Overview

Length (adult)≈36 mm (3.5–4 cm)

Bony : cartilaginous1/3 : 2/3

Angle to horizontal≈45° adult; ≈10° infant

The auditory (pharyngotympanic, Eustachian) tube runs anteriorly, medially and inferiorly from the anterior wall of the tympanic cavity to the lateral wall of the nasopharynx, opening behind the inferior nasal concha. In adults it makes an angle of ≈45° with the horizontal. Its lateral one-third (≈12 mm) is bony (in the petrous temporal bone, below the canal for tensor tympani); its medial two-thirds (≈24 mm) are cartilaginous (a hook-shaped cartilage completed by fibrous membrane). The narrowest point, the isthmus, is at the junction. The pharyngeal end of the cartilage raises the torus tubarius, behind which lies the pharyngeal recess (fossa of Rosenmüller) — the commonest site of nasopharyngeal carcinoma.

The cartilaginous part is normally closed, protecting the middle ear from nasopharyngeal secretions and the sound of one's own voice. It opens briefly during swallowing and yawning, mainly through the action of tensor veli palatini (V3), assisted by levator veli palatini and salpingopharyngeus (pharyngeal plexus, X). It is lined by ciliated pseudostratified columnar epithelium with goblet cells, which clears mucus towards the pharynx.

In infants the tube is shorter (≈18 mm), wider and nearly horizontal (≈10°), with a less efficient tensor veli palatini — so nasopharyngeal infection reaches the middle ear easily and drainage is poor: the anatomical basis of the high incidence of otitis media in children.

Location: From the anterior wall of the tympanic cavity to the lateral wall of the nasopharynx (level of the inferior nasal meatus).

Parts & subdivisions

Bony part (lateral 1/3)
In the petrous temporal bone; always open.
Cartilaginous part (medial 2/3)
Normally closed; opened by tensor veli palatini.
Isthmus
Narrowest point (≈1–2 mm) at the bony–cartilaginous junction.
Pharyngeal opening and torus tubarius
Surrounded by tubal tonsil (part of Waldeyer ring) and the salpingopharyngeal fold.

Anatomy

Innervation: Tympanic plexus (IX) — bony part; pharyngeal branch of the pterygopalatine ganglion (V2) — cartilaginous part. Muscles: tensor veli palatini (V3), levator veli palatini and salpingopharyngeus (vagus via pharyngeal plexus).
Arterial supply: Ascending pharyngeal artery, middle meningeal artery and artery of the pterygoid canal.
Histology: Ciliated pseudostratified columnar epithelium with goblet cells; lymphoid tissue (tubal tonsil) near the pharyngeal opening.
Development: First pharyngeal pouch (tubotympanic recess).

Function

Equalise middle-ear pressure with atmospheric pressure
Drain middle-ear secretions to the nasopharynx (mucociliary clearance)
Protect the middle ear from nasopharyngeal reflux and sound

Clinical significance

Otitis media in children

Short, wide, horizontal tubes plus enlarged adenoids obstructing the tubal openings predispose to acute otitis media and glue ear. Cleft palate (dysfunctional tensor veli palatini) almost always causes otitis media with effusion.

Eustachian tube dysfunction and barotrauma

If the tube cannot open (upper respiratory infection, allergy) during descent in an aircraft or diving, negative middle-ear pressure retracts the drum, causing pain, effusion or haemotympanum. Valsalva manoeuvre or swallowing helps. A patulous (abnormally open) tube causes autophony (hearing one's own voice loudly), e.g. after weight loss.

Nasopharyngeal carcinoma

Arising in the fossa of Rosenmüller, it may present in an adult as unilateral otitis media with effusion — which must prompt nasopharyngoscopy.

Test yourself

Why are children more prone to acute otitis media than adults?

Their auditory tube is shorter, wider and more horizontal
Their tympanic membrane lacks a fibrous layer
Their external acoustic meatus is entirely bony
Their middle ear lacks a mucosal lining

Answer: Their auditory tube is shorter, wider and more horizontal

The infant auditory tube is ≈18 mm long and nearly horizontal (≈10° vs ≈45° in adults) with a less efficient tensor veli palatini, so nasopharyngeal pathogens reach the middle ear easily and drainage is poor; enlarged adenoids add obstruction.