Prep for USMLEPrep for USMLE
         Forum      |     Resources New Posts   |   Register   |   Login





 Home cooked question II  



Post Reply  
  • 0/5
  • 1
  • 2
  • 3
  • 4
  • 5


Author5 Posts
  #1

Dr. Careless is in the OR doing a thyroidectomy. He has just ligated inferior thyroid artery in order to minimize the bleeding due to the resection, however, soon afterwards, his patient developed dyspnea. Which nerve is damaged?

A. N. laryngeus superior, ramus externa
B. N. laryngeus superior, ramus interna
C. N. laryngeus recurrens
D. Ansa cervicalis
E. Truncus sympathicus

Elaborate the mechanics if possible





  #2

Answer: (hopefully) Recurrent laryngeal because it is closest to inferior thyroid and innervates all the muscles of the larynx except the cricothyroid. Ligation of the superior thyroid artery would lead to damage to external superior branch innervation to cricothyroid.
Mechanism: The dyspnea might be due to damage of post. cricoarytnoid maybe which permits abduction of vocal cords, if these are damaged then air cant get through into trachea.


  #3

Very good.

Also, cricothyroid muscles will be the only one that's working, and their function is to increase the tension of the vocal ligament, meaning rima glotticum is closed even further = not even forced ventilation is possible.


  #4

above the vocal cord, the larynx is suplied by superior thyroid artery and superior larngeal nerve branch of vagus.

Below the vocal cord, the larynx is suplied by inferior thyroid artery and recurent laryngeal, branch of vagus.

so any lesion to the inferior thyroid artery, may cause lesion to the recurrent laryngeal nerve. So the answer is C.

correct me if any thing wrong.


  #5

The thing about home cooked question is that it’s not water proof. The question didn’t emphasize on a 2 important concepts needed to address dyspnea.

1.inferior thyroid artery has direct relation to vagus but not so much with recurent laryngeal, however, lesion of the vagus nerve at this position effectively equals to the damage to the recurent laryngeal, causing paralysis of the ipsilateral intrinsic muscles of the larynx except 1, as mentioned above. recurent laryngeal nerve has relation to oesophagus and trachea, lying the in the groove between the two.

2. In order to develop dyspnea, the surgeon has to damage both vagus nerves, causing closure of the rima glottidis. If only 1 vagus nerve is damaged, hoarseness is developed.






Bookmark and Share



This thread is closed, so you cannot post a reply.



Login or Register to post messages








show Similar forum topics

Home cooked question :D
Type II and Type II hypersensitivity
question II
show Related resources

Kaplan USMLE Step 1 Home Study Program
Conrad Fischer's Internal Medicine Question Book
Premier Review Home Study Kit








Advertise | Support | Premium | Contact