The adenoid, also known as a pharyngeal tonsil or nasopharyngeal tonsil is a collection of aggregated lymphoid nodules that occur on the posterior wall and roof of the nasopharynx, where the nose blends into the throat. Normally, in children, it forms a soft mound in the roof and posterior wall of the nasopharynx, just above and behind the uvula. The adenoid, unlike other types of tonsils, has pseudostratified columnar ciliated epithelium. It also differs from the other tonsil types by lacking crypts. The adenoid is often removed along with the tonsils. An enlarged adenoid, or adenoid hypertrophy, can become nearly the size of a ping pong ball and completely block airflow through the nasal passages. Even if the enlarged adenoid is not substantial enough to physically block the back of the nose, it can obstruct airflow enough so that breathing through the nose requires an uncomfortable amount of work, and inhalation occurs instead through an open mouth. The enlarged adenoid can also obstruct the nasal airway enough to affect the voice without actually stopping nasal airflow altogether. Enlargement of the adenoid, especially in children, causes an atypical appearance of the face, often referred to as adenoid face. Features of adenoid faces include mouth breathing, an elongated face, prominent incisors, hypoplastic maxilla, short upper lip, elevated nostrils, and a high arched palate. Surgical removal of the adenoid is a procedure called adenoidectomy. Adenoid infection may cause symptoms such as excessive mucus production, which can be treated by its removal. Studies have shown that adenoid regrowth occurs in as many as 20% of the cases after removal. Carried out through the mouth under a general anaesthetic (or less commonly a topical), adenoidectomy involves the adenoid being curetted, cauterised, lasered, or otherwise ablated.