Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 77
Fig. 2-50 A 7-year-old mixed breed
dog had been hit by a car and had a
mild degree of respiratory distress. A
dorsally recumbent, horizontalbeam
lateral view of the thorax
reveals a liver lobe protruding
through the diaphragmatic cupola
(arrow). Note the pleural fluid,
which had previously obscured the
herniated liver lobe, has been shifted
into the paraspinal region by the
effects of gravity due to the positioning.
Diagnosis: Diaphragmatic
hernia.
the suspected area higher than any other segment (Fig. 2-50). Diaphragmatic hernias usually
result in displacement of the thoracic viscera (Fig. 2-51). The degree and direction of
the displacement will vary with the hernia site and amount of abdominal viscera within the
pleural space. On occasion, only the stomach will herniate into the pleural space and
become distended with gas. This will appear as a homogeneous gas density that has no
pulmonary vessels and that displaces the cardiac silhouette and pulmonary parenchyma. It
is critical that gastric involvement in diaphragmatic hernias be recognized, because these
can become acute, life-threatening emergencies if the stomach dilates and significantly
interferes with respiration. 85
In addition to the thoracic radiographic changes, the abdominal radiograph also will be
useful. The stomach may be positioned closer to the diaphragmatic outline when the liver
herniates into the thorax. In many obese cats and in many dogs, the falciform ligament contains
enough fat to outline the ventral abdominal margin of the diaphragm. Loss of this
shadow in an obese animal with pleural fluid, but without peritoneal fluid, often indicates a
diagnosis of diaphragmatic hernia. In some animals with diaphragmatic hernia, the absence
of normal viscera from the abdomen will permit the diagnosis of diaphragmatic hernia. Rib
fractures, especially those involving the caudal ribs, may be detected also. Diaphragmatic
tears may occur without herniation and may not be detectable radiographically.
Barium contrast examinations of the stomach and small intestine may be helpful when
the diagnosis is not obvious on the survey film. Positioning of the stomach close to the
diaphragm or identification of bowel within the thorax confirms the diagnosis of
diaphragmatic hernia.
Positive and negative contrast peritoneography have been used to evaluate the
diaphragm. 92,93 Injection of 1 to 2 ml/kg of body weight of water-soluble positive-contrast
medium into the peritoneal cavity, followed by right and left lateral, sternal, and dorsal
recumbent radiographs, allows complete evaluation of the diaphragm. Identification
of contrast within the pleural space confirms the diagnosis of diaphragmatic rupture (Fig.
2-52). Air, carbon dioxide, or nitrous oxide also may be used. The gas is injected into
the peritoneal cavity, and its identification in the pleural cavity confirms the diagnosis (Fig.
2-53). Positional maneuvers, including horizontal-beam radiography, can be used to move
the gas or positive-contrast medium between the liver and the diaphragm, thereby outlining
the abdominal surface of the diaphragm. In chronic diaphragmatic hernias, adhesions
of the viscera to the diaphragm can interfere with contrast flow into the pleural space and
cause a false-negative study.