Describe the Eustachian tube with its functions and disorders.

Anatomy and Function

• The eustachian (pharyngotympanic) tube connects the anterior wall of the middle ear to the lateral wall of the nasopharynx.
• It is about 36 mm long in the adult, and is cartilaginous in its medial two-thirds and bony in its lateral third, the narrowest point being the isthmus at their junction.
• It has three functions, and all three matter clinically: ventilation, equalising middle ear pressure with the atmosphere; drainage of middle ear secretions by mucociliary action toward the nasopharynx; and protection of the middle ear from nasopharyngeal sound, pressure and reflux

Disorders

• Obstruction (dysfunction) is much the commoner disorder, and follows from upper respiratory infection, allergic rhinitis, adenoid hypertrophy, cleft palate, sinusitis, barotrauma and nasopharyngeal carcinoma
• The sequence it produces is the basis of middle ear disease: obstruction → absorption of air and negative middle ear pressure → retraction of the drum → transudation of fluid (otitis media with effusion) → infection, adhesive otitis media, retraction pockets and cholesteatoma
• Symptoms — blocked ear, fullness, mild conductive hearing loss, popping or crackling, autophony and discomfort on flying or diving
• The single most important rule: a unilateral middle ear effusion in an adult is nasopharyngeal carcinoma until the postnasal space has been examined. This is particularly important in Northeast India and in populations of Chinese origin, and the effusion is often the first and only symptom
• In cleft palate the tensor veli palatini is abnormally inserted.
• Barotrauma — on descent in an aircraft or while diving, ambient pressure rises and the tube tends to lock, so pressure cannot be equalised. This causes pain, retraction, haemorrhage into the drum and effusion. Prevention is by swallowing, yawning and Valsalva during descent, avoiding flying with an upper respiratory infection, and decongestants
• Patulous Eustachian tube is the opposite disorder — the tube remains abnormally open, causing autophony, hearing one’s own breathing, and a sensation of blockage. It follows marked weight loss, pregnancy and radiotherapy, and is characteristically relieved by lying down or by a head-down position.
• Treatment — treat the nose and the underlying cause; autoinflation; adenoidectomy where the adenoid is obstructing; grommet insertion for persistent effusion; and balloon Eustachian tuboplasty in selected adults
• The infant tube is shorter, wider and horizontal, which is the whole explanation of paediatric otitis media
• Do not feed an infant lying flat; reflux into the middle ear through a horizontal tube is a direct consequence of the anatomy