Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 79
Congenital diaphragmatic hernias are seen infrequently. It is difficult to distinguish
them clinically from traumatic hernias, because the radiographic signs are the same.
Congenital defects are most often on the ventral midline and the xiphoid frequently is
involved. Malformation of the sternum, including absence or splitting of the xiphoid or
alteration in the shape and number of the sternebrae, may be identified.
Sonographic changes associated with diaphragmatic hernias usually are restricted to
the identification of hydrothorax or abdominal structures or both in abnormal locations
(Fig. 2-54). 26 The most commonly involved organ is the liver. It is important to identify
carefully a structure as liver because atelectatic lung, lung lobe torsion, and pulmonary or
pleural neoplasms can mimic closely the sonographic appearance of liver.
It is usually very difficult to identify specifically a diaphragmatic rent, because the
diaphragm itself is rarely seen sonographically. The hyperechoic line that normally is seen
between the liver and lung is really the interface between the diaphragm (tissue) and lung
(air). If there is a diaphragmatic defect, the interface between liver and lung will also appear
as a thin, hyperechoic line.
Esophageal Hiatal Hernia. Although hernias potentially may occur around the caval or
aortic hiatus, only those around the esophageal hiatus have been reported. 94-103 Esophageal
hiatal hernias have been subdivided into three types: axial hiatal hernia, paraesophageal
hernia, and combined hernia. An oval or semicircular soft-tissue density may be visible
protruding from the diaphragm in the lateral radiograph at the level of the esophageal hiatus.
The soft-tissue density will extend on the ventrodorsal view into the caudal mediastinum
on or slightly to the left of the midline. Secondary esophageal dilation with food,
fluid, or gas may be identified. Gas within the stomach will outline the rugal fold pattern
and allow recognition of the stomach’s position cranial to the diaphragm. In some
instances, the rugal folds may be traced caudally through the diaphragmatic opening into
the abdominal portion of the stomach (Fig. 2-55). Many hiatal hernias are termed sliding
(i.e., the stomach may move into and out of the caudal mediastinum on sequential radiographs).
An esophageal contrast study is necessary in most instances to distinguish
between axial hiatal hernia, in which the stomach protrudes through the esophageal hiatus,
and paraesophageal hernia, in which the stomach protrudes through a diaphragmatic
opening lateral to the hiatus. Sonographically, the stomach may be seen protruding cranially
beyond the rest of the abdominal viscera with a hiatal hernia.
Fig. 2-52 A 2-year-old male Cairn
Terrier with mild exercise intolerance.
The dog had run away a week
prior to being found and brought for
treatment. Examination of survey
radiographs revealed an increased
density in the caudal and ventral
portion of the thorax. A positive
contrast celiogram reveals extravasation
of the contrast media across the
diaphragm and into the thoracic
cavity (arrow). Diagnosis:
Diaphragmatic hernia.