A radiological investigation of enzootic pneumonia in the pig

Twenty normal piglets were radiographed and necropsied. Bronchography was performed in seven of the animals. In dorso-ventral radiographs the borders of the heart are clearly outlined by the adjacent lung lobes. In lateral films the lung fields may be divided into a cranial portion extending from the thoracic inlet to the third pair of ribs and a triangular shaped caudal portion with its base the caudal border of the heart and its apex the phrenico-vertebral angle. Nine field cases of enzootic pneumonia and nine experimentally induced cases were examined radiologically. They were then necropsied and the radiological and pathological findings related to each other. Pulmonary consolidation was identified radiologically as areas of unaerated lung which caused loss of the borders of the heart and diaphragm (silhouette sign) and enhancement of the image of the segmental and smaller bronchi (air bronchogram sign). The silhouette sign correctly predicted pulmonary consolidation of lobes in 77 per cent of field cases and in 54 per cent of lobes of experimental cases. The air bronchogram sign correctly predicted consolidation in 73 per cent of lobes of field cases and 76 per cent of lobes of experimental cases. A radiological examination has limitations for determining whether pigs are free of enzootic pneumonia because foci of consolidation less than 2 cm3 may not be detected.