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Submandibular gland anatomy

Overview

  • Mixed mucous and serous gland
  • Large superficial part and a small deep part
    • Continuous with one another round the free posterior margin of the Mylohyoid muscle
  • Lies in the Digastric Triangle
    • Anterior border: Anterior Belly of the Digastric
    • Posterior border: Posterior Belly of the Digastric
    • Lateral border: Lower border of the Mandible and Medial Pterygoid Muscle
    • Floor: Hyoglossus and Mylohyoid
    • Roof: Skin, Platysma, Investing Layer of Cervical Fascia

Superficial part

  • Three surfaces – lateral, inferior and medial
  • Lateral surface:
    • Lies against the Submandibular Fossa of the Mandible
    • Overlaps the front of the Medial Pterygoid insertion
    • Deeply grooved posteriorly by the Facial Artery
      • Facial Artery hooks under the Mandible to reach the face at the front of the Masseter muscle
  • Inferior/Superficial surface:
    • Covered by skin, Platysma and Investing Fascia
    • Crossed by the Facial Vein and Cervical Branch of the Facial Nerve
    • Crossed sometimes by the Marginal Mandibular Branch of the Facial Nerve
      • Nerves lie outside the Investing Fascia
    • Submandibular Lymph Nodes lie in contact with the surface of the gland and within its substance
      • Thus, the need to remove the gland as well as nodes in the operation of radical neck dissection
  • Medial surface:
    • Lies against Mylohyoid
    • Behind Mylohyoid, it is related to:
    • Facial Artery initially deep to the gland and then grooves the posterosuperior part as it hooks over the top of the gland on its lateral surface

Deep part

Submandibular Duct (of Wharton)

  • Length: 5cm – same length as Parotid Duct
  • Emerges from medial surface of the Deep Part of the Submandibular Gland
    • Near the posterior border of Mylohyoid
  • Runs with the deep part – forwards and slightly upwards
    • First between Mylohyoid and Hyoglossus
    • Then between Sublingual Gland (lateral) and Genioglossus (medial)
  • Opens into floor of mouth on the Sublingual Papilla beside the Frenulum of the Tongue
  • As it lies on Hyoglossus, the duct is crossed laterally by the Lingual Nerve
    • Which then turns under the duct to pass medially to the Tongue
  • Consequences of damaging Lingual Nerve:
    • Altered salivary secretion on the affected side
    • Loss of taste to anterior 2/3rd of tongue
    • Sensory changes to the anterior 2/3rd of tongue and floor of mouth
  • Consequences of damaging Hypoglossal Nerve:
    • Loss of motor innervation to all intrinsic muscles of tongue except Palatoglossus
  • Consequences of damaging Marginal Mandibular Nerve:
    • Facial asymmetry and drooling
    • Supplies Depressor Anguli Oris, Depressor Labii Inferioris, Risorius, and part of Obicularis Oris

Blood Supply

Lymph Drainage

  • Submandibular Lymph Nodes

Nerve Supply

  • Secretomotor fibres – Cell bodies in the Submandibular Ganglion
    • Hangs suspended from the Lingual Nerve on the surface of Hyoglossus
    • Pre-ganglionic fibres pass from cell bodies in the Superior Salivary Nucleus in the Pons by way of: Nervus Intermedius ⇒ Facial Nerve ⇒ Chorda Tympani ⇒ Lingual Nerve
    • Post-ganglionic fibres pass to Submandibular Gland and also to Lingual Nerve for transmission to the Sublingual Gland
  • Sympathetic (Vasoconstrictor) fibres – Plexus around the Facial Artery

Development

  • Ectodermal groove in the floor of the mouth becomes converted into a tunnel whose blind end proliferates to form the secreting acini.
  • Develops during 6th week of gestation (after Parotid Gland)

Summary of Important Anatomical Relations

  • Superficial: Mandibular and Cervical Branches of the Facial Nerve
    • Mandibular and Cervical branches emerge from Parotid Gland near angle of Mandible
    • Mandibular branch runs downwards and forwards deep to Platysma
    • Curves upwards to cross Mandible close to Facial Artery
    • Mandibular nerve protected during surgery by making incision 4cm below Mandible
  • On the gland: Facial Artery and Vein
    • Facial Artery
      • Originates from External Carotid Artery
      • Passes upwards
      • Identified at the posterior aspect of the Submandibular Gland
      • Passes forwards above the gland
      • Emerges beneath the lower border of the Mandible
      • Curls upwards along the face
    • Facial Vein
      • Descends along the face from anterior to posterior
      • Crosses the Mandible about 2cm in front of the angle
      • Runs along the external surface of Submandibular Gland and receives the Submental Vein forming the Common Facial Vein
      • Continues to drain into the Internal Jugular Vein
    • Facial Artery and Vein usually encountered after identification and preservation of the Mandibular Nerve
      • Usually ligated at this point and again at the posterior aspect of the gland
  • Deep: Lingual and Hypoglossal Nerves and Submandibular Ganglion
    • Lingual Nerve:
      • Deep to Mylohyoid
      • Above the deep part of the Submandibular Gland
      • Runs forward between Mylohyoid and Hyoglossus
      • Passes around the Submandibular Duct by initially passing from medial to lateral above the duct then curving underneath the duct from Lateral to medial, emerging at the medial side of the duct
      • During ligation of Submandibular Duct, care must be taken to identify the lingual nerve so that it is not damaged
      • More proximally, the Lingual Nerve is identified by retracting the Submandibular Gland laterally and the Mylohyoid muscle anteriorly
      • Lingual Nerve is freed from the Submandibular Gland by dividing between the nerve and the Submandibular Ganglion
    • Hypoglossal Nerve:
      • Lies deep and below the Submandibular Gland
      • Runs between the Mylohyoid and Hyoglossus muscles
      • Nerve identified after posterior border of the gland is mobilised and retracted upwards
      • Mylohyoid also retracted anteriorly to expose the nerve as it emerges from the Posterior Belly of Digastric

See: Submandibular gland excision

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