The tube connecting the ear and the nose is called the Eustachian tube. The function of the tube is to allow passage of air into the ear, so that there is equalisation of pressure in the ear and the atmosphere. When there is any blockage of the tube, it causes fluid to collect in the ear this is called Serous Otitis Media.
In case of your son, his adenoids have got enlarged and this is blocking the tubes. This is the reason he is having ear problems. Though you might not percieve any problems directly, his doctors would have realised that he has serous otitis media and this is why they have advised the sdenoidectomy.
You should go through the operation in order that he does not develop any chronic ear problems.
You can look up here:
http://www.med.umn.edu/otol/library/serousot.htm
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