Diagnostic Ultrasound - Abdomen and Pelvis

Renal Vein Thrombosis
TERMINOLOGY
Abbreviations
• Renal vein thrombosis (RVT)
Definitions
• Clot formation in renal vein (RV)
IMAGING
General Features
• Best diagnostic clue
○ Echogenic material in RV with absence of flow on color
Doppler US
○ Reversal of diastolic flow on spectral Doppler tracing of
renal artery is indirect sonographic finding of RVT
• Location
○ Unilateral > bilateral
○ Left renal vein > right renal vein, probably because it is
longer
○ Possible inferior vena cava (IVC) thrombus extension
• Size
○ Kidney enlarged acutely in 75% cases
○ RV dilated acutely
○ May see shrunken, scarred kidney chronically
Ultrasonographic Findings
• Grayscale ultrasound
○ Acute thrombosis
– Renal enlargement
□ Venous congestion → edema → renal enlargement
□ Enlargement varies & depends on degree of RV
obstruction
– Altered parenchymal echogenicity (3 patterns)
□ Diffusely hypoechoic, no corticomedullary
differentiation
□ Diffusely heterogeneous (if extensive hemorrhage
and necrosis)
□ Linear echogenic "streaks" radiating from hilum
(thrombosed parenchymal veins)
– Renal vein distended (faintly echogenic material)
– IVC thrombus extension (uncommon)
○ Subacute thrombosis
– ↑ cortical echogenicity, ↑ corticomedullary contrast
(after 10-14 days)
– Reduced RV size, increased thrombus echogenicity
○ Chronic thrombosis
– Appearance depends on amount of renal damage,
degree of RV flow restoration
□ Normal grayscale appearance
□ ↑ parenchymal echogenicity
□ ↓ kidney size (scar)
• Pulsed Doppler
○ Altered renal artery spectral waveforms
– ↑ systolic pulsatility (narrow, sharp systolic peaks)
– Persistent retrograde diastolic flow
○ Focal ↑ flow velocity around thrombus if nonocclusive
• Color Doppler
○ Acute occlusive thrombus
– Absent RV blood flow
– May see "tram-track" (small flow channels around
thrombus)
○ Acute nonocclusive thrombus
– Thrombus "filling defect" in RV flow column
– May see aliasing from ↑ flow velocity around
thrombus
○ Subacute/chronic
– Variable restoration of flow, depending on degree of
lysis
– Possible collateral veins (hilar, capsularretroperitoneal,
renal-splenic)
Other Modality Findings
• CT
○ Noncontrast CT may show enlargement and high
attenuation of thrombosed vessel
○ Perinephric &/or perivascular edema
○ Delayed nephrogram compared to contralateral side
○ Filling defect at portal venous phase may be hard to
distinguish from flow artifacts
○ Delayed phase imaging (2-5 minutes) most sensitive for
venous thrombosis
• MR
○ Absence of flow voids in thrombosed vessel
○ Perivascular edema on T2WI
○ Direct visualization of clot on delayed post-contrast
images
Imaging Recommendations
• Best imaging tool
○ Color Doppler and spectral Doppler US for initial
diagnosis
○ CT/MR for comprehensive assessment, follow-up
• Protocol advice
○ Do not mistake splenic vein for left renal vein (LRV)
– Splenic vein anterior to superior mesenteric artery
– LRV posterior to superior mesenteric artery
○ Doppler angle (60° or less), pulse repetition frequency,
and gain must be appropriate for low velocity flow
DIFFERENTIAL DIAGNOSIS
Renal Vein Tumor Invasion
• Renal cell carcinoma is most common cause of renal vein
tumor invasion; Wilms and urothelial tumors less common
• RV distended by faintly echogenic tumor (looks like
thrombus)
• May see tumor vessels in RV with color Doppler
• Kidney may be infiltrated, enlarged
Renal Parenchymal Infiltration
• Diffusely enlarged, hypoechoic kidney, loss of
corticomedullary differentiation
• Parenchymal appearance identical to RVT but vein is patent
• Infiltrative processes involving kidney that can mimic RVT
include: Lymphoma,renal cell carcinoma, urothelial
carcinoma, and amyloid
Pyelonephritis
• Enlarged, hypoechoic kidney, loss of corticomedullary
differentiation
• Appearance identical to RVT, but RV patent
Diagnoses: Urinary Tract
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