Lymphoid tissue enlarges when it gets infected. This is true of adenoids. The symptoms caused by enlarged adenoids are mostly due to where this lymphoid tissue is located. Remember, adenoids are at the very back of the nose. That's the spot where the Eustachian tubes open from either ear.
Eustachian tubes ventilate the ear.
So big adenoids can block airpassage in both the nose and the ears. This blockage of normal air ventilation can lead to both sinusitis and otitis media. The back of the nose is right above the throat, so it's a straight shot from the adenoids down to the top of the throat - where the vocal cords live. Nasal secretions can't clear easily and there seem to be frequent and very prolonged colds. Obstruction of the Eustachian tubes can cause both ear infections or defective hearing from middle ear fluid .