Page 278 - Clinical Manual of Small Animal Endosurgery

266 Clinical Manual of Small Animal Endosurgery

representative middle-ear sample for cytological and bacteriological eval-
uation but it certainly can be attempted. A sterile guarded culturette or
sterile polypropylene catheter are the preferred tools for this task. If the
tympanum is intact, but middle-ear disease is suspected based on the gross
appearance of the tympanum (and adjunctive imaging studies), a myrin-
gotomy can be performed. The myringotomy has been much maligned in
veterinary practice but when used appropriately and judiciously its role
in the management of otitis media cannot be underestimated.
A myringotomy can be performed with a variety of instrumentation.
Specially designed myringotomy knives are available but are designed
for the human patient where navigating the vertical canal towards
the horizontal ear canal is not an issue. These can be used in some feline
patients. A flexible, small-diameter endoscopic needle can be used via
the otoendoscope but frequently the diameter of these needles (25-gauge)
limits the effectiveness of the myringotomy. Biopsy or grasping forceps
can also be used to make a few punctate holes in the tympanum. Often,
if there is increased pressure in the middle ear behind the tympanum, a
single puncture will allow a larger tear to result. This author uses the
diode laser to perform the myringotomy. In this case, a smaller-diameter
fibre, usually 600 µm, is used. With a power setting of 6–10 W, a cruciate-
type linear incision is made in the pars tensa of the tympanum, beginning
in the craniodorsal aspect and extending caudo-ventrally. The next inci-
sion is made caudo-dorsal to cranio-ventral. The advantages of using
the laser with this pattern of myringotomy cut involve delayed surgical
healing of the tympanum. With good postoperative medical management
the canine and feline tympanum can heal very quickly; indeed, in many
cases more quickly than one would prefer. In an effort to provide a longer
period of middle-ear drainage, the laser myringotomy may prove
superior to other methodologies. One of the results of the thermal injury
from the laser is the region of cell death that occurs along the margins
of the incision. This cell death will produce the effect of delayed healing.
While in many clinical scenarios this would be counterproductive,
here it achieves the benefit of the desired longer period of middle-ear
drainage.
In virtually any event, the tympanic membrane will heal quite ade-
quately with reasonable medical management. With the myringotomy
performed and samples obtained for clinical pathology, gentle irrigation
of the middle ear will help remove any fluid or more inspissated material
from the middle ear.

Selected pathologies of the ear canals and middle ear

While a complete treatise on the pathologies of the ear in dogs and cats
is beyond the scope of this chapter, the practitioner must learn to appre-
ciate the most commonly encountered disease conditions seen via an
otoendoscopic exam.