Aetna considers extracorporeal shock wave lithotripsy for the treatment of sialolithiasis (salivary stones) experimental and investigational because its effectiveness has not been established.

Sialolithiasis refers to non-cancerous stones (calcium-rich crystallized minerals known as salivary calculi or sialoliths) in a salivary gland or duct.  Most salivary stones are single; however multiple stones may be present.  There are three pairs of major salivary glands: (i) the parotid glands, (ii) the sublingual glands, and (iii) the submandibular glands.  In addition to these major glands, there are hundreds of minor salivary glands that are scattered throughout the mouth and throat.  The submandibular glands are most often affected by stones (about 80% of cases), followed by the parotid gland and duct.  Stones are rarely found in the sublingual gland.  The higher frequency of sialolithiasis in the submandibular gland is associated with several factors: the pH of saliva (alkaline in the submandibular gland, acidic in the parotid gland); the viscosity of saliva (more mucous in the submandibular gland); and the anatomy of the Wharton’s duct (the duct of the submandibular salivary gland opening into the mouth at the side of the frenum linguaean is an “uphill course”).

Although the exact cause of sialolithiasis remains unclear, some salivary stones may be related to dehydration, which increases the viscosity of the saliva; reduced food intake, which decreases the demand for saliva; or medications that lower the production of saliva, including certain anti-histamines, anti-hypertensives and anti-psychotics.  Some salivary stones may not produce any symptoms.  In other cases, a stone may partially or completely block the gland or its duct causing pain and swelling in the affected gland/duct, especially when eating.  While small salivary stones sometimes pass out of the duct on their own, larger stones usually remain in the gland until they are removed.  In general, stones within the distal salivary duct are easily removed by trans-oral ductotomy.  On the other hand, proximal stones are usually treated by excision of the salivary gland and its duct.  Another relatively new therapeutic option for the treatment of sialolithiasis is extracorporeal shock wave lithotripsy (ESWL), which utilizes ultrasound to break up the stones.  The broken fragments can then pass out along the duct.  Although there is some preliminary evidence that ESWL may be of clinical value in treating patients with salivary stones, its effectiveness has not been validated by prospective randomized controlled studies.

In an experimental study, Escudier and associates (2003) examined the results of ESWL in the management of salivary stones (38 parotid and 84 submandibular).  Complete success was achieved in 40 procedures (33%), 27 of 84 (32%) submandibular and 13 of 38 (34%) parotid calculi.  A further 43 patients (35%) were rendered asymptomatic although some stone debris remained in the duct (26 submandibular and 17 parotid).  Failure (retention of stone debris and continued symptoms) occurred in 39 patients (32%), 30 submandibular and 8 parotid glands.  The chance of failure increased with the size of the calculus and increasing duration of symptoms.  These researchers reported that ESWL provides a useful option for the management of salivary stones, especially those that are less than 7 mm in diameter.

In a consecutive patient series, Capaccio et al (2004) evaluated the validity of ESWL for the treatment of sialolithiasis in a large series of patients with a long-term follow-up (median period of 57 months).  A total of 322 symptomatic outpatients with solitary or multiple calculi in the submandibular (234 patients) or parotid (88 patients) gland underwent a complete ESWL treatment.  Results were classified into 3 groups: (i) successful result with complete ultrasonographic elimination of the stone after lithotripsy, (ii) successful result with residual ultrasonographic fragments that were less than 2 mm in diameter, and (iii) unsuccessful result with residual ultrasonographic fragments that were greater than 2 mm in diameter.  Complete elimination of the stone was achieved in 45% of patients.  On ultrasonography, residual fragments (less than 2 mm in diameter) were detected in 27.3% of patients, and persisting fragments greater than 2 mm in diameter were found in 27.7% of patients.  In 3.1% of patients, all with submandibular gland stones, sialoadenectomy was performed.  Recurrence of calculi in the treated gland was observed during a median follow-up period of 57 months in 4 patients with complete ultrasonographic clearance of the stone occurring 10 to 58 months after lithotripsy.  On multivariate analysis, the age of the patient, parotid site of the stone, stone diameter, number of therapeutic sessions, and number of shock waves were associated with favorable outcome.  These investigators concluded that this minimally invasive approach should be considered an efficient therapy for salivary calculi.

The results by Escudier et al (2003) as well as Capaccio et al (2004) were unimpressive.  Complete success (elimination of stones) was achieved in only 33% of patients in the former study and 45% of patients in the latter study.

Zenk and colleagues (2004) performed a retrospective review on effectiveness of ESWL in the treatment of submandibular stones (n = 191).  The period under review ranged from 8 to 13 years, with an average of 10.5 years.  In all, 35% of the subjects (n = 67) were either stone-free or asymptomatic from the residual stones.  Another 15% (n = 29) had a significant improvement in their symptoms and needed no additional treatment.  The remaining 50% (n = 95) had residual stones; they had no symptoms in the short review period, but have had symptoms since.  The therapeutic success was not influenced by the size of the stone (this appears to be contradictory to the findings of Escudier et al, 2003), but by its location within the gland.  Following treatment, no severe adverse events were identified.  The authors concluded that ESWL is a possible therapy for submandibular stones and when combined with other gland-preserving methods forms part of a multi-therapeutic approach that renders submandibulectomy unnecessary in the majority of cases.

Yoskovich (2003) stated that in patients with stones in proximity of the opening of the Wharton’s duct, the duct can be cannulated, dilated and the stones removed through a trans-oral approach.  The author also stated that for patients with deep intra-parenchymal stones or multiple stones, the glands should be excised; ultrasonic lithotripsy is rarely effective.

In a review on the management of salivary stones, Marchal and Dukguerov (2003) commented that, with external lithotripsy, stones are expected to evacuate spontaneously once fragmented.  Although success rates of 75% for the parotid gland and 40% for the submandibular gland have been reported with ESWL, any residual stone is an ideal nidus (a point or place at which something originates, accumulates, or develops, as the center around which salts of calcium, uric acid, or bile acid form calculi) for further calcification and recurrence of salivary stones.  These investigators also noted that external lithotripsy could cause significant damage to the salivary glands.  Moreover, in a review on management modalities of submandibular sialoliths, Baurmash (2004) stated that lithotripsy does not appear to be a viable routine method of management for submandibular salivary stones.

McGurk et al (2005) examined the results of a minimally invasive approach in the treatment of salivary calculi (323 submandibular stones and 132 parotid stones).  Patients were treated using ESWL, fluoroscopically guided basket retrieval or intra-oral stone removal under general anesthesia.  The techniques were used either alone or in combination.  Exclusion criteria for ESWL include pregnancy, stones not readily identifiable by ultrasonography, patients with blood dyscrasias or hemostatic abnormalities, and individuals who have undergone stapedectomy or ossicular repair.  Extracorporeal shock wave lithotripsy resulted in complete success (stone-free and symptom-free) in 87 (39.4%) of 221 patients [84 (38.5%) of 218 primary and all of 3 secondary procedures; 43 (32.8%) of 131 submandibular, 44 (48.9 %) of 90 parotid].  Basket retrieval cured 124 (74.7%) of 166 patients (103 of 136 primary and 21 of 30 secondary procedures; 80 of 109 submandibular, 44 of 57 parotid).  Intra-oral surgical removal was successful in a further 137 (95.8%) of 143 patients with submandibular stones (99 of 101 primary, 36 of 38 secondary and 2 of 4 tertiary procedures).  The overall success rate for the three techniques was 348 (76.5%) of 455.  It should be noted that the ESWL achieved complete success only in 39.4 % of patients.  The authors also noted that earlier studies reported presence of residual fragments in 54 to 67% of patients who had undergone ESWL for salivary calculi.  These investigators claimed that minimally invasive techniques such as ESWL for the management of patients with sialolithiasis are still at an early stage of development.

While the results of recent reports are encouraging, further investigation (especially prospective randomized controlled studies) is needed to ascertain the effectiveness of extracorporeal shock wave lithotripsy in the treatment of salivary stones.