Pars Tensa and Pars Flaccida

A 25-year-old medical student is on her pediatric medicine rotation. She has questions about ear anatomy after examining her 11 AM patient. She obtained this image using the Wispr otoscope and would like to understand the significance of the pars tensa and the pars flaccida portions of the tympanic membrane.

Which of the following is true?

A. Acute otitis media (AOM) and Valsalva changes first present in the pars flaccida.
B. AOM and Valsalva changes first present in the pars tensa.
C. AOM first presents in the pars flaccida and Valsalva changes in the pars tensa.
D. AOM first presents in the pars tensa and Valsalva changes in the pars flaccida.

There are two distinct areas to the tympanic membrane (eardrum), the pars flaccida and the pars tensa. These two areas are outlined in the following images.

The pars tensa is the portion of the tympanic membrane that is the largest. It's what people tend to think of when they think of the “eardrum.” As the name suggests, it is “taut,” much like if you stretched plastic wrap on top of a bowl. You could also imagine the pars tensa to be similar to a drum surface. It is the portion of the eardrum responsible for translating sound waves into mechanical movement. Because it is “taut,” it is less likely to respond to changes in middle ear pressure from infection (AOM) or Valsalva. Valsalva is the maneuver you perform to clear your ears when in a descending airplane. It’s performed by holding your nose closed and increasing the pressure in your mouth. Via the Eustachian tube, this increase in mouth pressure is communicated to the middle ear space and “clears” your ears.

The pars flaccida, as the name suggests, drapes loosely across the posterior-superior portion of the eardrum. Because it is not as taut as the pars tensa, it responds earlier to changes in the middle ear space pressure. The pars flaccida will be the first place that bulging of the tympanic membrane is seen due to increased pressure in the middle ear space.  The pars flaccida is where most eardrum movement would be appreciated if mobility of the eardrum was evaluated via either pneumatic otoscopy or a Valsalva maneuver.

Key learning points

1. The pars flaccida is in the posterior-superior portion of the tympanic membrane.
2. The pars flaccida is where the first signs of increased middle ear pressure are seen.
3. The pars tensa occupies the majority of the tympanic membrane and is the surface most involved in sound translation.