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Laryngeal Photos: Paralysis: Unilateral Paralysis | |
Initially after an injuryUnilateral paralysis shows up in different ways on examination depending on when the injury occurred and to what degree a nerve was injured. Initially the affected vocal cord will typically be ABducted, or away from the midline, and not moving (open and closed). The voice may range from normal if spoken softely, but is usually weak or poor or nonexistant if a loud voice is attempted. The voice will flutter sound like a loose sail in the wind. Choking on liquids is frequently a problem. Breathing will be fine, that is to say, no noise or restriction in breathing, though it is quite common to feel “out of breath”. The vocal cords actually typically close partway during expiration (breathing out) to provide some resistance and keep the lungs full of air. When the lungs do not stay full with air, the alveoli in the lungs collapse. Like a balloon that is completely deflated, it is hard to get the alveoli open again. A partially inflated balloon is much easier to fill (try blowing up an empty balloon vs. a partially inflated one). A lung that is partially filled with air is easier to add air to. The ability to close the vocal cords, keeps the lungs partially inflated when breathing out. As time goes by, if the nerve to the vocal cords is intact (not cut) the vocal cords will regain innervation or a nerve supply. The recovery is quite variable, but frequently the weakend vocal cord is progressively held closer and closer toward the midline. So, several months after an injury the voice will begin to improve and choking will be less of a problem. There are many variations in the appearance of the cords because of the variable degree to which each of the several weakened muscles of the voicebox may have recovered. Unilateral paralysis is often idiopathic (the cause is unknown - though I would suspect a virus as is the case in Bells palsy, a viral injury of the facial nerve). It is also caused by iatrogenic injury - meaning that it is caused inadvertently by a physician. Thyroid surgery, carotid artery surgery, anterior cervical fusion are some of the common surgical causes of the recurrent laryngeal nerves. Also after a tube has been in the windpipe for breathing during anesthesia or other reason, the inflated cuff of the ballon can injure the laryngeal nerve(s) where they enter the larynx. | |
Thyroarytenoid muscle injury | |
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If the flexible scope is placed into the laryngeal inlet, the relative size of the vocal cords can be assessed and this predicts the size of the underlying thyroarytenoid muscle within the vocal cord. The left cord is very thin here suggesting it has not had a nerve input for some time. |
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When the paralysis does not involve the entire recurrent laryngeal nerve, the weak side may still close or approximate at the level of the vocal process. In this case then, the lateral cricoarytenoid (LCA) muscle is working. However, on breathing out or during phonation, the weakend vocal cord buckles outward as on the left side here. The patient tends to compensate by raising the pitch of the vibration and this would stretch the vocal cord and eliminate this buckling to some degree (an obligate falsetto). |
Lateral cricoarytenoid muscle injury | |
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The vocal cord opens normally for breathing. |
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Closure is incomplete as the LCA muscle fails to move the vocal process to the midline. The vocal cords come partway together because the interarytenoid muscle is working. |
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The main key to identifing involvement of the lateral cricoarytenoid muscle, in a paralysis, is to lift the arytenoids out of the way with the flexible scope and the posterior glottic closure is visualized. Here, the left vocal process is canted laterally instead of straight. |
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On close up exam with the flexible laryngoscope, the mass of the vocal cord muscles is nearly identical. |
| See also the diagnosis section. | |
Photos by James P. Thomas, MD
Updated 21 April 2004 |