ESWL-induced Perinephric Hematoma

Ultrasound image of the kidney shows a crescentic heterogeneous hypoechoic lesion in the perinephric space (arrows). The kidney is marked by the calipers. 

Axial unenhanced CT images confirm a thick left perinephric hematoma (stars) and several fragmented stones in the lower pole of the left kidney.

Facts

• ESWL (Extracorporeal Shock Wave Lithotrypsy) is a common and standard treatment for renal/proximal ureteric calculi in majority of patients
• Most common complication = microscopic hematuria
• Perinephric hematoma and infection (including pyelonephritis) can occur
• Incidence of hematoma varies depending on method of diagnosis. By US, incidence is about 0.1-0.6%. By CT/MRI, incidence rises to 20-25% of cases. 
• No clear correlation between number of shockwaves or intensity given and incidence of hematoma
• Most perinephric hematoma resolves spontaneously within 2 years and the renal function is preserved. They are mostly treated conservatively

Imaging: US and CT

• Crescent-shaped collection surrounding the affected kidney
• Hypoechoic on US, hyperattenuating on non-contrast CT and no enhancement after IV contrast
• Displacement or compression of adjacent renal parenchyma
• Differentiate from subcapsular hematoma by appearance and pressure effect to underlying kidney.
• "Page" kidney occurs when (usually) subcapsular hematoma causes chronic renal parenchymal compromise and then hypertension

Reference:
Labanaris AP, Kuhn R, Schott GE, Zugor V. Perirenal hematomas induced by extracorporeal shock wave lithotripsy (ESWL). Therapeutic management. TheScientificWorldJOURNAL 2007;7:1563-1566.