Greater Stone Density Predicts SWL Failure

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Eur Urol. 2007;51:1688-1694

 

High renal-stone density and elevated BMI decrease the likelihood of stone disintegration with shock wave lithotripsy (SWL), Egyptian researchers conclude.

 

Ahmed R. El-Nahas, MD, and his colleagues at the Urology and NephrologyCenter at MansouraUniversity studied 120 patients with a solitary renal stone 0.5-2.5 cm in length. The patients had a mean age of 42.6 years and included 71 men and 49 women. Stone density was measured by high-resolution non-contrast CT. SWL was performed using an electromagnetic lithotripter. Dr. El-Nahas' group observed failure to disintegrate (defined as no stone fragmentation after three sessions) in 15 patients (12.5%). Ten of these patients underwent percutaneous nephrolithotomy. Retrograde ureteroscopy and laser disintegration were performed on the other five patients. If the renal stones were partially disintegrated after three sessions, patients underwent additional SWL treatments.

 

Stone density greater than 1000 Hounsfield units was associated with an eight times increased likelihood of failure to disintegrate. The mean BMI was 32.5 kg/m2 for 15 patients in the failure-to-disintegrate group compared with 28.1 kg/m2 in the 105 successful cases. Each1 kg/m2 increase in BMI was associated with a 12% in-creased likelihood of failure to disintegrate. In addition, obese patients (BMI 30 kg/m2 or higher) were 3.4 times more likely than non-obese patients to require more than three SWL sessions to achieve stone fragmentation.

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