Treatment of salivary obstructions

For the North American continent, the extracorporeal shockwave lithotriptor designed for salivary glands is not yet available for use in treating patients. The reasons are multiple, but mainly hinge on the costs associated with the Food and Drug Administration (FDA) approval application. The process must be initiated by an applicant company. In the case of lithotriptors, the company must weigh recouping the costs of FDA filing against the number of anticipated customers for an instrument approaching half a million dollars in cost. It is uncertain when such a lithotriptor device will become available. Also, renal lithotriptors are not appropriate for use on salivary stones and can lead to major complications. Until salivary lithotriptors become available, physicians in North America will continue to see patients with obstructive salivary duct stones; they will need to proceed with treatments without extracorporeal shockwave lithotripsy (ESWL).

Standard North American treatment for salivary duct and gland obstructions remains the sialadenectomy of either the parotid or submandibular glands. On removal of the gland and the duct containing the stone, no further obstructive symptoms will occur; however, the gland’s function is lost to the patient and can affect well-being. In a young patient, the other glands may compensate for the loss. With age, however, the remaining salivary glands may fall into decline for any one of many reasons. The missing excised gland could have made a significant percentage contribution to function and rendered the patient asymptomatic. Additionally, there is always the possibility of a gland resection complication, especially of nerve deficiencies.

In patients with salivary stones and strictures, without access to ESWL, the salivary endoscope with endoscopic instruments is the major tool for accomplishing a minimally-invasive, gland-preserving procedure. Without a lithotriptor, endoscope use becomes expanded to bridge the difference between a large stone, preferably treated with ESWL, and a stone requiring open resection. By expanding endoscope use, new and challenging situations arise requiring skill at manipulation of the endoscopic instrumentation. As a stone increases in size, it changes in character. A small stone will float within the duct and can be grasped with forceps or wire basket for removal. As the stone enlarges, it begins to dilate the duct and thin the duct wall. The inflammatory nature of the stone, the sequestered saliva, the stone pressure on the mucosa, and the bacterial challenges cause the duct lining to change. A normally smooth duct becomes waffled and may even form granulation tissue or polyps. The duct is expanded and the periphery of the stone is quite distant from the duct axis, which has implications for visualization during endoscopy. A thick adhesive stone “rind” may form at the interface between the stone and the duct mucosa. Multiple stones in a row may be present. The sialendoscopic physician’s skills must be used to address all of these issues, which would otherwise be mastered through the use of ESWL. For these reasons, there are differences in the stone treatment algorithms used by physicians who have access to ESWL and those who do not.

Parotid gland stones

For parotid stones ( Fig. 1 ) in the mid to proximal duct, sized 2.0 mm or smaller, removal by endoscopic forceps or basket is usually possible. If the stone is between 2.0 and 8.0 mm, endoscopic holmium laser lithotripsy with a 200 μm (or smaller) laser fiber followed by instrument removal is used, sometimes with a papillotomy. C-arm fluoroscopy with balloon dilation of the duct, followed by wire basket extraction, can also be used on these stones. For stones between 8.0 and 12.0 mm, a similar strategy is used as for the 2.0 to 8.0 mm group, recognizing that a progression to a staged endoscopic or an endoscopic-open approach will probably be needed.

Algorithm: parotid stones.

For sialendoscopic removal of very large stones solely by endoscopic means, without external incisions, several steps are required. The challenge is that a good portion of the stone may lie outside of the duct axis and field of view.

The laser is first used to drill tunnels into and through the central parts of the stone. This achieves a decompression of the gland. It also begins the fragmentation process. To increase the lithoclastic laser shockwave, the laser power can be temporarily increased to produce greater fracturing.

Next, more peripheral tunnels are created. As the peripheral tunnels are created, cracks in the stone appear and the stone starts collapsing toward its center. A wire basket and forceps are used intermittently to retrieve fragments. The laser process continues.

When the greater portion of the stone has been removed, a stone “rind” usually adheres to the duct wall. By maneuvering the endoscope and using external digital compression, the endoscope or laser fiber can be used to dissect and separate the stone from the duct wall. The loosened rind pieces can then be fragmented with the laser. Mini-forceps are used only to retrieve fragments; they are not strong enough to crush stones.

The duct wall of the parotid is stretched by the stone, and after stone removal there is a combination of edema, de-epithelialization, redundant mucosa, and laser damaged areas. The inside of the duct needs time to heal properly and re-epithelialize. The duct inevitably scars and becomes stenosed after such trauma. For this reason, it is of paramount importance to use a stent, sometimes for up to 4 weeks. Usually, a 4F hollow stent is used. The stent must be placed into the empty “socket” where the stone was once positioned. A guidewire is placed into the socket through the endoscope under direct vision. Measurement of the endoscope before and after its withdrawal allows for precise stent length determination and placement depth. The stent is placed over the guidewire, and then the guidewire is slowly withdrawn. It is sewn into position with two 5-0 silk sutures through the stent.

If, during the course of endoscopic removal, the stone rind is seen to be too adherent to dislodge and remove, then further endoscopic work becomes fruitless. An Endoscopic-Open or Endoscopic-Staged approach may be chosen instead. If a staged procedure is chosen, fractures in the stone decompress the salivary pressure and make the gland temporarily asymptomatic between stages.

For stones in the secondary, tertiary, and quaternary ducts, the endoscope and laser together can usually remove them. If the stone is large and expands the thin ducts, tissue-expander-like, into the parenchyma (ie, “intraparenchymal stone”), then an endoscopic-open preauricular approach can be selected. The Endoscopic-Open approach only raises a parotid flap and dissects directly down to the stone to remove it. If the gland drainage-basin proximal to the duct obstruction is heavily diseased with ectasias or multiple stenoses, then the Endoscopic-Open procedure should be expanded to an Endoscopic Segmental-Open approach whereby the wedge-shaped diseased gland tissue is also resected.