Page 618 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.1 Introduction 593

VetBooks.ir positional abnormalities (e.g. epiglottic • Bronchial: increased visibility of the bronchial
entrapment) or sometimes difficult-to-visualise
tree due to chronic airway disease and
abnormalities (e.g. subepiglottic cysts).
mineralisation of the airway wall.
Remember that endoscopically-induced dorsal • Interstitial: increased density of the lung
displacement of the soft palate is common interstitium due to inflammation or fibrosis.
and does not necessarily indicate that this This is a common, but non-specific, equine
abnormality occurs during exercise. pulmonary radiographic abnormality.
• Trachea: the proximal trachea is relatively • Alveolar: air-filled bronchi (tubular lucencies)
insensitive and can be examined with little silhouetted against fluid-filled alveoli (radiopaque
coughing. Discharge from the lungs pools at the lung field) producing ‘air bronchograms’;
thoracic inlet. associated with pulmonary oedema.
• Carina and bronchial tree: the trachea becomes • Vascular: increased visibility of the pulmonary
progressively more sensitive along its length vasculature, seen in congenital conditions,
and beyond the carina the airway should be producing left-to-right shunts (e.g. ventricular
desensitised with 1% lidocaine. septal defect).

Upper respiratory tract and These changes indicate pathological changes and
thoracic radiography not specific diseases.
Some regions of the URT are not accessible for
endoscopy and radiography can provide valuable Thoracic ultrasonography
diagnostic information about dental disease, sinus This is very useful for identifying pleural fluid
disease, the dorsal nasal cavity and the bone and or peripheral pulmonary disease (where there is
cartilage skeleton (skull, maxillary and ethmoid decreased air in the peripheral lung, where lung
turbinates, nasal septum, sinus walls). All views of lesions extend into the pleural space or where there
the head and cranial neck regions of the URT can are adhesions between parietal and visceral pleura).
be obtained with standard general practice X-ray Normal lung is air filled and reflects the ultrasound
machines. There is considerable superimposition of beam, creating a bright white line at the air inter-
different structures in the head; therefore, lateral, face of the pulmonary surface and not revealing
dorsoventral and lateral oblique views are required lung detail. Changes in the visceral pleural sur-
to help interpretation. Computed tomography (CT) face create visible reverberation artefacts known
imaging of the head has greater diagnostic sensitiv- as ‘comet tails’. Pleural fluid is readily visible and
ity and specificity than radiography and, although ultrasound can provide valuable information about
requiring referral, may be more cost effective than the nature of the fluid (cellularity and fibrin con-
repeated radiographic examinations. tent) as well as its location within the pleural space
Thoracic radiography requires high-powered and whether there is pocketing. Ultrasound pro-
equipment and is not possible with small por- vides a valuable guide for both thoracocentesis and
table practice machines. Four overlapping lateral lung biopsy.
projections are required to image the lung field.
Indications for thoracic radiography are chronic Paranasal sinus percutaneous
unresponsive equine asthma (pulmonary fibro- centesis and sinuscopy
sis), exercise-induced pulmonary haemorrhage The boundaries of the maxillary sinus can generally
(EIPH) (focal consolidation), pleuropneumonia/ be defined as follows:
bronchopneumonia (pulmonary abscess, pul-
monary consolidation), mediastinal masses and • Dorsally: a line drawn from the medial canthus
thoracic trauma (pneumothorax). Interpreting of the eye to the nasoincisive notch.
thoracic radiographs requires recognition of the • Rostrally: the rostral limit of the facial crest.
four major pulmonary patterns: • Ventrally: the facial crest.