Page 664 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.2 Surgical conditions of the respir atory tr act 639

VetBooks.ir be felt as a sharp promontory on one side. Some is hypoechoic with intermittent hyperechoic flecks
scattered through the stroma. As neurogenic atro-
clinicians use the slap response in assessing these
cases.
ing in a more even and hyperechoic appearance
Ultrasonographic examination is also diagnostic phy progresses the muscle becomes fibrotic, result-
and may be more predictive of laryngeal function (Fig. 3.76).
at rest than endoscopy. Using a high-frequency Endoscopic examination of the arytenoid car-
probe the lateral aspect of the larynx is examined. tilage is initially undertaken at rest. The normal
The laryngeal cartilages are hypoechoic and the movements of the larynx should be observed care-
cricoarytenoideus lateralis is identified between fully for a few minutes. Bilaterally symmetrical
the thyroid and cricoid cartilages. Normal muscle abduction of the arytenoids occurs during inspira-
tion. Asymmetry of the rima glottides is obvious in
severe cases but can be subtle and more difficult to
3.75 assess in milder degrees of the disease. The larynx
should be examined with the endoscope passed up
both nostrils to negate the effect of the eccentric
positioning of the endoscope in the nasopharynx.
Some horses have a degree of asynchronous move-
ment of the arytenoids at rest and it can be difficult
to assess the significance of this. The effect of nasal
occlusion and deglutition (stimulated by flushing
water down the endoscope through the biopsy chan-
nel) in inducing abduction of the arytenoids should
also be observed.
The degree of laryngeal neuropathy can be
classified by one of many scoring systems. The
one recommended here is the Havermeyer system
(Table 3.1).
Dynamic endoscopy is used when complete assess-
ment of laryngeal function is required (Fig. 3.77).
It is particularly useful in clarifying the significance
Fig. 3.75 Palpation of the dorsal aspect of of asynchronous movement of the arytenoids, grades
the larynx, to ascertain the depth of the dorsal II.2–III.1 (Fig. 3.78). At high speeds collapse of the
cricoarytenoid muscle.

3.76

T T

C
C
Fig. 3.76 Ultrasonographic
image showing fibrosis of the
left cricoarytenoideus lateralis A
A
muscle (arrow). T, thyroid
cartilage; C, cricoid cartilage; Left Airway lumen Airway lumen Right
A, arytenoid cartilage.