Vocal Cord Paralysis: Causes, Nerve Palsy - NEET PG ENT

Vocal cord paralysis is a medical condition in which the ability to control the muscles that control the movement of vocal cords is lost. In vocal cord paralysis, there are two nerves; they are the superior laryngeal nerve and the recurrent laryngeal nerve.

Read this blog further to get a quick overview of this important topic for ENT  and ace your NEET PG exam preparation.

Anatomy of Neck Region

Mandible, hyoid bone, clavicle, mediastinum, thyroid cartilage (midline of the neck), cricoid cartilage (continuous Inferior early as the trachea), cervical trachea (part of the trachea that lies in the neck), thoracic trachea.

Membranes In The Neck

• CricoThyroid membrane - Between the cricoid cartilage and thyroid cartilage
• Thyrohoid membrane - It is present Between thyroid cartilage and hyoid bone
• Cricotracheal membrane - It is present Between Cricoid and trachea

Nerves In The Neck

• Vagus Nerve - It is Superior, at the level of the hyoid bone. It is found on the left and right side of the neck.
• Superior Laryngeal Nerve - It is a branch of the vagus. It divides into two branches, one entering the larynx.
• Internal Laryngeal Nerve - One of the branches of the superior laryngeal nerve. Pierced into the thyrohyoid membrane and supplies sensory nerves to the larynx and muscles except for the Cricothyroid muscle.
• External Laryngeal Nerve - Other branches of the superior laryngeal nerve supply only cricothyroid muscle.

Vagus nerve goes into the neck and cross  near subclavian artery and then enter  into the trachea and oesophageal groove. The right Vagus nerve gives off a branch recurrent laryngeal nerve at the level of the subclavian artery and winds around the subclavian artery. Superior laryngeal nerve supplies to above the larynx. The recurrent laryngeal nerve supplies below the larynx. Recurrent laryngeal nerve does not supply to the muscle of the pharynx. Superior laryngeal nerve is at the same position on both sides. The left vagus gives recurrent laryngeal nerve at the level of the arch of Iota. Recurrent laryngeal nerve supplies to the lower of the vocal cord and larynx except the cricothyroid. Left Recurrent laryngeal nerve goes into the mediastinum. Sensory Anastomosis is formed between the internal laryngeal nerve and the recurrent laryngeal nerve, which is Galen's  anastomosis.

Innervations of Superior Laryngeal Nerve

Sensory part of the superior laryngeal nerve is called the Internal laryngeal nerve, and the motor part is called the external laryngeal nerve. The sensory part innervates mucosa of the larynx, which is above vocal cords and the motor innervates cricothyroid muscle.

Innervations of Recurrent Laryngeal Nerve         

Recurrent laryngeal nerve  supplies all laryngeal muscles except cricothyroid

Function of the Muscles          

Causes of Vocal Cord Paralysis            

• Direct trauma: It can be surgical trauma from thyroid surgery ( most common)
• Idiopathy: Malignancies in the thyroid and larynx in the neck. Malignancies in the lung can cause vocal cord paralysis. 
• Orton syndrome (cardiovascular syndrome): is when there is a left atrial hypertrophy which causes compression on the left recurrent laryngeal nerve.
• Turner syndrome and other nerve palsies.
• Infections: viral neuritis, so the left side is most affected here.

Phonation 

During phonation vocal cords adduct and become tense. In paralysis of cricothyroid, vocal cords remain flaccid, sloopy and fail to adduct completely. So voice is affected in cricothyroid paralysis.

Cricothyroid Paralysis           

When the cricothyroid is paralysed, voice will be affected. During phonation, the vocal cord comes to the midline, and the cricothyroid is used. During respiration, the posterior cricothyroid help in abducting the vocal cords. If it is recurrent laryngeal nerve palsy, the posterior cricothyroid will be paralysed.

How Respiration and Phonation are Affected by Nerve Paralysis?            

When breathing, the vocal cord goes away from the midline and is done by the posterior cricothyroid muscle. If there is recurrent laryngeal nerve palsy, respiration will also be affected. cricothyroid  is pulling the vocal cord back to the midline, so if there is superior laryngeal nerve palsy, respiration will be affected too.

Movement of Vocal Cord      

SLN pulls the vocal cord towards the midline. RLN pulls away from the midline. The vocal cord will be in an immediate position 3.5mm away from midline (cadaveric position). During breathing, tensors tense and pull the vocal cord away from the middle (7mm or 9mm distance). The air passes, but for respiration, the vocal cord comes back to midline.

If there is right recurrent laryngeal nerve palsy, only one side is paralyzed  The right side recurrent laryngeal nerve palsy will lead to a sensory loss of the lower half of larynx and motor loss for all the muscles except cricothyroid. Position- the paralyzed cord will come in midline. As the right side post cricothyroid is paralysed which is abductor of vocal cords.Phonation will be slightly affected. Also, respiration is not be affected much because there is a space for air to pass through, but there will be dyspnoea during exertion.

Nerve palsy

Unilateral Recurrent Laryngeal Nerve Palsy

In this the Position of the vocal cords is  paralysed cord is in midline. The Phonation- slightly affected,Respiration- not affected much but dyspnoea can be seen during exertion.in this condition the Treatment is to  wait and watch.          

Bilateral Recurrent Laryngeal Nerve  Paralysis               

All muscles will be paralyzed on both sides except the cricothyroid. Phonation is not affected much since the vocal cord line is completely in the midline.Respiration is affected. It can cause palsy stridor.Palsy stridor is a high pitch squeaking or whistling sound. The treatment for this is tracheostomy followed by lateralization of the vocal cords.

Unilateral Superior Laryngeal Nerve Palsy     

Sensory loss - will be there on the upper half of larynx on the same side.

Motor loss - only cricothyroid is paralyzed. rest all muscles are functional.

Phonation : paralyzed cord will go into the abducted position as the cricothyroid is paralyzed. The vocal cords will be in an Askew position. So, pitch and tone will be affected. Respiration will not be affected but there is risk of aspiration.Treatment is medialisation of vocal cord is achieved with type 1 thyroplasty.

Bilateral Superior Laryngeal Nerve Palsy

Sensory loss above half of the vocal cord will happen on both sides.Motor loss on paralyzed sides and only cricothyroid would be paralyzed on both sides , rest all muscles are functional.Position - The vocal becomes wavy loose, and lacks, and the vocal cords get pulled away from the midline completely. Phonation will be significantly affected. aphonia occurs. Respiration - The space will increase between the vocal cords and midline, so there is no phonation and a higher risk of aspiration (the action or process of drawing breath). The respiration will not be affected, but there is the risk of aspiration; Treatment is the medialization of vocal cords by thyroplasty, Epiglottopexy, tracheo esophageal diversion.

Unilateral Combined Palsy

If both RLN and  SLN are lost together, sensory loss will be there on the affected site,Phonation is affected but the patient can speak. Respiration will not be adversely affected but dyspnoea can occur during exertion.

Bilateral Combined Palsy

Complete sensory loss of the entire larynx. All muscles will be paralysed.Both paralyzed cords are floppy and lie in an intermediate position. Aphonia occurs  as cricothyroid muscle on both sides is paralyzed. Aphonia is seen in bilateral SLN palsy and bilateral combined palsy.Respiration not affected much. But the risk of moderate risk of aspiration as it is complete anesthesia of larynx. Cough reflux will be absent. Treatment includes Tracheostomy, Epiglottopexy, Vocal cord plication, Total laryngectomy.

ENT Preparation Articles:

Triangles of Vocal Cord Paralysis             

Beahr’s triangle

• Medial- Recurrent laryngeal nerve.
• Lateral- Lies common carotid artery.
• Superior- Inferior thyroid artery.

Lore’s Triangle

• Aim:  For identification of recurrent laryngeal nerve 
• Medial – Medial border is formed by trachea and esophagus 
• Lateral – Common carotid artery
• Superior – Surface of inferior pole of thyroid gland

Simon's Triangle

• Aim: used to identify the recurrent laryngeal nerve
• Boundaries : 
• Anterior border: Is formed by the recurrent laryngeal nerve
• Posteriorly: Lies the common carotid artery
• Base : Cricothyroid muscle

Joll’s Triangle

• Aim : It is  used to identify the external branch of superior laryngeal nerve
• Lateral border : The upper pole of thyroid gland and superior thyroid vessels 
• Superiorly: Attachment of strap muscles
• Floor is formed by cricothyroid muscle

Cricothyroid space of Reeves: This is supposed to be an avascular space between the upper pole of thyroid and the cricothyroid muscle. Dissection confined to this area helps the surgeon in avoiding injury to the surrounding important structures like the superior laryngeal nerve.

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