Adenoid hypertrophy reduces the flow of air through the nose during pronunciation, causing resonance disorder, children will have difficulty pronouncing the nasal sounds / m /, / n /, / ŋ /, in Vietnamese are / m /, / n /, / ng /, / nh/. Hypertrophic adenoids may cause hyponasality by obliterating the nasopharynx or obstructing the choanae.