Introduction
Laser Types and Mechanism of Action
Several lasers have been studied and utilized in salivary stone lithotripsy. Zenk et al. have described in detail the development of laser stone fragmentation, including their research into stone fragmentation and duct wall effects of five different laser systems. Presently, the Holmium:YAG laser is the predominant system in use. Although some authors report a photoacoustic or shockwave mechanism of action, due to creation of a gas bubble and subsequent cavitation collapse, the mechanism of this laser is photothermal, resulting in stone vaporization.
Schrötzlmair et al. measured the outcome of in vitro stone fragmentation of harvested submandibular stones, subjected to Ho:YAG laser settings of 0.5, 1.0, and 1.5 J per pulse, using a 200 µm fiber. They studied a variety of physical and radiologic parameters of the stones, including computed tomography (CT) stone density, but did not find any correlation with measured stone parameters.
Outcome Data
Numerous papers have described outcomes of salivary stone fragmentation with the Holmium:YAG laser. Martellucci et al. described 16 patients with submandibular stones ranging between 5 and 8 mm in diameter. The stone location was not specified. All patients had a successful fragmentation. Three patients had residual symptoms; two were found to have retained stone fragments, which were removed at a subsequent procedure; and one patient had a stricture at the laser site, which was successfully dilated.
There are case reports describing laser fragmentation and endoscopic removal of large submandibular stones, notably by Sun et al., who successfully removed multiple large stones measuring up to 13 mm from the mid-ductal region of the submandibular duct, in a procedure exceeding 4 h in duration. A letter to the editor regarding this paper, by Sahin-Yilmaz and Oysu, described their experience in attempting laser fragmentation of a 7 mm stone in the parotid duct in a patient who had refused a transfacial procedure. The procedure was terminated after a 2 h attempt at laser fragmentation, and subsequent investigations identified a residual 4 mm stone. A second attempt at endoscopy found a dense stricture that could not be sufficiently dilated to access the remaining stone.
Sionis et al., reported on a series of patients undergoing sialendoscopy, including 15 patients who underwent Ho:YAG lithotripsy. There were eight submandibular and seven parotid patients, with stone sizes ranging from 4–15 mm. All stones were successfully fragmented and removed, except for one 15 mm stone in the submandibular gland, which underwent gland excision. One parotid patient had an intractable stenosis requiring parotidectomy.
Carta et al., described 16/21 cases that were successfully treated with a single laser procedure; 3/21 cases subsequently underwent gland excision, including 1/9 parotid stone patients, due to a parotid ductal stricture.
Capaccio et al. have published a detailed study of the range of options for salivary lithotripsy, including extracorporeal and intracorporeal options. They suggest that stones <7–10 mm are most suited to this technique. They comment that thermal ductal injury is a risk, and note that the procedure can be time consuming, is associated with a learning curve, and that success is inversely proportional to stone size.
The Ho:YAG laser is the predominant laser in use, based on relatively wide availability, due to the utility for other surgical services such as urology. However, there are other lasers also in use, as described in the literature.
Durbec et al., described the use of the Thulium:YAG laser in a review including 63 patients who were treated with this laser. A total of 78% were symptom free after a mean follow-up of 18 months. Complete fragmentation was achieved in 51/63 patients, with no instances of ductal stenosis or other serious complications.
Laser Stone Fragmentation Indications
Laser stone fragmentation is useful in a limited number of salivary stones. Laser fragmentation carries a risk of duct wall injury and resultant stenosis, which in the parotid duct can result in intractable obstruction, requiring gland excision for resolution of symptoms. In the Sionis et al. and Carta et al. papers, this complication occurred in 1/7 and 1/9 parotid laser stone procedures, respectively. The risk of incomplete stone removal, requirement for multiple procedures, and procedure duration needs to be weighed against the risks and outcomes of combined or open procedures.
In view of the limitations of laser stone fragmentation, it is preferable to remove a salivary stone intact wherever possible. For submandibular stones, except for small floating stones that can be removed intact with a basket, most stones are accessible through a transoral or combined endoscopic/transoral approach. For posterior hilar stones, or intraparenchymal stones, a few authors have reported very large case series with a high success rate of successful transoral removal (Capaccio et al. and Schapher et al. ). All of the stones removed in these two case series were palpable preoperatively. This approach is challenging, as adequate exposure of the stone can be difficult to achieve in some patients. For nonpalpable stones, the options are limited to endoscopic intraductal fragmentation, extracorporeal lithotripsy, or gland excision.
Small floating (L1 LSD Classification, Marchal et al. ) stones can commonly be extracted intact; however, they can be trapped behind a stenosis. In , a 53-year-old woman with recurrent left submandibular gland obstruction was found to have a 3 mm stone in the proximal third of the duct ( Fig. 22.1 ). The laser is a useful tool in this situation.
