Diseases of the respiratory tract are a common reason why dogs and cats seek veterinary medical care. This lecture will focus on intrathoracic respiratory diseases which may manifest with clinical signs of cough, wheeze, exercise intolerance, tachypnea, and/or respiratory distress. There are a wide variety of diseases which affect the airways and pulmonary parenchymal which include infectious disorders (bacterial, fungal, viral, protozoal, parasitic), inflammatory processes (e.g., chronic bronchitis, asthma, eosinophilic bronchitis, aspiration pneumonia, foreign body pneumonia, eosinophilic pneumonia, etc.), neoplasia (primary or metastatic), pulmonary edema (noncardiogenic or cardiogenic), pulmonary hemorrhage, interstitial lung diseases, structural or functional disorders (hypoplastic trachea, collapsing trachea or mainstem bronchi, bronchomalacia, bronchiectasis, bronchopulmonary dysplasia, lung lobe torsion, bullae or cavitary lesions). Obtaining a thorough history and completing both a distance and hands on physical examination can provide important clues to help narrow the list of differentials, but ultimately other diagnostic tests need to be performed.
Traditionally, thoracic radiography has been critical to help discriminate cardiac versus pulmonary disease as a cause of the clinical signs. Thoracic radiography has widespread availability, is cost effective and provides rapid information about cardiac and pulmonary vessel size as well as information about the airways and pulmonary parenchyma. Radiography can also help determine if disease is focal, multifocal or diffuse and can give a general idea of anatomic severity (i.e., how much of the pulmonary parenchyma appears to be involved and if the changes are mild, moderate, or severe). However, there are important limitations to thoracic radiography which makes computed tomography appealing. Computed tomography allows for three dimensional reconstruction of anatomic structures with very good discrimination of tissue types.This lecture will use a series of clinical cases of respiratory disease in dogs and cats to highlight optimal use of each imaging modality.