Excision of submandibular gland
Indications
[edit | edit source]- Chronic sialadenitis
- Sialectasis
- Sialolithiasis
- Benign and malignant tumours
- As part of a neck dissection
Principles
[edit | edit source]- Excise gland
- Avoid injury to marginal mandibular, lingual and hypoglossal nerves
Important structures
[edit | edit source]- Submandibular triangle
- Digastric - no important structures lateral to the muscle; facial artery immediately medial to posterior belly
- Mylohyoid - forms floor of submandibular triangle and separates oral from cervical part of SMG - no important structures superficial to it, but lingual nerve and hypoglossal nerve are deep to it
- Marginal mandibular nerve - at risk of injury, passes down on surface of ramus of mandible then may loop up to 3cm below mandible before coming back up over mandible
- Lingual nerve - large flat nerve running in lateral floor of mouth above SMG
- Hypoglossal nerve - enters the submandibular triangle posteroinferiorly and medial to the hyoid bone, crosses in an anterosuperior direction, and exits into mouth behind mylohyoid muscle. Covered by a thin layer of fascia, distinct from SMG capsule, and accompanied by thin-walled ranine veins that are easily torn.
- Nerve to mylohyoid - generally not looked for or preserved, but can cause contraction of mylohyoid/anterior belly of digastric when mobilising SMG off mylohyoid
- Common facial and facial veins
- Facial artery - enters submandibular triangle posteroinferiorly, moving to superior where it joins facial vein to cross the mandible
Technique
[edit | edit source]- Avoid paralysis
- Position supine with neck extended and head rotated to the opposite side
- Drape to expose lower lip, lower margin of mandible, and upper neck
- Incise skin horizontally, at least 3cm below mandible, extending parallel with mandible between anterior SCM and a point 2cm lateral to midline
- Dissect through fat and platysma to expose facial vein crossing over SMG and EJV. May need to ligate some small vessels.
- Facial vein ligated and divided inferiorly
- Incise fascial covering of SMG parallel to and just above the hyoid
- Subcapsular resection of the SMG with inferior traction on SMG, until superior margin of SMG is reached. Lift the facial nerve/investing fascia superiorly to protect the marginal mandibular branch which passes superficial to it (Hayes-Martin manoeuvre)
- Dissect bluntly immediately above SMG to identify facial artery and vein. Look out for marginal mandibular nerve looping down from mandible, but don't need to search for it.
- Divide facial artery and vein close to SMG
- Mobilise inferior margin SMG from anterior belly digastric, then proceeding anteriorly as far as posterior border of mylohyoid, elevating SMG from mylohyoid in the floor of the submandibular triangle. Mylohyoid nerve and vessels can be encountered here but can be divided.
- Now work upwards along the posterior border of mylohyoid. Passing between hyoglossus and mylohyoid you may identify lingual nerve (anterosuperior), submandibular ganglion (anterior, running into gland), and submandibular duct (off anterior surface). Retract the gland down, and can continue dissecting right on the surface of gland. Leave the duct to last, once other structures have been identified.
- Might identify hypoglossal nerve in floor of digastric triangle then passing between mylohyoid and hyoglossus, but don't usually see it.
- Clamp, divide and ligate the submandibular duct (watch carefully for lingual nerve)
- Reflect SMG inferiorly and free from tendon and posterior belly of digastric and remove
- Wound irrigated and closed in layers with Vicryl to platysma and subcuticular suture to skin
- Consider drain