The adenoid is sometimes referred to as nasopharyngeal tonsils. Like the tonsils proper, they are a body of lymphoid tissue whose main function is to act as a filter to trap potentially harmful organisms. They are located at the base of the nose (in the back of the throat) quite close to the tonsils. Until they cause problems, most people are completely oblivious to their existence.
When the adenoids are active (i.e. fighting infections and producing antibodies) they can become quite enlarged. While this enlargement is necessary, it is not without its side-effects, one of the most common among young children being the blocking of the eustachian tube (which connects the middle ear to the throat) resulting in the clogging of the natural drainage system for the middle ear.
Normally, the adenoids will not enlarge to such an extent that they will totally block the middle ear, but nevertheless any clogging of the middle ear can lead to recurring ear infections and can cause long-term damage to hearing if left unchecked.
If, following consultation, an ENT surgeon decides to perform an adenoidecotomy on a child under four years of age, he will probably not remove the tonsils unless they are causing problems as well. The tonsils will still have a useful role to play in trapping potentially harmful organisms.
However, since the adenoids and tonsils are so closely related and perform more or less the same function, they are very often removed together in the case of an older child who is going for either a tonsillectomy or an adenoidectomy.
When both tonsils and adenoids are removed together the surgical procedure used is referred to as a T&A.