Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 91
Fig. 2-64 A middle-aged dog with a history of dyspnea and
discomfort. A and B, Lateral and ventrodorsal radiographs
revealed pleural fluid especially in the right cranial thorax.
The cardiac silhouette is obscured. There are bronchial
structures present in the area of the right cranial lung lobe
anterior to the cardiac silhouette in A. The entire right lung
is obscured in B. However, in A a bronchus was noted traversing
caudal and dorsal to the heart. Following a bronchogram
(C), a suspected torsion of the right middle lobe
was confirmed. The occluded stump of the twisted right
middle lobar bronchus is indicated by an arrow. Diagnosis:
Lung lobe torsion. An exploratory thoracotomy was performed
and a right middle lung lobe torsion was identified.
A
B
C
The role that pleural fluid accumulation plays in the misdiagnosis of pulmonary disease
should not be minimized. A fibrinous pleural fluid that “traps” over a lung lobe may
give the appearance of pulmonary lobar disease. The presence of an internal pulmonary
structure within the density (e.g., air bronchogram signs, bronchial thickening) indicates
pulmonary disease. However, the absence of a pulmonary pattern suggests pleural disease
but does not exclude pulmonary involvement. Confirmation may require ultrasonography
or computed tomography.
Fat accumulates in the mediastinum, dorsal to the sternum, adjacent to the pericardium,
and beneath the parietal pleura in obese dogs and cats. This may be mistaken for pleural fluid.
This fat density does not obliterate completely the diaphragm or cardiac silhouette and, therefore,
it can be recognized as a fat density. Despite a large amount of density in the ventral thorax,
the pleural fissure lines will not be observed when fat rather than fluid accumulates in the
pleural space. Changes in the animal’s position will not change the position of this fat density.