Submandibular Gland Resection

Submandibular Gland Resection

EMBRYOLOGY

The paired submandibular glands develop from the buds in the floor of the primitive mouth that grow on the lateral aspect of the tongue. The buds initially give rise to cords that canalize into ducts, and their ends differentiate into the acinar structures.

ANATOMY

The submandibular gland is located in the floor of the mouth and consists of a larger superficial part that communicates with a smaller deep part around the posterior border of the mylohyoid. The superficial part primarily lies within the digastric triangle and is bounded superomedially by the mylohyoid muscle, superolaterally by the mandible, and inferiorly by the skin platysma and investing layer of the deep cervical fascia. The facial artery is related to the posterior surface of the submandibular gland.

The deep part of the submandibular gland is located in the interval between the mylohyoid and the hyoglossus muscle. Emerging from the deep part of the gland is the submandibular duct (Wharton’s duct), which opens at the base of the frenulum in the floor of the mouth. Other important structures that lie in the vicinity of the deep part of the submandibular gland are the lingual nerve, the submandibular ganglion superiorly, and the hypoglossal nerve inferiorly.

The blood supply of the submandibular gland is through branches of the facial and lingual arteries, and the venous drainage follows the respective facial and lingual veins. The parasympathetic secretomotor supply is from the superior salivary nucleus of the seventh cranial nerve. These fibers reach the submandibular ganglion via the chorda tympani and submandibular ganglion.

PREOPERATIVE PREPARATION

Apart from basic investigations, the imaging studies of the submandibular gland, particularly plain radiograph of the floor of the mouth, sialogram for recurrent submandibular gland enlargement, or computed tomography of the neck for a solitary mass within the submandibular gland, are reviewed. Although indication for resection of the submandibular gland is usually based on clinical suspicion, results of fine-needle aspiration cytology, if performed, should be reviewed. Preoperatively the surgeon must determine by physical examination whether the hypoglossal, lingual, and marginal mandibular branches of the facial nerve are intact. Informed consent is obtained after the patient is informed about the risks of damage to the hypoglossal nerve, the lingual nerve, and the marginal mandibular branch of the facial nerve.

Operative Procedure

POSITION

The patient undergoes general anesthesia with endotracheal intubation, but anesthesiologists must refrain from using paralyzing agents because these may make the use of the nerve stimulator ineffective. The patient is placed in a supine position with a shoulder roll to extend the neck. The head is turned away from the affected side and elevated to a 45-degree position to reduce venous congestion. The operative area is prepped and draped. The face is left exposed by placing a transparent dressing to allow facial movements to be observed during facial nerve stimulation.

INCISION

An incision about 2 cm below and parallel to the body of the mandible is marked with an indelible pen Fig-A. The skin is infiltrated with 1% lidocaine with epinephrine to avoid bleeding from the skin. The skin is incised with a no. 15 scalpel.

Figure : A, Incision used to perform submandibular gland resection. Important anatomic structures are shown. B, Mylohyoid muscle is retracted to expose the submandibular duct and lingual and hypoglossal nerves.

EXPOSURE AND OPERATIVE TECHNIQUE

The dermis is divided with cutting electrocautery down to the level of the platysma. In line with the incision, the platysma is also divided, and then superior and inferior flaps are created in the subplatysmal plane. Superiorly, the surgeon should be cognizant of the presence of the marginal mandibular branch of the facial nerve. The facial artery and vein will be encountered running deep to this nerve, and they are divided and ligated. In fact, retracting these vessels upward will protect the marginal mandibular branch of the facial nerve during subsequent dissection (Hayes-Martin maneuver). The superior border of the gland is freed from the body of the mandible.

Dissection now proceeds toward the posterior aspect of the gland, and the posterior/common facial vein is exposed, isolated, divided, and ligated. Posteriorly, the gland is carefully elevated off the surface of the sternocleidomastoid muscle. Retracting the anterior border of the sternocleidomastoid muscle will expose the tortuous facial artery, which is ligated again. The superficial part of the submandibular gland is elevated from the underlying mylohyoid muscle. The posterior border of the mylohyoid muscle is identified and then retracted anteriorly with a loop retractor. This should expose the deep part of the submandibular gland and the important adjacent structures Fig B. These include the lingual nerve above and the hypoglossal nerve below.

Superiorly the branches from the lingual nerve to the submandibular ganglion are seen and divided. This allows the lingual nerve to retract superiorly and thus avoids injury. Next, the hypoglossal nerve, which will be seen emerging from beneath the anterior belly of the digastric muscle, is identified. The gland now remains attached only by its submandibular duct (Wharton’s duct), lying between the lingual and hypoglossal nerves. The submandibular duct is clamped, divided, and ligated with 2-0 absorbable sutures. The operative area is inspected for hemostasis, and the retracted marginal mandibular nerve is returned to its normal position.

CLOSURE

A 7-mm Jackson-Pratt drain is placed in the operative field. The platysma is approximated, with care taken not to entrap the already preserved marginal mandibular nerve. The skin is closed with 5-0 absorbable sutures.