Page 684 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.2 Surgical conditions of the respir atory tr act 659

VetBooks.ir TRACHEAL COLLAPSE Exercise-induced pulmonary haemorrhage may
occur in severe cases because of increased thoracic
Definition/overview
Tracheal collapse is an uncommon condition seen in pressures. Scabbard trachea of the Thoroughbred
may often be asymptomatic but may present as poor
a variety of situations. The most important form is performance with respiratory noise.
an idiopathic dorsoventral collapse, frequently intra-
thoracic, almost always in small ponies and donkeys, Differential diagnosis
especially Shetlands and miniature ponies. A lateral For dorsoventral tracheal collapse of the pony the
collapse (scabbard trachea) of the cervical trachea primary differential diagnosis is recurrent airway
is also reported in the Thoroughbred and crosses. obstruction, such as allergy to fungal spores com-
Typically, there is dyspnoea and stridor with diag- mon in hay or straw, or summer pasture-associated
nosis achieved by external tracheal palpation, endos- airway obstruction.
copy and lateral neck and thoracic radiographs. Both
conservative and surgical treatments have been suc- Diagnosis
cessfully used. Palpation of the trachea in the dorsoventral defor-
mity may reveal a sharpened edge to the lateral
Aetiology/pathophysiology aspects, especially in the cranial part of the neck.
Tracheal collapse can develop secondary to condi- Difficulties may be encountered in palpation dis-
tions such as: external compression from enlarged tally (where the defects are most common) and in
lymph nodes, abscesses and tumours (mediastinal), thick skinned, fat small ponies. In the scabbard tra-
trauma around the trachea or to the structure itself, chea deformity palpation will often reveal distinctive
temporarily due to severe expiratory dyspnoea as ridges on the ventral midline of the deformed tra-
a result of pulmonary disease and during standing chea in the upper cervical region. Diagnosis is usu-
sedation if animals rest their necks on bars at the ally achieved by endoscopy (Fig. 3.106). Markedly
front of stocks. Lateral tracheal flattening (scabbard
trachea) in the first few tracheal rings is common 3.106
in the Thoroughbred and crosses but is often inci-
dental. Dorsoventral tracheal collapse in ponies is
the most common form and is caused by a tracheal
cartilage ring deformity, although the precise aeti-
ology is not known. Some cases are seen in young
animals, which may be developmental, but many are
in older animals and could be degenerative in origin.
The condition is usually associated with flattening
of the tracheal cartilage rings (reducing dorsoventral
distance), with resultant stretching of the dorsal tra-
cheal ligament. Other sorts of deformity may occur
concurrently at different sites.

Clinical presentation
In many small ponies and donkeys the condition
may be asymptomatic because of limited workload or
mild changes. Affected ponies usually present with a
history of respiratory distress, including significant Fig. 3.106 Marked collapse of the dorsal tracheal
respiratory stertor and coughing. The pony or horse ligament in a pony, concurrent with coughing. The
may be normal at rest and only show clinical signs pony was managed with corticosteroids and was found
during exertion or during hot or humid weather. dead in the field a few months later.