Introduction
Salivary gland obstruction accounts for about 50% of all benign salivary gland diseases. Sialolithiasis is one of the most frequent causes of inflammatory changes within the large salivary glands. Some salivary stones are expulsed with the saliva through the natural anatomic orifices and remain asymptomatic. The incidence of symptomatic stones requiring therapy amounts to 27.5–59 cases per million inhabitants.
In a large group of patients and in the literature, submandibular stones showed no statistical difference with respect to gender and is mostly diagnosed between the third and fourth decade of life, significantly about 10 years earlier than in parotid stones. But they can also already appear under the age of 20.
To understand the meaning of transoral endoscopy-assisted techniques, the most important feature is the location of stone formation within the duct system. Stones are 80% in the submandibular gland, 20% in the parotid gland, and infrequently in the sublingual or minor salivary glands. Considering the submandibular gland, 9% of the stones form in the intraparenchymal duct system, 53% within the hilum area, and 37% in the distal duct system. If one just differentiates between intraglandular parenchymal and extraglandular stones, one will find only 10% of the concrements localized intraglandularly. This is an important fact influencing the thoughts of a possible gland-preserving treatment.
Scintigraphic findings indicate that after removal of an obstruction, the glands can return to normal function; nonetheless, surgical removal of the gland is paradoxically still recommended. Based on available literature, the therapy of chronic (obstructive) sialadenitis of the submandibular glands has to be approached in a new context. Modern treatment is based on different approaches for submandibular gland preservation.
The first diagnosis of sialolithiasis or stenosis with a painful, swollen gland should initially be treated with secretory stimulants and massage of the affected gland. Dilation of the duct orifice, the narrowest part of the duct, can provide extensive relief of symptoms, including stone expulsion in cases of small stones. These conservative measures may lead to a remission of symptoms or stones in 13% of submandibular gland stones.
Many of the stones in Wharton’s duct can be directly and best visualized through sialendoscopy, which has therefore gained importance and has widely developed as a routine diagnostic tool. The technical advantages and improvements in new endoscopes with respect to size, optical, and material features have consequently led to a widened spectrum of indication for diagnostic and interventional sialendoscopy.
Interventional sialoscopy in cases of stones within the submandibular duct system is very successful for small and mobile stones. If concrements are impacted within the tissue, it might be possible to fragment or mobilize them and extract the fragments. Whether stones can be removed by endoscopic means is often decided during the diagnostic and therapeutic sialendoscopy.
Sialendoscopy is a basis for the decision of further therapy, including combined approaches. Sialendoscopy has been proven to be a safe procedure and it has been well tolerated. A low rate of complications (0.9%) is reported. With interventional sialendoscopy and sialendoscopic-assisted transoral combined approaches, extracorporeal and intracorporeal lithotripsy in submandibular stones are less important, or reserved for special conditions.
Clinical Algorithm for Endoscopic-Assisted Transoral Approach
Patients presenting with the typical history of recurrent and sometimes painful periprandial swelling of the submandibular gland are highly suspected to suffer from obstructive disease caused by a salivary stone located within Wharton’s duct or the intraparenchymal duct system. Following careful clinical examination, including gland massage, checking the salivary flow of the affected gland, and bimanual palpation of gland and duct system, imaging is indicated.
From the authors’ expertise in ultrasound, the 7.5 MHz probe is an ideal imaging choice for diagnosing salivary stones within the submandibular gland ( Figs. 18.1 , 18.2 ). When combining this method with stimulation of the gland by vitamin C, sensitivity and specificity will rise. Depending on the experience and available equipment, a computed tomography (CT) or magnetic resonance imaging (MRI) is also possible, although CT has the disadvantage of radiation exposure and MRI is more expensive.
Having diagnosed a salivary stone and failed conservative measures, the first step is a diagnostic endoscopy of Wharton’s duct combined with interventional measures, including basket extraction, mobilization, and, if possible, fragmentation and extraction of fragments.
In cases when the stone is too large in size and impacted within the duct, a sialendoscopic-assisted or combined transoral stone removal is the next indicated procedure. This is possible whenever the stone is visible during endoscopy within the course of Wharton’s duct up to the hilum of the gland and first order ducts. Even if the stone is smaller and not bimanually palpable within the gland hilum but visible, the indication for this procedure remains as the next step. For intraparenchymal stones, other options such as extracorporeal shock wave lithotripsy (ESWL) for smaller stones, and surgical removal of the gland for multiple and larger non-visible stones would follow.
Operative Procedures and Technique
General Considerations
The transoral excision of salivary stones using a simple incision of the orifice at the distal part of Wharton’s duct is, in most cases, uncomplicated. Also the transoral approach for the removal of salivary concrements in the first two distal anatomic sections of the duct is not too challenging. However, sialoliths lodged in the posterior third of the duct system, in the hilum or still further within the glandular parenchyma, present a problem. Stone removal proximal to the 1st molar or in the hilum of the submandibular gland endangers the lingual nerve. Various techniques of sialodochotomy of the submandibular duct have been described in the literature, while a major point of concern has always been the risk of injury to the lingual nerve that courses in close proximity to Wharton’s duct.
Therefore, the authors would recommend a technique in the beginning that involves the total longitudinal slitting of the duct from the ostium to the hilum with routine exposure of the lingual nerve and incision of the gland at the hilum to assist stone extirpation. This is the best way to initiate the technique leading to preservation of gland function in conjunction with a low level of risk and discomfort for the patient. The anatomy especially of the lingual nerve is clearly represented and therefore risk of injury is low. The duct thus provides the surgeon with an anatomic landmark as a guide. The lingual nerve, which crosses below the duct from lateral to medial, can thus be dissected without problem in a well-defined surgical field of view. The dissection can be extended and even the hilar part of the submandibular gland is exposed together with the edge of the mylohyoid muscle indicating the posterior border of the floor of the mouth.
A slightly different approach is not to incise directly at the ostium but to dissect the duct close to the ostium behind and then follow the duct below the mucosa without incision up to the hilum in combination with dissection of the lingual nerve. The incision of the duct system can then be made directly in front of the visible stone or guided by the endoscope at the tip of the instrument near the stone.
For experienced surgeons, a direct preparation through the floor of the mouth to the hilum of the gland led by the translucent light at the tip of the endoscope in front of the visible stone is possible, causing less incisional length. For this arrangement, particular attention and respect is necessary, in order not to harm the lingual nerve, which could be very close to the stone near the hilum in the posterior part. When the gland is pushed upward from outside, the course of the nerve can even be on top of the stone within the hilar area. It is still more of a challenge when the stone is located directly below the course of the nerve and recurrent inflammation has led to scar formation – a situation that can also occur from the external approach.
Preparation and Performance of the Procedure
General Requirements
Before starting the operative procedure, the patient must be informed about the procedures and possible risks of the interventions. These authors normally perform sialendoscopy and the combined transoral approach under local anesthesia. The advantage of this is that no instrument is needed to open the mouth or to move the tongue. Moreover, there is more tension of the muscle in the floor of the mouth and the patient can push the gland upward into the floor of the mouth and better expose the hilum and stones. All the different steps of the approach can be explained directly to the patient. A prospective study from Jokela et al. investigated the experience and compliance with 89 patients undergoing sialendoscopy or interventional sialendoscopy including transoral stone removal under local anesthesia with or without sedation. The subjective experience of discomfort and pain during the procedure was assessed as “mild” or “none” by 85% and 89%, respectively. No difference was seen between diagnostic and interventional procedures and 97% of patients would choose an operation under local anesthesia again. In transoral removal of hilar stones, 89% of the patients would be willing to have the operation repeated if necessary; 3% would choose the procedure under general anesthesia.
Straightforward cases are those with larger stones located within the middle of the floor of the mouth or in the main duct distal to the hilum. If the patient feels uncomfortable with a local anesthetic, or is a child, it can be performed under general anesthesia with trans-nasal intubation. The more difficult cases that may require general anesthesia are those with smaller impacted stones, which are not palpable within the hilum or even within the gland, when the size of the tongue is large, or the floor of the mouth is difficult to reach because of the anatomy of the mandible and teeth (deep floor of the mouth).
The patient is informed about typical side effects and possible complications. These include intraoperative and postoperative bleeding; pain during and after the procedure, especially during swallowing; postoperative infections and sialadenitis; remaining stones within the gland or stone recurrences; scar formation with obstruction of the duct; injury to the lingual nerve; developing a ranula (when ducts from the sublingual gland are affected); removal of the gland in a second step if the stone recurs or cannot be removed.
To minimize intraoperative and postoperative sequelae, the authors regularly administer perioperative antibiotics (i.e., cephalosporin or Augmentin or clindamycin in case of allergy), together with a single shot of 250 mg prednisolone intravenously. When a stone has been removed from the hilum or inside the gland, medication for pain is necessary, to allow regular gland massage by the patient for a constant salivary flow. Saline rinsing of the oral cavity helps reduce inflammation and supports wound healing.
Endoscopy
Preparation of instruments ( Fig. 18.3 ) and camera as well as monitor settings ( Fig. 18.4 ) precedes the superficial local anesthesia with Xylocaine Spray. The affected side of the floor of the mouth, as well as the oropharyngeal and laryngeal mucosa should be covered to reduce a gag response. Next, injection of a minimum of 5 mL of Ultracaine near the lingual nerve of the effected side from the hilum to the ostium in smaller increments. After dilation of the ostium ( Figs. 18.5 , 18.6 ) or surgical incision of the duct near the ostium ( Figs. 18.7 , 18.8 ), a diagnostic sialendoscopy can directly visualize size, mobility, and location of the stone ( Fig. 18.9 ). If the concrement is not removed by interventional sialendoscopy, the next step is to go directly ahead with a combined transoral removal. Sialendoscopy shows exactly the depth of the stone within the duct and a direct visualization within the duct system ( Fig. 18.10 ). This is very helpful for orientation during the surgical procedure. There are different approaches, including leaving the endoscope inside the duct as a guide to find the stone illuminated in front of the endoscope ( Fig. 18.11 ).
