What is the function of the levator labii superioris alaeque nasi muscle and how do neuromodulators like Botox (Botulinum toxin) affect it?

Function of Levator Labii Superioris Alaeque Nasi and Effects of Botulinum Toxin

The levator labii superioris alaeque nasi (LLSAN) muscle elevates the upper lip and nasal ala during facial expressions, and botulinum toxin injections effectively paralyze this muscle by blocking acetylcholine release at the neuromuscular junction, resulting in softening of the nasolabial fold and improvement in nasal tip drooping.

Anatomy and Function of LLSAN

The LLSAN is a facial muscle with important cosmetic and functional roles:

• Location and Attachments:

  • Originates from the frontal process of the maxilla
  • Inserts into the medial nasolabial fold and alar base 1
  • The broadest portion is typically located approximately 8.4 mm inferior and 4.6 mm medial to the medial canthus 1

• Primary Functions:

  • Elevates the upper lip
  • Elevates and dilates the nasal ala (nostril)
  • Contributes to the formation of the nasolabial fold
  • Acts as a transitional muscle that conjugates with other nasal and perinasal muscles 2

• Anatomical Variations:

  • Can present in different shapes: rectangular (83%), fan (10%), or trapezoid (7%) 3
  • Medial fibers attach to the deep surface of the alar facial crease and intermingle with the alar part of the nasalis 3
  • Some deeper muscle fibers extend to the vestibular skin of the nasal lobule 3

Mechanism of Botulinum Toxin on LLSAN

Botulinum toxin (BTX) works through a specific mechanism:

1. Pharmacological Action:

   • BTX enters the vascular circulation (through injection in cosmetic applications)
   • Transported to peripheral cholinergic nerve terminals at neuromuscular junctions
   • Blocks acetylcholine transmission across the neuromuscular junction by inhibiting acetylcholine release from the presynaptic motor neuron terminal 4
   • Results in temporary flaccid paralysis of the injected muscle

2. Molecular Mechanism:

   • Heavy-chain binding to neuronal cell
   • Internalization via receptor-mediated endocytosis
   • Translocation to the cytosol
   • Cleavage of proteins involved in acetylcholine release 4

Cosmetic Effects of Botulinum Toxin on LLSAN

Injection of botulinum toxin into the LLSAN produces several aesthetic benefits:

• Nasolabial Region Improvements:

  • Softening of the nasolabial fold, particularly the medial portion 2, 5
  • Improvement in the drooping of the nasal tip 2
  • Shortening of the lip philtrum when smiling 2

• Global Facial Effects when combined with injections to other facial muscles:

  • Eyebrow tail lifting
  • Softening of crow's feet
  • Overall improvement in facial expressions 2

Injection Technique

For optimal results when injecting the LLSAN:

• Target Location:

  • The broadest portion of the superior LLSAN (approximately 8.4 mm inferior and 4.6 mm medial to the medial canthus) 1
  • Consider the anatomical variations in shape and attachments

• Guidance Methods:

  • EMG guidance may be useful for precise localization, particularly in complex cases 4
  • However, anatomical landmarks can also be used effectively for most cosmetic applications

• Considerations:

  • Understanding the local nasal muscular dynamics is crucial as LLSAN interacts with other facial muscles 2
  • The elevated portion of the upper lip muscle may become stronger as the nasal part of the LLSAN is paralyzed 2

Potential Complications

When using botulinum toxin on the LLSAN, be aware of:

• Common Side Effects:

  • Temporary weakness of adjacent muscles
  • Asymmetry in facial expressions
  • Changes in smile dynamics

• Rare Complications:

  • Ptosis
  • Vertical deviations
  • Injection site reactions

Clinical Applications Beyond Cosmetics

The LLSAN has additional clinical relevance:

• Surgical Applications:

  • The LLSAN can be used as a pedicled flap for reconstruction of full-thickness nasal defects 6
  • Resection of the LLSAN muscle can improve the acute nasolabial angle and medial nasolabial fold in facial rejuvenation procedures 5

• Medical Applications:

  • Botulinum toxin injection may be useful in cases of hyperkinetic nasal muscles causing functional issues

Understanding the anatomy and function of the LLSAN is essential for achieving optimal results with botulinum toxin injections while minimizing complications.