Diagnostic Ultrasound - Abdomen and Pelvis

Solid Renal Mass
968
Differential Diagnoses: Kidney
DIFFERENTIAL DIAGNOSIS
Common
• Renal Cell Carcinoma
• Renal Angiomyolipoma
• Upper Tract Urothelial Cancer
• Renal Pseudotumor
○ Column of Bertin
○ Dromedary Hump
○ Focal Hypertrophy
• Focal Pyelonephritis
• Horseshoe Kidney
• Crossed Fused Ectopia
• Renal Lymphoma
• Renal Leukemia and Myeloma
• Renal Metastases
• Other Renal Tumors
○ e.g., Oncocytoma
• Wilms Tumor
Less Common
• Xanthogranulomatous Pyelonephritis (XGP)
• Renal Sinus/Replacement Lipomatosis
• Renal Tuberculosis
• Renal Papillary Necrosis
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
• Major role of grayscale US is to characterize simple cysts
• For noncystic lesions, evaluate margin and echogenicity
• Highly echogenic shadowing lesions suggestive of fat
○ Also consider calcification or gas
• Solid lesions should be carefully evaluated for intrinsic
blood flow
• Use color or power Doppler for internal vascular flow
○ Color flow in solid areas, septa, nodules, or debris
○ Presence of internal flow highly suspicious for
malignancy
• CECT or CEMR usually next line for solid renal mass
characterization and staging
• Contrast-enhanced ultrasound increases sensitivity for
tumor perfusion
○ Complementary to enhanced CT or MR
○ Substitute for CT and MR when patient cannot receive
iodinated or gadolinium-based contrast
• Look for other lesions ipsilateral and contralateral
• Beware of pseudotumors
○ Pseudotumors are isoechoic to normal parenchyma and
have normal kidney architecture
○ Pseudotumors are identical to normal kidney on CT and
MR before and after contrast
• Look for signs of malignancy
○ Renal vein invasion, inferior vena cava (IVC) tumor
thrombosis, regional lymphadenopathy, and liver
metastasis
• Interpret findings with clinical information, e.g., fever,
trauma, known malignancy
• Consider risk factors, e.g., dialysis, von Hippel-Lindau
disease
Helpful Clues for Common Diagnoses
• Renal Cell Carcinoma
○ Most common primary renal malignancy
○ Variable grayscale US appearances: Solid, heterogeneous
cystic and solid or predominantly cystic
○ Hyperechoic (48%), isoechoic (42%), hypoechoic (10%)
○ Large tumors tend to be hypoechoic, exophytic with
anechoic necrotic areas
○ Hypoechoic pseudocapsule
○ Smaller tumors tend to be hyperechoic, overlapping with
angiomyolipoma (which shadow)
○ May contain dystrophic coarse calcification
○ Color Doppler: Peripheral, intratumoral vascularity
○ Associated with renal vein thrombosis (23%) and IVC
tumor extension (7%)
• Renal Angiomyolipoma
○ Benign tumor containing fat, smooth muscle and
dysmorphic vascular tissue
○ Sporadic when single
○ Multiple in tuberous sclerosis complex
○ Echogenic lesion but can be variable depending upon
relative amounts of fat and soft tissue
○ Small lesions (< 3 cm ) are well marginated and
hyperechoic
○ Acoustic shadowing in 21-33%; distinguishing feature
from RCC
○ Internal vascularity and aneurysms
○ May be complicated by hemorrhage, which confounds
imaging diagnosis on US, CT, and MR
○ Confirm fat with CT or MR
• Upper Tract Urothelial Cancer
○ Hypovascular soft tissue lesion centered in renal pelvis
○ Associated with hydronephrosis
○ Infiltrative, preserving renal contour when large
○ Synchronous and metachronous bladder and upper tract
tumors
• Renal Pseudotumor
○ Column of Bertin
– Hypertrophied band of cortical tissue that separates
pyramids of renal medulla
– Isoechoic mass like lesion continuous with renal cortex
– Normal external renal outline but indent renal sinus
fat
– Normal vascularity on Doppler
○ Dromedary Hump
– Focal bulge in lateral border of left kidney mid-pole
– Similar to rest of kidney
– Calyces extend into hump with normal vascular supply
○ Focal Hypertrophy
– Hypertrophied kidney next to scar
– Similar appearance to rest of normal kidney
• Focal Pyelonephritis
○ Loss of corticomedullary differentiation, enlarged kidney
○ Hypoechoic round or wedge-shaped lesions
○ May have increased echogenicity due to hemorrhage
○ Other features of inflammation: Renal enlargement,
urothelial thickening of renal pelvis
○ Later liquefaction and abscess formation
○ Decreased color Doppler flow
○ Clinical picture of infection