Guide to the interpretation of lung patterns in small animals

Lung changes are routinely divided into alveolar; bronchial or interstitial lung patterns. The greatest increase in ung opacity occurs with an alveolar lung pattern. Obscuring of lung vessels and silhouetting of other soft tissue structures, like the heart or the diaphragm, are major findings in alveolar lung changes. The lung appears like a mirror image of a normal lung showing a light grey background with black branching lines. The number of differential diagnoses can often significantly be reduced if the distribution of alveolar changes are taken into account. In contrast, bronchial lung changes lead to a mild to moderate increase in lung opacity due to a thickening of the bronchial walls, which appear as tramlines or rings (donuts) on the radiograph. Bronchial mineralisations and bronchiectasia represent subgroups of bronchial lung patterns. The list of differential diagnoses is relatively short. A diffuse, unstructured interstitial lung pattern can lead to a mild as well as a severe increase in lung opacity. The lung appears as if a fly net has been superimposed onto it. The list of differential diagnoses is long. A nodular interstitial lung pattern is characterised by multiple soft tissue nodules of a diameter of more than 5 mm, while a miliary lung pattern is characterised by multiple nodules of less than 5 mm in diameter. The most common diagnosis associated with a nodular or miliary interstitial lung pattern is primary or secondary neoplasia, however other differential diagnoses are possible.