This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Operative Surgery, Subject name: ENT
Level of tracheostomy is by which of the following anatomical landmark? (Repeat) 
Select and explain. 
A. Cricoid cartilage, B. Isthumus of thyroid, C. 2nd tracheal ring, D. 3rd tracheal ring
B: Isthumus of thyroid
Answer: B: Isthumus of thyroid 
Explanation: Ans: B (Isthmus of the thyroid) Ref: Diseases of the Ear Nose and Throat by PL Dhingra 5th edn .2010.Page 337Explanation:Types of tracheostomy based on positionHigh tracheostomy - Above the thyroid isthmus through the first tracheal ringIncreased risk of sub glottic edema and stenosisMid tracheostomy - At the level of thyroid isthmus, through the 2nd or 3rd tracheal ringIsthmus is divided or retractedMost commonly doneLow tracheostomy - Below the isthmusIncreased risk of injury to great vessels in the neck