142.What is antro-choanal polyp?  

polyps are composed of edematous,hyperplastic submucosal connective tissue and are relatively hypocellular. thats why they are of low density in CT scan and homogenous bright signal intensity on T2 weighted image.Variable densities of inflammatory cells are also found in this, and tend to be more concentrated towards the mucosal surface.This is said to be the cause of periphral rim enhancement.

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sure,thanks👍