Page 117 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

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(b)

(a)

(d)
(a) Lateral radiograph and (b) post-mortem image of a dog
8.10 ith traditional tracheal collapse characteri ed by flattened
tracheal rings and weakened, stretched dorsal trachealis muscle.
(c) Lateral radiograph and (d) post-mortem image of a dog with a
tracheal ‘malformation’, characterized by W-shaped tracheal cartilage
rings, located most commonly at the thoracic inlet. In (c), note the
radiographic pathognomonic sign of a dorsally located tracheal lumen
(arrowed) due to the deviated rings.

(c)

lumen of a flattened trachea (Hobson, 1976). Interestingly, Clinical signs
Yamamoto et al. (1998) identified a relatively low density Middle-aged toy breed dogs are most frequently affected
of nerve ganglia and nerve cell bodies in the normal and present with a history of intermittent, progressively
canine trachea near the thoracic inlet, when compared
worsening cough and/or respiratory difficulty. Clinical signs
with densities found in the same trachea at the level of
range from a mild ‘honking’ cough to severe life-threatening
the carina. An underlying structural abnormality of the
dyspnoea, cyanosis and collapse.
tracheal ring hyaline cartilage has also been reported.
Dallman et al. (1985, 1988) documented that the cartilage
of collapsed tracheas contained fewer chondrocytes and Diagnosis
reduced glycoprotein, calcium and chondroitin sulphate,
History and signalment, combined with an inducible cough
and appeared less homogeneous than normal tracheal
during manual compression of the trachea, are sufficient
cartilage. The hyaline cartilage matrix in some collapsed
criteria for a provisional diagnosis.
tracheal rings was completely replaced by fibrocartilage
(Dallman, 1981). Hamaide et al. (1998) confirmed a weak
but significant correlation between proteoglycan content Physical examination
and bio mechanical properties of normal canine tracheal It is important for the clinician to remain mindful of the pre-
ring cartilage. It remains unclear, however, whether these carious respiratory status of such animals. Simple observa-
structural abnormalities are the result of a degenerative tion can often reveal the location of an airway obstruction:
process occurring in normal hyaline cartilage, a failure of
the normal development of tracheal hyaline cartilage, or • Inspiratory stertor suggests an extrathoracic airway
the result of an underlying inflammatory process. More obstruction, as the subatmospheric pressure
recently, one of the authors [CW] has encountered a generated during inspiration collapses the cervical
tracheal ‘malformation’ which does not fall into either of trachea whilst the intrathoracic trachea expands with
the above classifications. In addition, over 50% of the other structures within the thorax
cases treated at the author’s practice fall within • Expiratory stertor suggests an intrathoracic
the ‘malformation’ classification in that there is a static, obstruction, as increased pressures generated within
fixed luminal obstruction of the trachea located at the the thorax during expiration collapse the airways and
level of the thoracic inlet (see Figure 8.10cd). vessels, and exhaled air expands the cervical trachea.

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