Introduction
The submandibular gland is one of three paired major salivary glands that drains into the oral cavity. It is midway in size and location between the largest, the parotid gland, and the smallest, the sublingual gland. Histologically, it consists of both serous and mucinous acini, which collectively drain into an excretory duct that carries the secreted saliva into the oral cavity.
The gland is located within the submandibular triangle, superior and lateral to the hyoid bone and digastric sling, and inferior to the mandible. Its excretory duct, known as Wharton’s duct, passes deep to the mylohyoid muscle, paralleling the course of the lingual nerve. The duct and nerve lie immediately adjacent to the sublingual gland, just deep to the mucosa of the floor of the mouth. The duct opens through the sublingual papilla adjacent to the lingual frenulum ( Fig. 91.1 ). The narrowest point in the duct is at its orifice; therefore calculi that form in the gland may become impacted at the orifice and be visible or palpable in the floor of the mouth. Eighty percent of all salivary calculi are found in the Wharton’s duct. This is likely due to both the horizontal path of and the higher concentration of mucin in the Wharton’s duct. Impacted calculi that obstruct salivary outflow will result in enlargement of the gland, stasis of secretions, and ultimately inflammation of the gland (sialadenitis).
With age, the submandibular glands tend to become ptotic and assume a more inferior position, often even prolapsing lateral to the greater cornu of the hyoid bone. In this ptotic position, the gland may be mistaken for a neoplastic mass and lead to referral for further evaluation.
Key Operative Learning Points
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The marginal mandibular branch of the facial nerve lies within the operative field and must be either identified or avoided, depending on the situation.
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It is important to recognize that when a shoulder roll is placed and the patient’s head is rotated to the contralateral side, the marginal mandibular nerve is found more inferiorly and may lie directly over the gland.
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When excision of the gland is being performed for benign disease, identification of the nerve may not be necessary. In such cases the nerve may be protected by ligation and elevation of the facial vein (Hayes-Martin maneuver; Fig. 91.2 ).
Fig. 91.2
Exposure of the submandibular gland by elevating the platysmal muscle with the skin flap. Note the position of the marginal mandibular nerve (arrow) .
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When the gland is removed for malignancy or in conjunction with a neck dissection, the marginal mandibular nerve must be identified to allow the removal of the prevascular and postvascular nodes. Identification of the nerve will help to avoid injury of the nerve posterior to the gland, where the nerve may often be located a significant distance inferior to the level of the mandible.
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In cases in which there is extensive inflammation and scar tissue, a handheld nerve stimulator may be useful to help to locate and preserve the marginal mandibular nerve.
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The proximal stump of the facial artery should be double-ligated and the wound examined for bleeding vessels before closure.
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Care must be taken in patients who have had significant infection and scarring to ensure identification of the lingual nerve before sectioning Wharton’s duct.
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Care should be taken after the gland is freed posteriorly to visualize the hypoglossal nerve as it courses deep to the vessels, parallel to the submandibular duct. If inflammation hinders identification of the nerve, it is advisable to find the nerve inferior to the posterior belly of the digastric muscle and follow it in a posterior-to-anterior direction through the submandibular triangle to avoid injury.
Preoperative Period
History
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History of present illness
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Patients with sialadenitis often present with unilateral erythema, edema, and pain in the submental region that worsens with eating. Patients may also report foul-tasting (purulent) saliva, particularly when pressure is applied to the affected gland.
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Patients may present with a mass in the submandibular area.
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Neoplasms of the submandibular gland are not common and are more likely to be benign than malignant, but the finding of a mass in the submandibular gland merits further investigation to rule out malignancy.
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Signs or symptoms of nerve invasion, such as weakness of the tongue or lower lip or numbness of the tongue, suggest malignancy.
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Patients presenting for excision of the submandibular gland for chronic sialorrhea must be evaluated for duration and severity of the drooling, as well as for the underlying cause of the sialorrhea and its likelihood of improvement.
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Past medical history
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Medical history
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Collagen vascular disease such as Sjögren’s syndrome (or its symptoms)
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Prior radiation to the neck or treatment with I 131 increases the risk of sialadenitis and of salivary neoplasm.
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Surgical history
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Prior attempts at drainage, biopsy, or surgical removal of salivary calculi
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History of other neck surgery
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Social history
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Occupational exposure to silica dust or nitrosamines is linked to an increased risk of cancer of the salivary glands.
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Use of tobacco and alcohol
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Medications
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Antiplatelet drugs and anticoagulants
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Use of supplements that may predispose to bleeding
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Physical Examination
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Complete examination of the head and neck should be performed. Lymphadenopathy in the neck must trigger a full evaluation for suspected malignancy. Approximately one-quarter of cancers of the submandibular gland will have regional neck metastases.
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Visual examination and palpation of the floor of mouth may reveal a calculus in the distal Wharton’s duct.
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Bimanual palpation of the submandibular gland allows for evaluation of the size of the gland, presence of a discrete mass or calculus, tenderness of the gland to palpation, and degree of fixation of the gland to surrounding structures.
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The quality of the expressed saliva on each side should be evaluated and compared. Cloudy or purulent saliva suggests sialadenitis. The absence of salivary flow in the presence of an enlarged gland suggests obstruction of the outflow tract.
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A careful neurologic examination of the head and neck must be performed. Weakness of the tongue ipsilateral to the involved gland may be a sign of tumor or perineural invasion along the hypoglossal nerve. Likewise, numbness of the ipsilateral tongue may represent involvement of the lingual nerve. Facial weakness involving the ipsilateral lower lip is worrisome for malignant invasion of the marginal mandibular branch of the facial nerve.
Imaging/Diagnostics
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Ultrasound is useful for visualization of salivary calculi and for localization of a mass within the submandibular gland for fine-needle aspiration (FNA). Ultrasound can also show a dilated ductal system in cases of chronic sialadenitis.
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Computed tomography (CT) is most sensitive for identifying a calcified salivary duct calculus and should be ordered for patients presenting with acute or recurrent swelling of the gland with postprandial pain.
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Contrast is not indicated for sialolithiasis but should be used if neoplasm or severe infection with abscess is in the differential diagnosis.
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CT with intravenous (IV) contrast is the most useful modality in a known or suspected malignancy if there is suspicion of bone involvement or destruction.
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Magnetic resonance imaging (MRI) with IV gadolinium contrast is the imaging modality of choice for a suspected neoplasm of the submandibular gland. MRI is able to clearly delineate the neoplasm from the surrounding gland and can demonstrate invasion into nearby structures. In addition, MRI is the best modality for identifying evidence of perineural spread of tumor, which is especially important if adenoid cystic carcinoma is suspected.
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Sialography may reveal narrowing of the duct from scarring with secondary ductal ectasia within the hilum and the gland itself. However, sialography is contraindicated in an acutely infected gland, and MRI sialography has now essentially replaced this procedure.
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FNA is an important element in the diagnostic evaluation for suspected neoplasms of the salivary gland. However, a negative FNA is not definitive, and excision of the gland should still be performed for definitive diagnosis.
Indications
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Neoplasm or suspected neoplasm is an indication for excision of the submandibular gland. If FNA is nondiagnostic and the mass is confined to the gland, excision of the gland can be performed for diagnosis. For a known malignancy, more extensive excision including lymph node dissection is indicated.
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Sialolithiasis with subsequent duct obstruction and sialadenitis was formerly a common indication for excision of the submandibular gland. With the advent of sialoendoscopy, excision of the gland for this indication is now rare.
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In patients with dilated ectatic ducts and chronic infection, excision of the gland may still be necessary for chronic sialadenitis.
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Chronic sialorrhea in patients with neuromuscular swallowing disorders may be treated with submandibular gland excision. In such cases, this procedure is performed bilaterally and in combination with ligation of Stensen’s duct.
Contraindications
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Excision of the submandibular gland should be avoided in cases of acute infection due to loss of tissue planes and subsequent difficulty in identifying key structures. In fulminant cases in which abscess and elevation of the floor of mouth occur, incision and drainage, possibly even requiring tracheotomy, may be necessary; however, definitive gland excision can often be delayed until the acute inflammation has passed.
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Although not a contraindication, obstruction of the duct due to calculus, chronic sialadenitis, prior radiation, or Sjögren’s syndrome can sometimes be managed with sialoendoscopy. Minimally invasive procedures should be considered prior to proceeding with excision of the gland.
Preoperative Preparation
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FNA results and imaging should be reviewed preoperatively in patients with a mass in the submandibular gland.
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Anticoagulant/antiplatelet medications should be discontinued if possible.
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Several approaches to excision of the submandibular gland have been described, and the choice of approach should be made before surgery.
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The lateral transcervical approach is the traditional approach to excision of the submandibular gland and remains the most commonly used approach despite the description of newer approaches in recent years.
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The intraoral approach is designed to avoid visible scarring from the cervical incision and injury to the marginal mandibular nerve, which is the most frequently injured nerve in the traditional transcervical approach. Branches of the facial nerve are not at risk with the intraoral approach and are not identified during this dissection.
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Pitfalls of the intraoral approach stem from significant retraction of the floor of the mouth, including the lingual nerve and mylohyoid muscle. In one study, temporary injury to the lingual nerve was observed in 81% of patients, and 68% reported a temporary decrease in tongue mobility that resolved within 2 weeks of surgery and was attributed to edema of the floor of the mouth rather than injury to the hypoglossal nerve.
Operative Period
Anesthesia
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General anesthesia is preferred; however, excision of the submandibular gland may be performed under local anesthesia in patients who are poor candidates for general anesthesia as long as the gland does not have findings suspicious for malignancy.
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Paralysis should be avoided to aid in identification of the marginal mandibular and hypoglossal nerves, especially in cases with suspected malignancy or a history of recurrent infection.
Positioning
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For the transcervical approach, placement of a shoulder roll is used to extend the neck and provide better exposure of the submandibular triangle. The patient is then positioned with the head elevated slightly and rotated toward the opposite side.
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Orotracheal intubation is performed for the transcervical approach, and the tube is taped to the side contralateral to the surgical site.
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Nasotracheal intubation is necessary for the intraoral approach.
Perioperative Antibiotic Prophylaxis
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Antibiotic prophylaxis is not required when using the transcervical approach because this is a clean procedure according to the Centers for Disease Control and Prevention (CDC) surgical site infection guidelines.
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Transoral excision is a clean-contaminated procedure, and a 24-hour course of prophylactic antibiotics covering oral flora is recommended.
Monitoring
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Nerve monitoring is not routinely performed during excision of the submandibular gland.
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Handheld nerve monitoring without the use of IV paralytics may be useful in cases of suspected malignancy or severe chronic infection where surgical planes may be lost.
Instruments and Equipment to Have Available
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Head and neck surgical set
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Bipolar electrocautery
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Handheld nerve monitor
Key Anatomic Landmarks
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The facial vein will be identified on the lateral surface of the submandibular gland. Ligation and elevation of this vein will help to preserve the marginal mandibular nerve (Hayes-Martin maneuver) (see Fig. 91.2 ) in cases in which the adjacent prevascular and postvascular nodes do not require dissection.
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The anterior belly of the digastric muscle should be identified and reflected posteriorly to expose the mylohyoid muscle.
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The mylohyoid muscle is an important landmark in that the lingual nerve and Wharton’s duct, as well as the sublingual gland and the anterior portion of the submandibular gland, lie immediately deep to it.
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The posterior belly of the digastric muscle may be used to help identify the hypoglossal nerve in cases in which inflammation makes identification of the nerve difficult. The hypoglossal nerve may be found inferior to the posterior belly of the digastric muscle and then can be followed in a posterior-to-anterior direction through the submandibular triangle.
Prerequisite Skills
General surgical skills and an intimate knowledge of the anatomy of the head and neck
Operative Risks
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Injury to the marginal mandibular nerve
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Injury to the hypoglossal nerve
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Injury to the lingual nerve
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Retained calculus with possible obstruction and infection
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Hemorrhage from the facial artery with possible hematoma and elevation of the floor of mouth
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Wound infection
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Fistula formation
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Unsightly scar
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Xerostomia
Surgical Technique
Transcervical Approach
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The incision is made at the inferior margin of the submandibular gland in a natural skin crease, usually slightly above the level of the hyoid bone.
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Localization of a smaller submandibular gland can be simplified by placing a gloved finger in the mouth and depressing the floor of the mouth on the affected side.
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The incision is carried through skin, subcutaneous tissue, and platysma muscle. Once through the platysma muscle, the nerve is at risk, and dissection should first be directed toward the inferior portion of the submandibular gland.
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After exposure of the submandibular gland, the fascia overlying the gland is incised and the superior flap of fascia is elevated from the lateral surface of the gland. As this is performed, the facial vein is encountered. Ligation and elevation of this vein will help preserve the marginal mandibular nerve (see Fig. 91.2 ).
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If the gland is excised as a part of a neck dissection or if the gland is being excised for possible malignancy, the nerve must be dissected free of the underlying vein and adjacent prevascular and postvascular nodes ( Fig. 91.3 ), which should be removed.
