Hounsfield units on computed tomography predict calcium stone subtype composition.

INTRODUCTION: Hounsfield unit (HU) determination of urinary stones on noncontrast computed tomography (NCCT) has been shown to predict stone composition. However, no in vivo studies have attempted to radiographically separate the various calcium stone compositions. We investigate the efficacy of HU measurement on NCCT to determine if it can differentiate the various calcium stone subtypes. PATIENTS AND METHODS: Of the 684 patients who had undergone ureteroscopy at our institution from 1/2003 to 10/2007, 100 were identified with a documented NCCT, a chemical stone analysis and a stone size >5 mm but <2 cm. RESULTS: Stone compositions were categorized as 100-80% calcium oxalate monohydrate (CaOMH) (n = 24), <80-60% CaOMH (n = 21), <60-50% CaOMH (n = 11) calcium oxalate dihydrate (CaODH) (n = 16), apatite (n = 9), brushite (n = 4), cystine (n = 2) and uric acid (n = 13). Mean HU were 879 +/- 230, 769 +/- 295, 717 +/- 304, and 517 +/- 203 for the 100-80% CaOMH, <80-60% CaOMH, <60-50% CaOMH and CaODH groups, respectively. The average HU for the apatite, brushite, cystine and uric acid groups were 844 +/- 346, 1,123 +/- 254, 550 +/- 74 and 338 +/- 145, respectively. The CaOMH groups together had a significantly higher HU than the CaODH group (p < 0.05) and a significantly lower HU than the brushite group (p < 0.05). CONCLUSIONS: HU measurement of urinary stones on NCCT may be used to separate some calcium stone subtypes, specifically CaOMH and CaODH. This information may be useful in counseling patients on treatment options for patients requiring intervention.

A comparison of the FREDDY and holmium lasers during ureteroscopic lithotripsy.

BACKGROUND AND OBJECTIVE: Two laser devices that are used today in endoscopic treatment of renal and ureteral calculi are the frequency-doubled double-pulse neodynium:YAG (FREDDY) and Holmium:YAG lasers. The mechanism of action of these lasers differs, thus conferring potentially different safety and efficacy profiles. The in vitro efficacy of these lasers in treating urinary stones has been explored, but to our knowledge no study compares the in vivo efficacy. The purpose of this study is to compare the stone-free and complication rates of the FREDDY and holmium lasers. STUDY DESIGN/MATERIALS AND METHODS: Subjects were included in the study (from January 2004 to September 2006) if they had adequate documentation of stone size and location, postoperative stone burden, and perioperative complications. Stone-free status was determined based on intraoperative findings and postoperative imaging. Complications included bleeding, ureteral perforation, any intraoperative event necessitating termination of the procedure, ureteral stricture, hydronephrosis, and admission to the hospital with a diagnosis related to the procedure. RESULTS: Sixty patients with adequate follow-up were identified. Thirty patients were treated with FREDDY and 30 patients with Holmium laser. Fisher's exact test was employed for statistical analysis. There was no significant difference in the average stone size between the FREDDY and Holmium groups, which were 6.7 mm and 6.1 mm, respectively. Stone-free rates in the FREDDY and Holmium groups were 76.7% and 93.3%, respectively, P = 0.149. The complication rates were 17.4% in the FREDDY group and 10% in the Holmium group, P = 0.667. CONCLUSION: The complication and stone-free rates did not significantly differ between the FREDDY and Holmium lasers, though there was a trend toward a higher stone-free rate and lower complication rate with the holmium laser. Holmium laser may be more effective than the FREDDY laser in fragmenting calcium oxalate monohydrate stones. The device and laser fiber costs were comparable.