Pathogenesis and Shock Wave Rate Dependence of Intrarenal Injury from Extracorporeal Lithotripsy

The morphologic pathomechanism of the response of the most vulnerable intrarenal structures and its dependence on the application form of extracorporeal shock wave lithotripsy (SWL) should be investigated. In a first series, 500, 1000, or 2000 shock waves from the Dornier HM3 SG40 were applied to the right kidneys of 54 Wistar rats. After 24 hours or 7 or 35 days, histologic examination and scanning electron microscopy (SEM) were done. In a second series, the administration of single (SS) and double (DS) shock wave forms (within 70 msec) were compared for 600 and 1200 shock waves in 40 rats. Cavitation bubbles in the arcuate veins seemed to cause rupture of these vessels as an accidental focal event, followed by intrarenal hematoma at the corticomedullary junction. These acute intrarenal hematomas were the most important damage. Organization led to intrarenal fibrosis in long-term specimens. Administration of DS waves enhanced the percentage of intrarenal hematoma (600 shock waves: DS 4.1 ± 0.8%, SS 1.9 ± 0.4%; P < 0.02; 1200 shock waves: DS 7.8 ± 0.9%, SS 5.6 ± 0.5%;P < 0.02). Functionally, the tubular enzyme marker N-acetyl-β-glucosaminidase increased in the 1200 shock wave group under DS compared with SS (DS 17.61 ± 4.1 U/L, SS 9.8 ± 3.2 U/L; P < 0.04). In long-term follow-up of 1200 shock waves, DS caused more fibrosis than SS (4.2 ± 0.41% v 2.6 ± 0.6%; P < 0.02). Thus, the development of the smaller focal area would be helpful to spare the tissues surrounding calculi. In high-risk patients, double-shot administration has to be used carefully.