Factors influencing the outcome of extracorporeal shock wave lithotripsy in the management of salivary calculi

Objectives/Hypothesis: To identify the factors that affect outcome (stone clearance, partial clearance without symptoms, and residual stone with symptoms unchanged) of extracorporeal shock wave lithotripsy (ESWL). To develop and validate a predictive model for outcome of treatment. Study Design: Prospective controlled trial. Methods: There were 142 salivary calculi (78 submandibular, 64 parotid) entered into a prospective clinical trial of ESWL. The results were analyzed and a predictive model generated, which was validated using a second group of patients treated by the same technique. Results: ESWL achieved complete success (stone and symptom free) in 67 (47.15%) of cases (submandibular 28/78, 35.9%; parotid 39/64, 60.9%). Partial success (residual stone and symptom free) was obtained in a further 49 (34.5%) (submandibular 29/78, 37.2%; parotid 20/64, 31.3%). Failure occurred in 26 (18.3%) of cases (submandibular 21/78, 26.9%; parotid 5/64, 7.8%). Conclusions: ESWL can eradicate salivary calculi but its effectiveness is dependant mainly on size of the stone. Using a regression analysis model stone clearance can be reliably predicted based on stone size. A less important factor is the radiodensity of the stone, whereas a greater proportion of parotid calculi are eliminated by ESWL than submandibular calculi.