Page 271 - Clinical Manual of Small Animal Endosurgery

Otoendoscopy 259

quite well in the aqueous medium of otoendoscopy. Powers of 8–15 W
are usually adequate for most lesions in the ear. A detailed description
of lasers, laser physics and laser endosurgery can be found in other texts.
Suffice to say that these diode lasers are a great aid in performing myrin-
gotomies, ablation of proliferative inflammatory lesions, control of
haemorrhage, and resection of polyps and other masses.

Anatomy

The canine and feline outer ear is defined by the external pinna to the
vertical canal (Fig. 9.5). The origination of the vertical canal is edged
ventrally and laterally by the intertragic notch, a separation between two
cartilaginous ridges: cranial and caudal. This can serve as an important
landmark for initial insertion of the endoscope. The length and angle of
the vertical ear canal varies from breed to breed and between canine to
feline. The epithelium of the vertical canal is squamous in nature with
variable numbers of hair follicles and progressively more sebaceous and
ceruminous glands as the vertical canal progresses deep. The angle
forming the demarcation between the vertical and horizontal canals is
defined by a firm ridge of cartilage extending caudo-ventrally. Navigating
this angle is often times the most challenging portion of otoendoscopy
for the novice. The severity of this angle is less in cats and brachycephalic
dog breeds, resulting in a more accessible horizontal canal.
The tympanum (Fig. 9.6) is a thin, glistening membrane forming the
separation from the external ear and middle ear, at the terminus of the
horizontal canal. In the normal ear, the pars flaccida of the tympanum
is seen dorsally, occupying approximately one-third of the field of view
of the structure. The pars tensa occupies the ventral two-thirds of the
visible tympanum and is clinically the more important portion of it (Fig.
9.7). In the normal patient, a bony ridge separating the tympanic cavity
from the bulla can be seen ventrally through the pars tensa, while dorso-
caudally the manubrium of the malleus in the middle ear is visible (Fig.
9.8). The opacity of the membrane sometimes limits visualisation of these
landmarks, although this more often occurs in the diseased intact tym-
panum (Fig. 9.9). In conditions where the tympanum is ruptured, either
via pathology or iatrogenically/therapeutically, with careful cleaning and
irrigation, these structures are easily visualised.

Patient preparation

Generally, most patients presenting to have a detailed otoendoscopic
exam and/or endoscopic surgery have had a long list of empirical thera-
pies attempted prior to the exam. As such, a careful anamnesis and
evaluation of previous clinical pathology studies is indicated. Following
the general physical exam a careful neurological exam is also advised.