Ultrasound follow up: Is an undetected spontaneous expulsion of stone fragments a sign of extracorporeal shock wave treatment failure in kidney stones?

Introduction. After extracorporeal lithotripsy (SWL), a spontaneous expulsion of fragments is often reported. The aim of this study is to demonstrate the presence of a stone free status or the presence of clinically insignificant residual fragments (CIRFs, defined as “asymptomatic, noninfectious, ≤ 3 mm fragments”) in people with undetected spontaneous expulsion. Materials and methods. Between May and September 2017, we performed a total of 87 treatments. The device used was a Storz Medical Modulith® SLK. All the patients were treated in prone position to reduce respiratory movements and underwent sonography before and four to eight weeks after the treatment. An in line ultrasound targeting was possible with all the stones. People lost to follow up or with ureteral stones were excluded. Patients were divided in groups according to gender, previous treatments, stone diameter and position. Results. We enrolled 73 patients. 57 patients had a single stone and 16 multiple stones. A mean number of 3044 shock waves was administered with a maximum average energy of 0.68mj/mmq. At follow up, 41 patients (56.2%) were found stone free or with CIRFs. The association between undetected expulsion and the presence of CIRFs is considered to be not statistically significant (p = 0.89). Among patients with CIRFs, 25/41 didn’t report expulsion. Taking in account the groups our population was divided in, according to gender (p = 0.36), previous treatments (p = 0.44), stone diameter (p = 0.28) and stone position (p = 0.35), the association between undetected spontaneous expulsion and presence of CIRFs was never statistically significant. Conclusions. An undetected spontaneous expulsion of stone fragments could not be considered a sign of SWL treatment failure. The association between undetected expulsion and presence of CIRFs is never statistically significant if gender of the patients, previous treatments, stone diameter and stone position are considered.