Page 671 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

646 CHAPTER 3

VetBooks.ir 3.87

LEFT RIGHT
Fig. 3.87 Ultrasonography of a horse with left-sided 4-BAD. The horse presented for surgery for recurrent
laryngeal neuropathy, but palpation confirmed agenesis of the left wing of the thyroid cartilage. The cricoid
cartilage (red arrows) are normal, but the left thyroid cartilage (yellow arrows) is shorter and does not overlap
the cricoid, compared with the normal right side.

3.88 Fig. 3.88 Dynamic overground endoscopy of a
horse with right-sided rostral displacement of the
palatopharyngeal arch.

Endoscopic examination can reveal asymmetry of
the arytenoid cartilages, typical of RLN, or it can be
normal. Rostral displacement of the palatopharyn-
geal arch is clearly visible endoscopically as a rim of
tissue partly obscuring or overlying the dorsal aspect
of the arytenoid cartilages (Fig. 3.88). RDPPA can
be unilateral or bilateral.
Radiography of the larynx and proximal tra-
chea may reveal air in the proximal oesophagus.
This finding is usually only present if RDPPA is
visible endoscopically. Occasional horses show no
abnormalities at rest and treadmill endoscopy is
necessary to reveal dynamic rostral displacement
findings is absence of the wing of the thyroid carti- of the palatopharyngeal arch or dynamic vocal fold
lage. In this case the complete ring of the cricoid can collapse.
be palpated, feeling similar to a large tracheal ring.
In front of the cricoid is a space, palpably similar to Management
the cricotracheal space, but comparison with the There is no effective treatment for rostral displace-
contralateral side should prevent any confusion over ment of the palatopharyngeal arch and the abnor-
the precise location of the structures. mality is permanent. Many horses with laryngeal
Ultrasonographic examination can confirm hypo- dysplasia maintain arytenoid abduction at exercise
plasia of the wing of the thyroid cartilage (Fig. 3.87). but have bilateral collapse of the vocal cords, and
CT studies and MRI have also been used to confirm bilateral ventriculectomy and cordectomy can be an
abnormalities of the cartilage skeleton. effective treatment in such cases. Arytenoidectomy