Adenoids are a mass of lymphoid tissue located in the upper part of the throat, behind the nasal cavities. They are also known as the pharyngeal tonsils.
Adenoids play an important role in the body's immune system, trapping bacteria and viruses that enter through the nose and mouth and helping to fight infection.
When they become infected, they can swell up and cause problems with breathing and sleeping.
This can cause difficulty breathing, especially when lying down. Adenoidectomy is a surgical procedure to remove adenoids.