Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 75
B
A
Fig. 2-48 A 5-year-old female mixed breed dog with a 4-month history of chronic cough that had
not responded to antibiotics and bronchial dilators. The thoracic cavity is markedly widened at its
caudal aspect in both the lateral (A) and the ventrodorsal (B) radiographs. The sternum diverges at
an acute angle from the thoracic spine. This thoracic conformation is referred to as pigeon chest.
Diagnosis: Normal thorax.
between the diaphragm and liver. Discriminating between diaphragmatic, pleural, or mediastinal
masses, diaphragmatic hernias with herniation of a liver lobe, and caudal or accessory
lung lobe masses can be challenging. The manner in which the mass moves, whether
with the lung or the diaphragm, may be a useful feature in determining the origin of a mass
in the region of the diaphragm.
H E R N I A S
Diaphragmatic Hernia. Diaphragmatic hernias allow protrusion of abdominal viscera
through the diaphragm. The protrusions alter the shape of the diaphragm. Several different
kinds of acquired and congenital diaphragmatic hernias may occur. 77,80-88 These
include traumatic or congenital diaphragmatic hernia, hiatal hernia, and pericardial
diaphragmatic hernia. Although congenital diaphragmatic hernias occur, most diaphragmatic
hernias are the result of trauma. Many congenital diaphragmatic hernias are associated
with sternal anomalies. 89 Occasionally there may be other medical considerations due
to the organs involved and their positions in the hernia. 90,91 In most cases, the diagnosis of
traumatic diaphragmatic hernia can be easily confirmed radiographically. When large
amounts of pleural fluid are present and only a portion of the liver is herniated, the diagnosis
may be difficult. The presence of gas-, food-, or fluid-filled portions of the gastrointestinal
tract within the pleural space is the most reliable radiographic evidence of
diaphragmatic hernia (Fig. 2-49). The bowel should be recognized because of its typical
size, shape, and density. Obstruction of the bowel may occur and result in bowel distention,
which could turn a chronic diaphragmatic hernia into an acute condition. Loss of the
diaphragmatic outline is a sign of diaphragmatic hernia. However, this may occur with any
type of pleural fluid and with pulmonary, pleural, or caudal mediastinal masses that arise
from or contact the diaphragm. Horizontal-beam techniques can be used to displace the
pleural fluid away from the segment of the diaphragm suspected to be affected, by making