Diagnostic Ultrasound - Abdomen and Pelvis

Renal Metastases
IMAGING
General Features
• Best diagnostic clue
○ Imaging findings are nonspecific
○ Typically multiple and small, bilateral, hypoenhancing
renal masses
○ More likely to be endophytic, compared to renal cell
carcinoma (RCC), which is more likely exophytic
○ Large exophytic metastases may be encountered
○ Perinephric infiltration from tumor extension or
hemorrhage may be seen (more common in melanoma)
○ Most patients have metastatic tumor at other locations
Ultrasonographic Findings
• Grayscale ultrasound
○ Usually small and round, may be wedge-shaped
○ Usually cortical; rarely disrupting renal contour or capsule
○ May be hypoechoic, hyperechoic, or sonographically
occult
○ Occasionally infiltrative
• Color Doppler
○ Mostly avascular or hypovascular, using low flow Doppler
settings
○ Melanoma metastasis can be hypervascular; may
simulate RCC
CT Findings
• Usually small, bilateral, and multifocal
• Iso- to hypodense on NECT, poorly enhancing
• Cystic/necrotic or hypervascular variants depending on
primary malignancy
• Widespread extrarenal metastases usually present
Nuclear Medicine Findings
• PET
○ Increased uptake in F-18-2-fluoro-2-deoxy-glucose (FDG)
scan, extrarenal lesions in majority
DIFFERENTIAL DIAGNOSIS
Primary Renal Neoplasms
• RCC: Solitary renal cortical mass, hypervascular, usually
exophytic, may be necrotic
• Transitional cell carcinoma: Infiltrative mass + obstruction
of collecting system
Renal Angiomyolipoma
• Majority are echogenic due to intratumoral fat content
• May also be multiple or bilateral
Renal Cyst
• Anechoic, lacking color flow, can be multiple
Renal Lymphoma or Leukemia
• Multifocal or infiltrative masses, ±perirenal masses or
lymphadenopathy
Renal Infection
• Focal pyelonephritis may mimic metastasis
• Clinical picture of infection is key for diagnosis
Renal Infarction
• Avascular, wedge-shaped renal lesion
PATHOLOGY
General Features
• Etiology
○ Dissemination of advanced primary malignancy;
hematogenous > direct spread
Microscopic Features
• Varies based on primary cancer
• Metastases are distinctly different from primary renal cell
cancers on cytological smears
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Usually asymptomatic; may have hematuria or
microhematuria (12-31%)
• Other signs/symptoms
○ Most found on imaging or at autopsy
○ Acute pain or hypotension from perinephric hemorrhage
Demographics
• Epidemiology
○ Most common malignant renal tumor at autopsy (7-13%
of autopsies),20% of patients dying of disseminated
malignancy
○ Lung cancer most common primary site followed by
breast, gastric, and melanoma
Natural History & Prognosis
• Prognosis very poor
• More common in patients with higher stage of nonrenal
malignancy
Treatment
• Chemotherapy or palliative treatment
• Nephrectomy if metastasis is small and isolated
DIAGNOSTIC CHECKLIST
Consider
• Multiple renal masses likely to be metastases in presence of
nonrenal primary cancer and widespread systemic
metastases
• Single renal mass in patient with nonrenal malignancy could
be metastasis or synchronous primary renal malignancy
○ Differentiation between the above can be made with CT
or US-guided percutaneous biopsy if this directly
influences treatment
SELECTED REFERENCES
1. Roy A et al: Common and uncommon bilateral adult renal masses. Cancer
Imaging. 12:205-11, 2012
2. Patel U et al: Synchronous renal masses in patients with a nonrenal
malignancy: incidence of metastasis to the kidney versus primary renal
neoplasia and differentiating features on CT. AJR Am J Roentgenol.
197(4):W680-6, 2011
Diagnoses: Urinary Tract
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