydronephrosis
○ Proceed to percutaneous nephrostomy for urine
microscopy and culture if patient is clinically septic
SELECTED REFERENCES
1. Das CJ et al: Multimodality imaging of renal inflammatory lesions. World J
Radiol. 6(11):865-73, 2014
2. Kim SH et al: Serious acute pyelonephritis: a predictive score for evaluation
of deterioration of treatment based on clinical and radiologic findings using
CT. Acta Radiol. 53(2):233-8, 2012
3. Li AC et al: Emergent percutaneous nephrostomy for the diagnosis and
management of pyonephrosis. Semin Intervent Radiol. 29(3):218-25, 2012
4. Browne RF et al: Imaging of urinary tract infection in the adult. Eur Radiol. 14
Suppl 3:E168-83, 2004
5. Paterson A: Urinary tract infection: an update on imaging strategies. Eur
Radiol. 14 Suppl 4:L89-100, 2004
6. Wang IK et al: The use of ultrasonography in evaluating adults with febrile
urinary tract infection. Ren Fail. 25(6):981-7, 2003
Diagnoses: Urinary Tract
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