KEY FACTS
Terminology
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Hemorrhagic collection in perinephric spaces: Subcapsular, perirenal, anterior and posterior pararenal
Imaging
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Avascular solid or cystic masses in 1 or more perinephric spaces
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Echogenicity of blood changes over time
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Sonographic features vary over time
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Acute: Highly echogenic perinephric mass
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Subacute: Partial liquefaction, echogenic debris, retractile clot with thick septa
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Chronic: May be almost anechoic
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Useful to assess perfusion in compressed kidney
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Sometimes reveals etiologies such as pseudoaneurysm
Top Differential Diagnoses
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Lymphoma infiltration
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Cystic lymphangioma
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Perinephric abscess
Pathology
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Causes include trauma, renal biopsy, renal cyst or tumor rupture, anticoagulation, aneurysm rupture
Clinical Issues
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Treatment varies with etiology
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Hematoma without underlying significant pathology usually resolves spontaneously
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Flank pain, often severe, palpable mass, shock
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Diminished hematocrit may prompt evaluation
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Subcapsular hematoma may cause hypertension due to renin-angiotensin-aldosterone cascade (Page kidney)
Scanning Tips
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Look for underlying malignancy, which can often be cause of spontaneous perinephric hematoma
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Use power Doppler to show perinephric hematoma is avascular and to distinguish from adjacent renal cortex
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Perinephric fat in diabetic patients (often hypoechoic) may mimic perinephric hematoma; compare with contralateral side to demonstrate bilaterality
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When gain is too low, hypoechoic hematoma may be missed; when gain is too high, echogenic hematoma may be missed
