Tympanostomy tubes: an overview.

What do tympanostomy tubes do? If you look at all the names we have for them, you see that they have traditionally performed many functions:

* We call them vent tubes because they ventilate the middle ear. We know that a collapsed atelectatic middle ear can be saved by inserting a ventilation tube, if we do it early enough.

* We call them pressure-equalizing tubes because they allow atmospheric pressure changes to be balanced across the tympanic membrane when the eustachian tube is blocked.

* We call them drainage tubes because they allow fluid to drain from the middle ear in cases when a nonfunctioning eustachian tube is unlikely to regain its function anytime soon.

* We call them artificial eustachian tubes because in a sense they bypass a nonfunctioning eustachian tube and allow for ventilation of the middle ear cavity, equalization of atmospheric pressure changes, and the drainage of any fluids produced in the middle ear cleft.

Tubes as medication portals

Recently, we have begun to take advantage of a new use for these tubes. We are using the lumen of tubes as a gateway or portal through which we can instill topical medications (e.g., antibiotic eardrops) into the middle ear. Delivering drops in this manner requires some help from our patients, who will have to learn to perform tragal pumping in order to push the drops through the tube and into the middle ear cleft. Tragal pumping can produce a pressure of 20 cm [H.sub.2]O.

Types of tubes

Length. Short tubes have two flanges; one is placed inside the drum and the other outside. The inside flange prevents the tube from extruding too quickly, and the outside flange prevents the tube from falling back into the inner ear. Long tubes have only a single flange, which is placed inside the drum and which prevents the tube from falling out prematurely. Fluid moves in and out of a short tube more easily than it does in a long tube. Therefore, short tubes are better than long tubes for delivering medication into the middle ear. A long tube is not suitable for this purpose because its lumen is elevated above the surface of the tympanic membrane.

Lumen. The diameter of narrow-bore tubes ranges from 0.8 to 1.0 mm; wide-bore tubes have a diameter of 1.2 to 1.4 mm. Narrow-bore tubes are associated with a lower incidence of perforation, but they can become plugged more easily. Medication and other fluids pass more easily through wide-bore tubes. Narrow-bore tubes are better for swimmers.

Some tubes have an open lumen, and some have a semipermeable membrane. However, I don't believe that we will be seeing much more of the latter, because if a patient develops otitis media with a semipermeable tube in place, it's as if he or she has no tube at all because the fluid cannot drain.

Material. Tubes are made of both metal and synthetic materials. I prefer stainless-steel grommets because they can be cleaned, resterilized, and reused. Also, metal tubes have a better ratio of inner to outer diameter. Tubes have been manufactured with gold plating, with different coatings to alter surface tension and provide wetness, and even with delayed-release antibiotics. But we don't have a lot of evidence as to whether these additions have any worthwhile effect on things such as fluid drainage, prevention of plugging or further infection, or the formation of tube granuloma. But as Dr. Deitmer points out, some studies have shown that certain coatings are beneficial (page 7).

Tube granuloma

Tube granuloma is a specific entity (figure 1.) Patients with tube granuloma exhibit bloody otorrhea, and parents often call the office very worried because "my child's ear is bleeding." Other than the drainage, no pain or other symptom s occur. Examination of the ear will reveal that the granulation tissue is cherry red. Granulation tissue is not epithelialized, so it weeps and is very friable. If you were to remove the tube, which is usually not necessary, you would see that this represents a foreign-body granuloma related to keratin squames.

[FIGURE 1 OMITTED]

Treatment of tube granuloma is fairly simple, and it begins with reassurance. In most cases, a combination antibiotic/steroid eardrop for 1 or 2 weeks is sufficient to dissolve the granulation tissue. Refractory cases are rare, but when they do occur, the tube can be removed. In fact, in most stubborn cases, these tubes are no longer in the tympanic membrane; instead, they are resting on its surface.

We might be able to lower the risk of tube granuloma by being careful not to implant keratin squames intraoperatively. A study is underway in Canadato determine whether the application of topical ciprofloxacin/ dexamethasone during tube placement might prevent tube granuloma.

Plugging

Tubes may become blocked by blood and by inspissated debris (figure 2). Blockage is caused by sustained drainage from the middle ear. You can see how this occurs by putting some mucoid fluid on a slide and letting it dry. When the water evaporates, you are left with a golden-yellow crust. Again, Dr. Deitmer has some study data on tube blockage (page 7).

[FIGURE 2 OMITTED]

Extrusion

Extrusion is related to the phenomenon of epithelial migration and to the presence of the keratin squames that develop around the shaft (figure 3). I also believe that extrusion is associated with the type of flange. A tube with a single inner flange is less likely to extrude than is a double-flange tube. With the latter, keratin can develop under the outer flange and lift the tube out.

[FIGURE 3 OMITTED]