Salivary gland ductal diversion or relocation, salivary ductal ligation, and botulinum toxin injection in the salivary glands are effective strategies in the treatment of drooling or sialorrhea. The latter is mostly caused by the inability of the patient to control oral secretions rather than by an increased production of saliva. Patients may suffer from anterior drooling, posterior drooling, or both. Anterior drooling is defined as saliva spilling from the mouth. This can lead to social rejection, isolation, poor hygiene, and an increased burden of care on the family. In patients with posterior drooling, saliva spills through the oropharynx and into the hypopharynx with potentially serious medical complications including chronic aspiration and chronic lung disease. Viewed by some as a cosmetic issue, drooling may lead to serious medical complications such as choking, pneumonia, feeding issues, skin infections and speech problems. 1
While nonsurgical treatment options exist for sialorrhea, including rehabilitation (oral motor and behavior therapy) and medication (anti-cholinergic), tailored surgical options give rapid long-lasting results especially in patients with moderate or severe anterior drooling who failed conservative approaches and those with posterior drooling. Also many patients benefit from a combination of different treatment modalities.
This chapter highlights the surgical anatomy, preoperative preparation, technical details, and pearls to avoid intraoperative complications of submandibular gland ductal relocation or diversion, Wharton and Stenson’s ductal ligation, and botulinum toxin injection in the salivary glands.
12 Salivary Gland Ductal Diversion, Botulinum Toxin Injection, and Salivary Ductal Ligation
12.1 Pathophysiology of Drooling and Surgical Anatomy
The parotid and submandibular glands are paired major salivary glands responsible for most of the salivary output in the oral cavity (▶ Fig. 12.1). The rest of the saliva is produced by the sublingual glands and minor glands located mainly in the palatine and oral mucosa. Between 0.5 and 1.5 L of saliva are secreted daily in children. 2 Saliva is composed of mostly water (99%), and contains electrolytes, proteins, and enzymes. Secretions from the parotid glands are mostly serous in nature with high water content and lower mucin content, while submandibular gland secretions are more viscous with mixed mucous and serous saliva. The submandibular glands produce most of the resting salivary secretions, while the parotids are responsible for the bulk of stimulated saliva during feeding. Drooling is considered pathological if it persists after the age of 4 years in healthy children with normal development. 1 , 3 It is typically caused by the inability of the patient to control oral secretions rather by an increased production of saliva 1 and is more commonly seen in patients with neurological disorders. Patients may suffer from anterior drooling, posterior drooling, or both. Anterior drooling is defined as saliva spilling from the mouth. This can lead to social rejection, isolation, poor hygiene, and an increased burden of care on the family. In patients with posterior drooling, saliva spills through the oropharynx into the hypopharynx, with potentially serious medical complications including chronic aspiration and progressive lung disease.
The parotid and submandibular salivary glands do not differ in size in children with or without drooling. 4 The parotid is the largest major salivary gland. It lies between the external auditory canal, the ramus of the mandible, and the mastoid tip, and it is separated from the submandibular gland by the stylomandibular ligament. The parotid is artificially divided by the facial nerve into a deep and a superficial lobe. The submandibular gland is composed of a larger superficial lobe located in the submandibular triangle between the anterior belly and the tendon of the digastric muscle, and a smaller deep lobe that hooks around the posterior margin of the mylohyoid entering the oral cavity through a triangular aperture as it lies on the lateral surface of the hyoglossus.
Both submandibular and parotid glands are formed by an aggregate of multiple secretory units composed of acini and ducts. Saliva produced by the secretory cells of the acini passes through intercalated, intralobular, and excretory ducts, before collecting in Stensen’s and Wharton’s ducts, which are the main excretory ducts of the parotid and the submandibular, respectively. Stensen’s duct is 4 to 7 cm in length, and about 0.5 to 1.4 mm in diameter. 5 It arises from the anterior border of the parotid gland, runs superficial to the masseter muscle parallel to and below the zygoma, then turns sharply, pierces the buccinator, and enters the oral cavity opposite the second upper molar. Some patients have accessory parotid glands located at variable distances from the main gland along the duct. 6 Wharton’s duct emerges from the deep lobe of the submandibular gland and courses anteriorly, deep to the mylohyoid muscle and lateral to hyoglossus and genioglossus. It runs medial to the sublingual gland before opening into an orifice in the sublingual papilla lateral to the lingual frenulum. Wharton’s duct is 5 cm long, and has a mean diameter ranging between 0.5 and 1.5 mm. 5 During submandibular duct relocation or diversion as well as ductal ligation, the surgeon has to be cognizant of important anatomical relationships of the lingual nerve vis-à-vis the duct (▶ Fig. 12.1). The lingual nerve starts superior to the submandibular duct and then, as it descends forward, it crosses the lateral side of the duct, passes below the duct winding round its lower border, before crossing it medially and ascending toward the genioglossus proceeding antero-medially to terminate as medial branches providing general somatic afferent innervation to the anterior two-thirds of the tongue. The hypoglossal nerve emerges from behind the posterior belly of the digastric muscle and courses along the floor of the submandibular triangle lying deep to the submandibular gland. It passes forward into the gap between the hyoglossus medially and the myelohyoid laterally and supplies innervation to the intrinsic and extrinsic muscles of the tongue.
Salivary flow is controlled by the autonomic nervous system. The parotid glands receive parasympathetic secretomotor innervation from fibers arising in the inferior salivatory nucleus. These fibers travel with the glossopharyngeal nerve, leave it as Jacobson’s nerve passing through the middle ear space in the tympanic plexus, and then exit the temporal bone as the lesser petrosal nerve. The latter leaves the middle cranial fossa through the foramen ovale, where preganglionic fibers synapse in the otic ganglion. The postganglionic fibers travel with the auriculotemporal nerve to supply the parotids.
The submandibular and sublingual glands receive innervation from preganglionic fibers originating in the superior salivatory nucleus. These fibers leave the brainstem as the nervus intermedius to join the facial nerve, and then leave it with the chorda tympani in the mastoid segment, through the middle ear, and petrotympanic fissure to the infratemporal fossa. They are then carried by the lingual nerve before they synapse in the submandibular ganglion. Postganglionic fibers innervate the submandibular and sublingual glands. This parasympathetic postganglionic cholinergic innervation leads to the secretion of large amounts of low-protein, serous saliva. Sympathetic innervation of the glands happens via preganglionic nerves in the thoracic segments T1–T3, which synapse in the superior cervical ganglion. Postganglionic sympathetic innervation is through the external carotid plexus, with postganglionic neurons releasing norepinephrine. Sympathetic stimulation causes the secretion of a small amount of high protein thicker saliva.
12.2 Mechanism of Action of Botulinum Toxin
Botulinum toxin is thought to inhibit the release of presynaptic acetylcholine at the neuroglandular junction leading to reduction of salivary secretion. The toxin has a heavy and a light chain. The former attaches to proteins on the surface of axon terminals, allowing toxin uptake into neurons by endocytosis. The light chain has protease activity. Type A toxin degrades a synaptosomal-associated protein (SNAP-25) preventing neurosecretory vesicles from docking with the nerve synapse plasma membrane and from releasing their neurotransmitters leading to chemical parasympathetic denervation of the gland. The latter occurs 48 to 72 hours following the injection and lasts on average for 3 to 6 months. 7 , 8 This explains why patients require repeated injections for drooling control. 9 – 11 Botulinum Toxin B binds to another presynaptic receptor protein called vesicle-associated membrane protein (VAMP) with similar effects. 12 Botulinum toxin use for the treatment of sialorrhea is still considered off-label. There are currently three botulinum toxin A products and one botulinum toxin B that have been used clinically for sialorrhea in various centers. These are onabotulinumtoxin A (BOTOX, Allergan Inc., Irvine, CA, USA), incobotulinumtoxin A (Xeomin, Merz Pharma Ltd, Germany), abobotulinumtoxin A (Dysport, Ipsen Ltd, UK), and rimabotulinumtoxin B (Botulinum Toxin B, Myobloc, Solstice Neurosciences, San Francisco, CA). 13 These are not identical and should not be considered interchangeable as they differ in molecular structure, and/or manufacturing processes. 14 One unit of Botox is comparable to one unit of Xeomin, to about 3 to 4 units of Dysport, and to 20 to 30 units of Myobloc (in certain publications). 15 These conversion ratios should be used with caution and vary in the literature and according to indications.
12.3 Preoperative Evaluation
12.3.1 Clinical Evaluation
A majority of patients referred for anterior drooling under the age of 4 years benefit from a conservative approach and improve over time. Knowledge of the underlying etiology and the progress or evolution of the patient’s condition is essential prior to offering surgical treatment. It is very important to review all the medications of the patient as certain antipsychotics, sedatives, and cholinergic agonists can increase salivation. 16 , 17 Also in many patients with developmental delay, there could be a slower progress in oral motor function that can persist until the age of 6 years.
In view of the diverse etiologies of drooling and the limitations of approaches relying on a single-treatment modality, the author has founded a multi-disciplinary Saliva Management Clinic, described elsewhere. 1 An interdisciplinary approach to children with sialorrhea, whereby each patient is offered a number of rehabilitative, medical, and surgical options based on a consensus recommendation of the team ensures that patients get access to the options that best suit their needs.
When assessing patients referred for surgery, it is essential to evaluate if their drooling is anterior, posterior, or mixed. This guides the surgeon as to the best treatment modality for the patient. For example salivary duct relocation should never be performed in posterior drooling, as it will only worsen the problem. Symptoms of posterior drooling include congested breathing, coughing, gagging, a wet voice, and at times, penetration into the airway, and aspiration pneumonia. 18 , 19 All patients should undergo a flexible upper airway endoscopy to detect adenoid hypertrophy, airway obstruction, laryngeal pooling, and laryngeal penetration or aspiration. This assessment can also help in predicting a difficult intubation. The oral cavity should be examined for gingivitis, dental caries, and occlusion issues. The face should be examined for peri-oral erythema. The head and body posture should also be assessed as well as the efficiency of swallowing and the overall nutritional status. The lungs should be auscultated.
The severity of the drooling problem and its impact on the patient and family also helps the treating physician select the most appropriate treatment. Tools to quantify this include weighing oral rolls or bibs, counting the number of bib changes per day, the Teacher’s Drooling Scale, the Drooling Frequency and Severity Scale, the Visual Analogue Scale (VAS), and the Drooling Impact Scale. 20 – 23 The Drooling Quotient (DQ) can be calculated by determining, for every interval of 15 seconds, the presence or absence of drooling over a 10-minute period. Drooling episodes are counted in the 40 observations made, and the drooling score is calculated as percentage. Traditionally, it is done when the child is resting and another time during activities. DQ can be difficult to measure in non-cooperative patients. 21 Our group concurs with others that the DQ calculated over 5 minutes during which the child is engaged in an activity to be equivalent to the 10 minutes score as an accurate representative measure of anterior drooling. 24 Specific questions should be asked to detect any effect of drooling on self-esteem, social interaction, quality of life, and burden of care. 1
Our group has developed a tool, Daniel drooling impact score (DDIS) scale that helps us document and quantify an impact score for the drooling on the patient and their family (▶ Table 12.1). DDIS is based on the severity as well as the medical and social effects of drooling. This score has helped us guide the recommendations of therapeutic options based on the severity of the impact. The postoperative score also assists us in evaluating the effect of surgery on the quality of life and health of our patients.