How does anatomy affect placement of ventilation tubes in the treatment of acute otitis media (AOM)?

Updated: Sep 25, 2019
  • Author: John D Donaldson, MD, FRCSC, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Incision of the tympanic membrane is primarily governed by the relations of the structures behind the membrane (see the images below). The tympanic membrane can be divided into quadrants with an imaginary line drawn vertically along the long process of the malleus and extending to the inferior annulus, along with a horizontal line at the umbo. Generally, it can safely be incised in all quadrants except the posterior superior section, behind which lie the incus and stapes, structures that might be injured inadvertently by incision in this area. The area above the pars tensa, the pars flaccida, should be avoided.

Healthy tympanic membrane. Healthy tympanic membrane.
Drawing of normal right tympanic membrane. Note ou Drawing of normal right tympanic membrane. Note outward curvature of pars tensa (*) of eardrum. Tympanic annulus is indicated anteriorly (a), inferiorly (i), and posteriorly (P). M = long process of malleus; I = incus; L = lateral (short) process of malleus.

Two other structures, the facial nerve and the round window, are generally protected from any but the clumsiest of surgeons, the former by its high position in the middle ear and the latter by the overhanging niche.

Tubes are generally placed anteriorly, either superiorly or inferiorly. Because the posterior segments are deeper and have more vibratory motion, posterior placement gives a greater dampening effect. Anteriorly, any incision should avoid exposure of the malleus, the malleolar ligament, and the annulus; such exposure creates a greater tendency for perforations to persist after extrusion of the tube.


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