Tympanic membrane retraction

Tympanic membrane retraction describes a condition in which a part of the eardrum lies deeper within the ear than its normal position.

The eardrum comprises two parts, the pars tensa, which is the main part of the eardrum, and the pars flaccida, which is a smaller part of the eardrum located above the pars tensa. Either or both of these parts may become retracted. The retracted segment of eardrum is often known as a retraction pocket. The terms “atelectasis” or sometimes “adhesive otitis media” can be used to describe retraction of a large area of the pars tensa.

Tympanic membrane retraction is fairly common and has been observed in one quarter of a population of British school children. Retraction of both eardrums is less common than having a retraction in just one ear. It is more common in children with cleft palate. Tympanic membrane retraction also occurs in adults.

Attempts have been made to categorise the extent of tympanic membrane retraction though the validity of these classifications is limited.

Three factors must occur for the tympanic membrane to become retracted:

When gas pressure within the middle ear is less than atmospheric pressure, the eardrum can become sucked into the middle ear space. This is caused by inadequate opening of the Eustachian tube and absorption of air from the middle ear space. People with a patulous Eustachian tube may also cause negative middle ear pressure by repeatedly sniffing to try to keep their Eustachian tube closed.

The middle layer of the pars tensa is strengthened by fibres of collagen protein. This layer may be weaker in the postero-superior quadrant (top rear quarter) or after the eardrum heals after perforation or tympanostomy tubes (grommets) so predispose to retraction in these areas. The pars flaccida is prone to retraction as it does not contain the same stiffening layer of collagen.

All over the body, new skin cells are continually produced to replace old skin cells which dry out and slough off. Growth of new cells on the surface of the eardrum is unusual in that the new cells migrate over the surface and move out along the ear canal. Even if migration along the ear canal is blocked, new cells continue to grow so the surface of the eardrum becomes larger. This process of proliferation and migration can result in enlargement of a retraction pocket so that the eardrum expands and grows deeper into the ear.

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Wikipedia