ELECTROMAGNETIC SHOCK-WAVE LITHOTRIPSY OF GALLBLADDER STONES IN-VITRO- THE ROLE OF DIFFERENT STONE CHARACTERISTICS AND TREATMENT VARIABLES

From 40 sets of five human gallstones obtained at cholecystectomy, fou r stones were subjected to either 125/250 (maximum generator output) o r 250/500 (half maximum generator output) electromagnetic shock waves (treatments I/II and III/IV, respectively); the fifth stone was used f or computed tomography (CT) and chemical analysis. Overall, 130 (81%) of 160 stones fragmented, including 72 (45%) adequately (fragments les s-than-or-equal-to 5 mm). For the treatments I, II, III, and IV the ov erall fragmentation rates were 80%, 95%, 70%, and 80%, respectively. T he corresponding percentages of adequate fragmentation (less-than-or-e qual-to 5 mm) were 38%, 70%, 30%, and 42%, respectively. The best resu lts were thus obtained after application of 250 shock waves (maximum g enerator output; treatment II). Pure cholesterol stones (p < 0.01), st ones with a mean CT density less-than-or-equal-to HU (p < 0.001), and stones with a calcified rim (p < 0.05) fragmented significantly better , but adequate fragmentation (less-than-or-equal-to 5 mm) was signific antly determined by stone weight and diameter (p < 0.001), bilirubin c ontent (p < 0.02), and calcium content (p < 0.05). A weight > 500 mg a nd a diameter > 10 mm could be defined as stone characteristics with s ignificant negative predictors of adequate fragmentation. However, bec ause the experimental conditions in this in vitro study did not comple tely simulate clinical settings for various reasons, these observation s must be interpreted accordingly. High correlations between mean CT a ttenuation numbers (HU) and cholesterol (r = -0.87; p less-than-or-equ al-to 0.001) or calcium (r = 0.92; p less-than-or-equal-to 0.001) cont ent were found. Using a cutoff point of 110 HU, pure cholesterol (grea ter-than-or-equal-to 80% cholesterol) and noncholesterol stones could be discriminated by CT with an overall accuracy of 95%.