Tympanic Membrane (Eardrum)
The tympanic membrane (TM) is a thin, translucent, cone-shaped membrane that separates the external auditory canal from the middle ear cavity. It is essential for transmitting sound vibrations to the ossicles.
Anatomical Zones
- Pars Tensa: The larger, taut, inferior portion consisting of three layers (outer epithelial, middle fibrous, inner mucosal).
- Pars Flaccida (Shrapnell’s Membrane): The smaller, superior, flaccid portion lacking the fibrous layer. It is a common site for retraction pockets and cholesteatoma formation.
Otoscopic Examination
| Landmark | Description |
|---|---|
| Cone of Light | Reflected light is located in the anteroinferior quadrant. |
| Umbo | The tip of the manubrium of the malleus is the most depressed part of the TM. |
| Malleus | The manubrium (handle) is visible, extending from the center to the periphery. |
High-Yield Exam Pearl:
- Myringotomy: A surgical incision made in the TM to drain middle ear fluid. It is typically performed in the posteroinferior quadrant to avoid injury to the ossicles and the chorda tympani nerve.
- Appearance: A normal TM is pearly gray, mobile, and intact. Redness (erythema) and bulging suggest acute otitis media.