Page 626 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.2 Surgical conditions of the respir atory tr act 601

VetBooks.ir adhesion formation to the nasal conchae that can Diagnosis
Endoscopic examination is definitive (Fig. 3.13) but
limit the horse’s resulting airway.
CHOANAL ATRESIA/STENOSIS it can be difficult to interpret as the endoscope can-
not be passed through to the pharynx. Examination
via the contralateral nares usually allows orienta-
Definition/overview tion and subsequent diagnosis (in a unilateral case).
This is a rare congenital condition involving failure Contrast radiography has been used to delineate
of the development, or narrowing, of a hole (the cho- the deformity. In stenosis cases, one or both of the
ana) between the nasal passages and the nasophar- entrances from the nasal passages to the nasophar-
ynx. It can be unilateral or bilateral. Bilateral cases ynx may appear narrowed.
are almost invariably fatal at birth. Unilateral cases
will usually survive but have a poor athletic potential. Management
Occasionally, there is a congenital narrowing or ste- If bilateral, then life support would require orotra-
nosis of the airway at this level that presents later in cheal intubation or a tracheotomy. If the atresia
life as a respiratory noise and/or exercise intolerance. is membranous then endoscopic laser surgery to
ablate the membrane is possible. Many cases are
Aetiology/pathophysiology much more substantial, with thickened tissue and
The nostrils develop caudally by the fusion of the bone present, and a frontonasal bone flap has been
palatine processes. The bucconasal membrane sepa- used to allow surgical removal of the obstruction.
rating the nasal cavities from the pharyngeal cavity Intranasal surgery using laparoscopic instruments
thins progressively until it is two layers of epithelium
(oral and nasal). The membrane perforates before
parturition. The precise cause of failure of this
membrane to rupture is unknown. In man, choanal 3.13
atresia is frequently (47%) associated with other con-
genital abnormalities including ocular, cardiac and
genitourinary defects.

Clinical presentation
Bilateral cases present with severe respiratory dis-
tress at birth. Foals are almost invariably dead by the
time veterinary attention is available but occasional
cases learn to mouth breathe and survive.
Unilaterally affected horses usually present at a
young age, with respiratory signs. The presentation
varies, associated with any other abnormalities, but
includes respiratory noise, lack of airflow from one
nostril and reduced exercise tolerance.

Differential diagnosis
Bilateral: all causes of respiratory obstruction and Fig. 3.13 Endoscopic view of a unilateral (left
distress in the newborn foal – most importantly side) choanal atresia. The left side of the picture
aspiration of fetal fluids and membranes. Unilateral: is the caudal nasal septum, the upper aspect is the
other causes of respiratory distress in the young ethmoturbinates, the right side is the caudal ventral
horse, including permanent dorsal displacement turbinate and the lower aspect is the abnormal
of the soft palate and an expansile mass within the membrane covering the upper part of the ventral
paranasal sinuses, including sinus cysts. meatus.