What is the most likely cause of drooling from the corner of the mouth after submandibular (submandibular gland) gland excision?

Drooling from the Corner of the Mouth After Submandibular Gland Excision

Drooling from the corner of the mouth after submandibular gland excision is most likely due to injury of the marginal mandibular nerve (option d). This complication affects facial nerve function controlling the lower lip, leading to poor oral competence and subsequent saliva leakage.

Anatomical Considerations and Mechanism

• The marginal mandibular branch of the facial nerve innervates the muscles that control the lower lip, including the depressor anguli oris and depressor labii inferioris 1
• Injury to this nerve during submandibular gland surgery leads to weakness of the lower lip, resulting in decreased oral competence and subsequent drooling from the corner of the mouth 2
• The marginal mandibular nerve runs superficially in the neck, making it particularly vulnerable during the traditional transcervical approach to submandibular gland excision 3, 4

Differential Diagnosis of Post-Surgical Drooling

Marginal Mandibular Nerve Injury (Correct Answer)

• Results in weakness or paralysis of the lower lip on the affected side 2
• Causes inability to maintain oral seal, leading to drooling specifically from the corner of the mouth 3
• This nerve is at high risk during submandibular gland surgery due to its anatomical course 4

Why Other Options Are Incorrect:

• Lingual nerve injury (option a):

  • The lingual nerve provides sensory innervation to the anterior two-thirds of the tongue and floor of mouth 5
  • Injury causes numbness and taste disturbance, not drooling 5
  • While at risk during submandibular surgery, lingual nerve damage would not cause corner-of-mouth drooling 3

• Ansa cervicalis injury (option b):

  • The ansa cervicalis innervates the infrahyoid muscles (strap muscles) 1
  • Injury would affect neck movement and swallowing but not cause drooling 1
  • This nerve is deeper and less commonly injured during standard submandibular approaches 3

• Hypoglossal nerve injury (option c):

  • The hypoglossal nerve innervates the intrinsic and extrinsic muscles of the tongue 5
  • Injury causes tongue weakness, deviation toward the affected side, and potential speech/swallowing difficulties 5
  • While this can affect overall oral function, it does not specifically cause corner-of-mouth drooling 3

Clinical Implications and Management

• Drooling from marginal mandibular nerve injury may be temporary or permanent depending on the nature of nerve damage 2
• Management includes:
  • Physical therapy and facial exercises to improve muscle tone 2
  • Botulinum toxin injections to the contralateral side to improve symmetry in cases of permanent injury 6
  • Surgical options including nerve grafting or dynamic muscle transfers for severe cases with no recovery 2

Prevention Strategies

• Use of transoral approaches for submandibular gland removal can reduce risk to the marginal mandibular nerve 3, 4
• Careful identification and protection of the nerve during dissection is essential 3
• Robotic-assisted techniques may offer improved visualization and preservation of neural structures 4

Understanding the relationship between the marginal mandibular nerve and drooling from the corner of the mouth after submandibular gland excision is crucial for proper diagnosis and management of this surgical complication.