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

Abstract

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. Prospective controlled trial. 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. 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%). 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.