10.1 Surgical Anatomy

The submandibular glands are paired major salivary glands containing both serous and mucinous acini. Each gland is composed of a superficial lobe that extends inferior to the posterior half of the body of the mandible, and a 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 (▶ Fig. 10.1). The superficial lobe, which accounts for the greater portion of the gland, is located in the submandibular triangle, between the anterior belly and the tendon of the digastric muscle. It is bounded superomedially by the mylohyoid muscle, and inferiorly by the investing layer of the deep cervical fascia and platysma. Each submandibular gland drains into an excretory duct, also known as Wharton’s duct that emerges from its deep lobe, and courses anteriorly, deep to the mylohyoid muscle and lateral to hyoglossus and genioglossus. It abuts the sublingual gland below the mucosa of the floor of the mouth before opening into an orifice in the sublingual papilla lateral to the lingual frenulum (▶ Fig. 10.2). This opening is the narrowest part of the duct and is dilated prior to sialoendoscopy. The submandibular glands are small in young infants and are contiguous to the sublingual glands. They grow rapidly during the first 2 years of life.

During submandibular gland excision the surgeon has to be cognizant of important anatomical relationships of the lingual nerve, the hypoglossal nerve, and the marginal mandibular branch of the facial nerve (MMN). The latter is the most vulnerable during submandibular gland surgery particularly in young children as it is located higher than in adults often taking a superficial course over the mandible, and portions of it may be exposed due to limited parotid gland development. It usually exits the anteroinferior portion of the parotid gland close to the angle of the mandible and traverses the margin of the mandible in the plane between platysma and the investing layer of deep cervical fascia covering the submandibular gland. When the MMN descends below the border of the mandible, it usually runs superficial to the anterior facial vein and immediately over the superficial lobe of the submandibular gland. Strategies to avoid injuring the marginal mandibular nerve (MMN) include making the incision 2 fingerbreadths inferior and parallel to the body of the mandible, or slightly above the level of the hyoid bone. Another strategy is to ligate the facial vein and retract it cephalad so that the MMN is included in the superior flap and protected.

Posteriorly, the lingual nerve is above the duct, 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 towards the genioglossus. It terminates as several medial branches ascending on the external and superior surface of hyoglossus to provide general somatic afferent innervation to the mucous membrane of 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.

10.2 Preoperative Evaluation

A detailed history and physical examination are of utmost help in diagnosing the specific salivary gland disorder. The differential diagnosis includes acute or chronic inflammatory (and/or infectious) conditions, congenital lesions, benign or malignant tumors, vascular malformations, and manifestations of systemic diseases. In a recent retrospective review of 193 patients post submandibular gland excision, 56% had non-neoplastic disorders (sialolithiasis and sialadenitis) while the remaining had a submandibular gland tumor. The most common benign neoplasm was pleomorphic adenoma (27%). Ten percent of tumors were malignant and included adenoid cystic carcinoma, mucoepidermoid carcinoma, and adenocarcinoma. ¹

Important elements on history include the onset, duration, severity, and frequency of the symptoms. Perinatal salivary gland swelling is more likely to be secondary to a congenital lesion such as a lymphatic or vascular malformation. A gradual painless increase in size suggests a neoplasm, especially in older children. ² An acute onset of pain and swelling, especially with fever, indicates an infectious or inflammatory lesion. Ductal obstruction often presents with intermittent and/or recurrent postprandial swelling. Painless violaceous lesions of the skin are often seen with atypical mycobacteria infections or cat scratch disease (▶ Fig. 10.3). A history of trauma suggests ductal injury.

Physical examination should include inspection of the floor of the mouth, as well as bimanual palpation of the gland and duct. The quality of the saliva expressed at the papilla should be inspected for purulence. An enlarged submandibular gland with decreased or absent salivary flow suggests obstruction secondary to a stone or ductal stenosis. In cases of acute infection the patient is prescribed antibiotics and elective surgery is planned at a later date.

Indications for submandibular gland excision are listed in ▶ Table 10.1. It is the author’s belief that the management of sialolithiasis and ductal pathology should aim for gland-sparing procedures before considering gland excision. Sialoendoscopy is now well established as a minimally invasive and effective tool for the diagnosis of salivary gland ductal pathology (inflammation, stenosis, stricture), as well as the treatment of sialolithiasis. Despite advances in sialoendoscopy indications remain for gland removal in chronically inflamed gland with recurring episodes of painful swelling whereby conservative treatment options have failed, and symptomatic or recurrent sialadenitis caused by intraparenchymal stones or large stones not amenable to sialoendoscopy and lithotripsy. Gland removal may also be indicated in patients with recurrent calculus formation (▶ Fig. 10.4), intraoperative complications of sialendoscopy, inability to extract the stone during minimally invasive procedures, and residual symptoms despite stone removal. In rare cases acute inflammation transforms into Ludwig’s angina with elevation of the floor of the mouth and tongue by the inflammatory phlegmon and tissue edema adjacent to the gland. In these patients, the airway can be protected with fiberoptic intubation.

Bilateral submandibular gland excision combined with bilateral parotid duct ligation is an effective surgical procedure for the treatment of patients with severe sialorrhea or aspiration. ³ A long-term follow-up study reported significant improvement in 87% of patients with no major complications and only 8% experiencing xerostomia. ⁴ In less severe cases, bilateral submandibular gland excision can be performed without parotid duct ligation to avoid the latter complication.

Several imaging modalities can be helpful preoperatively. While plain X-rays may detect radiopaque stones, they miss radiolucent ones. Ultrasound remains the most helpful test in the pediatric population, because of its non-invasiveness and lack of radiation exposure. Ultrasound can detect up to 90% of stones greater than 2 mm, and can distinguish benign from malignant lesions in the majority of cases. ^{5 , 6} Ultrasound can also help differentiate whether masses are intraglandular or extraglandular. ² CT at times provides complementary information to distinguish gland enlargement from an intraglandular mass versus a mass abutting the gland.

CT and/or MRI are important to assess parapharyngeal extension, deep cervical lymphadenopathies, as well as skull base extension. CT can also be useful for surgical planning in inflammatory conditions such as sialadenitis, ductal stones or stenosis, ranulas, and abscesses. CT is also useful to detect bony erosion in cases of tumors. Preoperative knowledge of the presence of calculi in the duct is important as failure to excise the duct up to the floor of the mouth can result in retained fragments, which can lead to chronic inflammation or recurrent infections.

Despite the ionizing radiation, the CT scan has the advantage of being a short procedure as opposed to MRI. MRI with IV gadolinium contrast remains the test of choice in cases suspicious for an underlying neoplasm and in lesions of the parapharyngeal space as it provides excellent soft tissue detail. Flow voids also assist in determining the nature of vascular malformations. Newer MR techniques can help delineate benign from malignant processes using dynamic contrast or diffusion-weighted methods. A sialogram may reveal narrowing of the duct from scarring and secondary ductal ectasia within the hilum and the gland itself.

While fine needle aspiration biopsy (FNAB) can be very useful in the work-up of suspected neoplasm of the submandibular gland, a negative FNAB is not definitive and the surgeon should still proceed with gland resection for final diagnosis. Also in cases of a malignancy a nodal neck dissection is indicated.